Grade Level

Detecting the Electric Field

Saturday February 9, 2019

You are actually fairly familiar with electric fields too, but you may not know it. Have you ever rubbed your feet against the floor and then shocked your brother or sister? Have you ever zipped down a plastic slide and noticed that your hair is sticking straight up when you get to the bottom? Both phenomena are caused by electric fields and they are everywhere!

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An electric field exists when at least one body is electrically charged. Atoms are filled with positively charged protons and negatively charged electrons. If an object has more electrons than protons, it will be negatively charged and if it has fewer electrons than protons, it will be positively charged. Electric fields, like magnetic fields, can attract and repel. If two bodies have the same kind of charge, that is either both are negative or both are positive, they will push themselves away from each other. If one body has a positive charge and the other has a negative charge, they will attract each other. Charged bodies can also attract bodies that are neither positive nor negative but are just neutral.

Electric fields are extremely common. If you comb your hair with a plastic comb, you cause that comb to have a small electric field. When you take off a fleece jacket or a polyester sweat shirt, you create an electric field that may be thousands of volts! Don’t worry, you can’t get hurt. There may be lots of voltage but there will be very little amperage. It’s the amperage that actually hurts you.

Here’s a simple experiment you can do that only needs four simple items:
– head of hair
– balloon
– yardstick or meterstick
– large spoon

Here’s what you do:

Download Student Worksheet & Exercises

Make sure you’ve tried out these Static Electricity experiments and learn how to light a bulb without plugging it into the wall!

Exercises

What happens if you rub the balloon on other things, like a wool sweater?
If you position other people with charged balloons around the table, can you keep the yardstick going?
Can we see electrons?
How do you get rid of extra electrons?
Does the shape of the balloon matter?
Does hair color matter?
Rub a balloon on your head, and then lift it up about 6”. Why is the hair attracted to the balloon?
Why does the hair continue to stand on end after the balloon is taken away?
What other things does the balloon stick to besides the wall?
Why do you think the yardstick moved?
What other things are attracted or repelled the same way by the balloon? (Hint: try a ping pong ball.)

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Pinhole Camera

Saturday February 9, 2019

This is the simplest form of camera – no film, no batteries, and no moving parts that can break. The biggest problem with this camera is that the inlet hole is so tiny that it lets in such a small amount of light and makes a faint image. If you make the hole larger, you get a brighter image, but it’s much less focused. The more light rays coming through, the more they spread out the image out more and create a fuzzier picture. You’ll need to play with the size of the hole to get the best image.

While you can go crazy and take actual photos with this camera by sticking on a piece of undeveloped black and white film (use a moderately fast ASA rating), I recommend using tracing paper and a set of eyeballs to view your images. Here’s what you need to do:

Materials:

box
tracing paper
razor or scissors
tape
tack

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Download Student Worksheet & Exercises

Here’s the quick set of instructions:

1. Use a cardboard box that is light-proof (no leaks of light anywhere).
2. Seal light leaks with tape if you have to. Cut off one side of the box (Note – there’s no need to do this if you’re using a shoebox).
3. Tape a piece of tracing paper over the cutout side, keeping it taut and smooth.
4. Make a pinhole in the box side opposite of the tracing paper.
5. Point the pinhole at a window and move toward or away from the window until you see its image in clear focus on the tracing paper.

OPTIONAL: You can hold up a magnifying glass in front of the pinhole to sharpen the image.

Exercises

How do the images appear when they’re projected onto the paper inside your camera?
Why do you think it’s important to make the box as light-proof as possible?
Is there a part of your body that works similarly to the pinhole?
Sketch a picture of something you saw through your pinhole camera.

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Eyeballoon

Saturday February 9, 2019

In this lab, we are going to make an eyeball model using a balloon. This experiment should give you a better idea of how your eyes work. The way your brain actually sees things is still a mystery, but using the balloon we can get a good working model of how light gets to your brain.

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Here’s what you need

- 1 biconvex plastic lens
- 1 round balloon, white, 9 inches
- 1 assistant
- 1 votive candle
- 1 black marker
- 1 book of matches
- 1 metric ruler
- Adult Supervision!

Download Student Worksheet & Exercises

Here’s what you do

Blow up the balloon until it is about the size of a grapefruit. If it’s difficult to inflate, stretch the material a few times or ask an adult to help you.
You will need an extra set of hands for this portion. Ask your partner to hold the neck of the balloon closed to keep the air in while you insert the lens into the opening. The lens will need to be inserted perpendicularly to the balloon’s neck. It will prevent any air from escaping once it’s in place. Like your eye, light will enter through the lens and travel toward the back of the balloon.
Hold the balloon so that the lens is pointing toward you. Take the lens between your thumb and index finger. Look into the lens into the balloon. You should have a clear view of the inside. Start to twist the balloon a little and notice that the neck gets smaller like your pupils do when exposed to light. Practice opening and closing the balloon’s “pupil.”
Have an adult help you put the candle on the table and light it. Turn out the lights.
Put the balloon about 20 to 30 centimeters away from the candle with the lens pointed toward it. The balloon should be between you and the candle. You should see a projection of the candle’s flame on the back of the balloon’s surface. Move the balloon back and forth in order to better focus the image on the back of the balloon and then proceed with data collection.
Describe the image you see on the back of the balloon. How is it different from the flame you see with your eyes? Draw a picture of how the flame looks.
The focal length is the distance from the flame to the image on the balloon. Measure this distance and record it.
What happens if you lightly push down on the top of the balloon? Does this affect the image? You are experimenting with the affect caused by near-sightedness.
To approximate a farsighted eye, gently push in the front and back of the balloon to make it taller. How does this change what you see?

What’s going on?

Okay, let’s discuss the part of the balloon that relate to parts of your eye. The white portion of the balloon represents your sclera, which you may have already guessed is also the white part of your eye. It is actually a coating made of protein that covers the various muscle in your eye and holds everything together.

Of course, the lens you inserted represents the actual lens in your eye. The muscles surrounding the lens are called ciliary muscles and they are represented by the rubber neck of your balloon. The ciliary muscles help to control the amount of light entering your eyes.

The retina is in the back of your eye, which is represented by the inside back of your balloon. The retina supports your rods and cones. They collect information about light and color and send it to your brain.

Exercises

How does your eye work like a camera?
How can you tell if a lens is double convex?
What is the difference between convex and concave?
Can you give an example of an everyday object that has both a convex and a concave side?
How can you change the balloon to make it like a near-sighted eye?
How can you change the balloon to make it like a far-sighted eye?

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Hydraulic Pneumatic Earth Mover

Saturday February 9, 2019

When people mention the word “hydraulics”, they could be talking about pumps, turbines, hydropower, erosion, or river channel flow. The term “hydraulics” means using fluid power, and deals with machinesand devices that use liquids to move, lift, drive, and shove things around.

Liquids behave in certain ways: they are incompressible, meaning that you can’t pack the liquid into a tighter space than it already is occupying.

If you've ever filled a tube partway with water and moved it around, you've probably noticed that the water level will remain the same on either side of the tube.

However, if you add pressure to one end of the tube (by blowing into the tube), the water level will rise on the opposite side. If you decrease the pressure (by blowing across the top of one side), the water level will drop on the other side.

In physics, this is defined through Pascal's law, which tells us how the pressure applied to one surface can be transmitted to the other surface. As liquids can't be squished, whatever happens on one surface affects what occurs on the other. Examples of this effect include siphons, water towers, and dams. Scuba divers know that as they dive 30 feet underwater, the pressure doubles. This effect is also show in hydraulics - and more importantly, in the project we're about to do!

But first, let's understand what's happening with liquids and pressure:

Here’s an example: If you fill a glass full to the brim with water, you reach a point where for every drop you add on top, one drop will fall out. You simply can’t squish any more water molecules into the glass without losing at least the same amount. Excavators, jacks, and the brake lines in your car use hydraulics to lift huge amounts of weight, and the liquid used to transfer the force is usually oil at 10,000 psi.

Air, however, is compressible. When car tires are inflated, the hose shoves more and more air inside the tire, increasing the pressure (amount of air molecules in the tire). The more air you stuff into the tire, the higher the pressure rises. When machines use air to lift, move, spin, or drill, it’s called “pneumatics”. Air tools use compressed air or pure gases for pneumatic power, usually pressurized to 80-100 psi.

Different systems require either hydraulics or pneumatics. The advantage to using hydraulics lies in the fact that liquids are not compressible. Hydraulic systems minimize the “springy-ness” in a system because the liquid doesn’t absorb the energy being transferred, and the working fluids can handle much heavier loads than compressible gases. However, oil is flammable, very messy, and requires electricity to power the machines, making pneumatics the best choice for smaller applications, including air tools (to absorb excessive forces without injuring the user).

We're going to build our own hydraulic-pneumatic machine. Here's what you need to do: [am4show have='p8;p9;p11;p38;p92;p14;p41;p75;p88;' guest_error='Guest error message' user_error='User error message' ] Materials:

plastic cup
20 tongue-depressor-size popsicle sticks
6 syringes (anything in the 3-10mL size range will work)
6 brass fasteners
5’ of flexible tubing (diameter sized to fit over the nose of your syringes)
four wheels (use film canister lids, yogurt container lids, milk jug lids, etc.)
4 rubber bands
two naked (unwrapped) straws
skewers that fit inside your straws
hot glue gun (with glue sticks)
sharp scissors or razor (get adult help)
drill with small drill bits (you’ll be drilling a hole large enough to fit the stem of a brass fastener)

Let’s play with these different ideas right now and really “feel” the difference between hydraulics and pneumatics. Connect two syringes with a piece of flexible tubing. Cut the tubing into three equal-sized pieces and use one to experiment with. Shove the plunger on one syringe to the “empty”, and leave the other in the “filled” position before connecting the tubing. What happens when you push or lift one of the plungers? Is it quick to respond, or is there “slop” in the system?

Now remove both plungers and, leaving the tubing attached, fill the system with water to the brim on both ends (this is a good bath-time activity!). Keep the open ends of the syringes at the same level as you fill them. What happens if you lower one of the syringes? What happens when you raise it back up? Is there now air in your system?

Fill your syringe-tube system up with water again, keeping the plungers at the same height as you work. Insert one of the plungers into one of the syringes and play with the levels of the syringes again, lifting one and lowering the other. Now what happens, or doesn’t happen?

Why does that work? Because both syringes are open to the atmosphere, they both have equal amounts of air pressure pushing down on the surface of the water. When you raise one syringe higher than the other, you have increased the elevation head of higher syringe, which works to equalize the water levels in the two syringes (thus shoving water out of the lower syringe). Elevation head is due to the fluid’s weight (gravitational force) acting on the fluid and is related to the potential energy of the raised syringe (which increased with elevation).

Now connect your plungers into a fully hydraulic system: Push the plunger all the way down to expel the water from one of the syringes (water should leak all over the place from the open syringe). Now add the second plunger to the open syringe and push the plunger down halfway. What happens? You have just made a hydraulic system!

Are you ready to build it into a three-axis machine? Then click the play button below:

Download Student Worksheet [/am4show]

Simple Pulley Experiments

Saturday February 9, 2019

Are you curious about pulleys? This set of experiments will give you a good taste of what pulleys are, how to thread them up, and how you can use them to lift heavy things.

We’ll also learn how to take data with our setup and set the stage for doing the ultra-cool Pulley Lift experiments.

Are you ready?
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For this experiment, you will need:

One pulley (from the hardware store… get small ones that spin as freely as possible. You’ll need three single pulleys or if you can find one get a double pulley to make our later experiment easier.)
About four feet of string
2 paper cups
many little masses (about 50 marbles, pennies, washers etc.)
Yardstick or measuring tape
A scale (optional)
2 paper clips
Nail or some sort of sharp pokey thing
Table

Download Student Worksheet & Exercises

“Advanced students: Download your Simple Pulley Experiments

1. Take a look at the video to see how to make your “mass carriers”. Use the nail to poke a hole in both sides of the cup. Be careful to poke the cup…not your finger! Thread about 4 inches of string or a pipe cleaner through both holes. Make sure the string is a little loose. Make two of these mass carriers. One is going to be your load (what you lift) and the other is going to be your effort (the force that does the lifting).

2. Dangle the pulley from the table (check out the picture).

3. Bend your two paper clips into hooks.

4. Take about three feet of string and tie your paper clip hooks to both ends.

5. Thread your string through the pulley and let the ends dangle.

6. Put 40 masses (coins or whatever you’re using) into one of the mass carriers. Attach it to one of the strings and put it on the floor. This is your load.

7. Attach the other mass carrier to the other end of the string (which should be dangling a foot or less from the pulley). This is your effort.

8. Drop masses into the effort cup. Continue dropping until the effort can lift the load.

9. Once your effort lifts the load, you can collect some data. First allow the effort to lift the load about one foot (30 cm) into the air. This is best done if you manually pull the effort until the load is one foot off the ground. Measure how far the effort has to move to lift the load one foot.

10. When you have that measurement, you can either count the number of masses in the load and the effort cup or if you have a scale, you can get the mass of the load and the effort.

11. Write your data into your pulley data table in your science journal.

Double Pulley Experiment

You need:

Same stuff you needed in Experiment 1, except that now you need two pulleys.

1. Attach the string to the hook that’s on the bottom of your top pulley.

2. Thread the string through the bottom pulley.

3. Thread the string up and through the top pulley.

4. Attach the string to the effort.

5. Attach the load to the bottom pulley.

6. Once you get it all together, do the same thing as before. Put 40 masses in the load and put masses in the effort until it can lift the load.

7. When you get the load to lift, collect the data. How far does the effort have to move now in order to lift the load one foot (30 cm)? How many masses (or how much mass, if you have a scale) did it take to lift the load?

8. Enter your data into your pulley table in your science journal.

Triple Pulley Experiment

You Need

Same stuff as before

If you have a double pulley or three pulleys you can give this a shot. If not, don’t worry about this experiment.

Do the same thing you did in experiments 1 and 2 but just use 3 pulleys. It’s pretty tricky to rig up 3 pulleys so look carefully at the pictures. The top pulley in the picture is a double pulley.

1. Attach the string to the bottom pulley. The bottom pulley is the single pulley.

2. Thread the string up and through one of the pulleys in the top pulley. The top pulley is the double pulley.

3. Take the string and thread it through the bottom pulley.

4. Now keep going around and thread it again through the other pulley in the top (double) pulley.

5. Almost there. Attach the load to the bottom pulley.

6. Last, attach the effort to the string.

7. Phew, that’s it. Now play with it!

Take a look at the table and compare your data. If you have decent pulleys, you should get some nice results. For one pulley, you should have found that the amount of mass it takes to lift the load is about the same as the amount of mass of the load. Also, the distance the load moves is about the same as the distance the effort moves.

All you’re really doing with one pulley, is changing the direction of the force. The effort force is down but the load moves up.

Now, however, take a look at two pulleys. The mass needed to lift the load is now about half the force of the load itself! The distance changed too. Now the distance you needed to move the effort, is about twice the distance that the load moves. When you do a little math, you notice that, as always, work in equals work out (it won’t be exactly but it should be pretty close if your pulleys have low friction).

What happened with three pulleys? You needed about 1/3 the mass and 3 times the distance right? With a long enough rope, and enough pulleys you can lift anything! Just like with the lever, the pulley, like all simple machines, does a force and distance switcheroo.

The more distance the string has to move through the pulleys, the less force is needed to lift the object. The work in, is equal to the work out (allowing for loss of work due to friction) but the force needed is much less.

Exercises Answer the questions below:

What is the load and effort of a pulley? Draw a pulley and label it.
What is the best way to say what a simple machine helps us do?
1. Do work without changing force applied
2. Change the direction or strength of a force
3. Lift heavy shipping containers
4. None of these
Name one other type simple machine and an example:

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The SeeSaw

Saturday February 9, 2019

We’re going to use everyday objects to build a simple machine and learn how to take data. Sadly, most college students have trouble with these simple steps, so we’re getting you a head start here. The most complex science experiments all have these same steps that we’re about to do… just on a grander (and more expensive) scale. We’re going to break each piece down so you can really wrap your head around each step. Are you ready to put your new ideas to the test?

This experiment is for Advanced Students.

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You need:

A wooden ruler or a paint stick for the lever
Many pennies, quarters, or washers (many little somethings of the same mass)
A spool, eraser, pencil (anything that can be your fulcrum)
A ruler (to be your um….ruler)
Paper cups
Optional: A scale that can measure small amounts of mass (a kitchen scale is good)

Download Student Worksheet & Exercises

1. Tape one paper cup to each end of lever. (This allows for an easy way to hold the pennies on the lever.)

2. Set your fulcrum on the table and put your lever (ruler or paint stick) on top of it. Try to get the ruler to balance on the fulcrum.

3. Put five pennies on one side of your lever.

4. Now, put pennies, one at a time on the other side of your lever, this is your effort. Keep adding pennies until you get your lever to come close to balancing. Try to keep your fulcrum in the same place on your lever. You may even want to tape it there.

5. Count the pennies on the effort side and count the pennies on the load side. If you have a scale, you can weigh them as well. With the fulcrum in the middle you should see that the pennies/mass on both sides of the lever are close to equal.

6. This part’s a little tricky. Measure how high the lever was moved. On the load side, measure how far the lever moved up and on the effort side measure how far the lever moved down. Be sure to do the measuring at the very ends of the lever.

7. Write your results in your science journal as shown in the video.

8. Remove the pennies and do it all over again, this time move the fulcrum one inch (two centimeters) closer to the load side.

9. Continue moving the fulcrum closer to the load until it gets too tough to do. You’ll probably be able to get it an inch or two (two to four centimeters) from the load.

10. If you didn’t use a scale feel free to stop here. Don’t worry about the “work in” and “work out” parts of the table. Take a look at your table and check out your results. Can you draw any conclusions about the distance the load moved, the distance the effort moved, and the amount of force required to move it?

11. If you used a scale to get the masses you can find out how much work you did. Remember that work=force x distance. The table will tell you how to find work for the effort side (work in) and for the load side (work out). You can multiply what you have or if you’d like to convert to Joules, which is a unit of work, feel free to convert your distance measurements to meters and your mass measurements to Newtons. Then you can multiply meters times Newtons and get Joules which is a unit of work.

1 inch = .025 meters

1 cm = .01 meter

1 ounce =0.278 Newtons

1 gram = 0.0098 Newtons

By taking a look at your data and by all the other work we did this lesson, you can see the beautiful switcheroo of simple machines. Simple machines sacrifice distance for force. With the lever, the farther you had to push the lever, the less force had to be used to move the load.

The work done by the effort is the same as the work done on the load. By doing a little force/distance switcheroo, moving the load requires much less force to do the work. In other words, it’s much easier. Anything that makes work easier gets a thumbs up by me! Hooray for simple machines!

Exercises

What is work?
1. Force against an object
2. Force over distance
3. 9 hours and sweat
4. Energy applied to an object
What is the unit we use to measure energy?
1. Newton
2. Watt
3. Joule
4. Horsepower
Describe a first class lever using one example.

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Human Levers

Saturday February 9, 2019

Levers are classified into three types: first class, second class, or third class. Their class is identified by the location of the load, the force moving the load, and the fulcrum. In this activity, you will learn about the types of levers and then use your body to make each type.

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Here’s what you need

- 1 body

Download Student Worksheet & Exercises

Here’s what you do

In a first class lever, the fulcrum is in the middle. The load and effort are on opposite sides with the fulcrum between them. A familiar example of a first class lever is a see saw.
A second class lever has the fulcrum on one end, the load in the middle, and the force on the end opposite the fulcrum. A wheelbarrow is a good example of a second class lever.
Lastly, a third class lever has a fulcrum on one end and the load on the opposite end. The force is applied in the middle in this type of lever. A golf club is an example of a third class lever.
Use the photos to identify the levers of each type in your body.

What’s going on?

Only read further if you have had an opportunity to identify the levers in the pictures. Spoilers below!

Your head moving up and down on your spine is an example of a first class lever. Your neck joint in the middle is the fulcrum, with load and effort on either side. In this example, load and effort switch depending on whether you are moving your head up or down.

Standing on tiptoe is an example of a second class lever where your toes are the fulcrum. The effort, or force, is in your heels – they are lifting your body up. And the resistance is located between your toes and heels.

This leaves us with bicep curls, which are an example of a third class lever. Your elbow serves as the fulcrum, the bicep is the force, and the weight in your hand on the end is the load.

Just for fun, did you know your knee is the largest joint in your whole body? It connects your femur, the largest bone, to the bones of your lower leg. Your smallest joints are the anvil, hammer, and stirrup in your inner ear.

Exercises

Draw a diagram of a first-class lever. Where in your body is this type of lever?
Draw a diagram of a third-class lever. Where will you find this?
Draw a diagram of a second-class lever. Can you give an example of this type of lever in the real world?

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Catapults

Saturday February 9, 2019

When you drop a ball, it falls 16 feet the first second you release it. If you throw the ball horizontally, it will also fall 16 feet in the first second, even though it is moving horizontally… it moves both away from you and down toward the ground. Think about a bullet shot horizontally. It travels a lot faster than you can throw (about 2,000 feet each second). But it will still fall 16 feet during that first second. Gravity pulls on all objects (like the ball and the bullet) the same way, no matter how fast they go.

What if you shoot the bullet faster and faster? Gravity will still pull it down 16 feet during the first second, but remember that the surface of the Earth is round. Can you imagine how fast we’d need to shoot the bullet so that when the bullet falls 16 feet in one second, the Earth curves away from the bullet at the same rate of 16 feet each second?

Answer: that bullet needs to travel nearly 5 miles per second. (This is also how satellites stay in orbit – going just fast enough to keep from falling inward and not too fast that they fly out of orbit.)

Catapults are a nifty way to fire things both vertically and horizontally, so you can get a better feel for how objects fly through the air. Notice when you launch how the balls always fall at the same rate – about 16 feet in the first second. What about the energy involved?

When you fire a ball through the air, it moves both vertically and horizontally (up and out). When you toss it upwards, you store the (moving) kinetic energy as potential energy, which transfers back to kinetic when it comes whizzing back down. If you throw it only outwards, the energy is completely lost due to friction.

The higher you pitch a ball upwards, the more energy you store in it. Instead of breaking our arms trying to toss balls into the air, let’s make a simple machine that will do it for us. This catapult uses elastic kinetic energy stored in the rubber band to launch the ball skyward.

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Here’s what you need:

9 tongue-depressor size popsicle sticks
four rubber bands
one plastic spoon
ping pong ball or wadded up ball of aluminum foil (or something lightweight to toss, like a marshmallow)
hot glue gun with glue sticks

Download Student Worksheet & Exercises

What’s going on? We’re utilizing the “springy-ness” in the popsicle stick to fling the ball around the room. By moving the fulcrum as far from the ball launch pad as possible (on the catapult), you get a greater distance to press down and release the projectile. (The fulcrum is the spot where a lever moves one way or the other – for example, the horizontal bar on which a seesaw “sees” and “saws”.)

Troubleshooting: These simple catapults are quick and easy versions of the real thing, using a fulcrum instead of a spring so kids don’t knock their teeth out. After making the first model, encourage kids to make their own “improvements” by handing them additional popsicle sticks, spoons, and glue sticks (for the hot glue guns).

If they get stuck, you can show them how to vary their models: glue a second (or third, fourth, or fifth) spoon onto the first spoon for multi-ammunition throws, increase the number of popsicle sticks in the fulcrum from 7 to 13 (or more?), and/or use additional sticks to lengthen the lever arm. Use ping pong balls as ammo and build a fort from sheets, pillows, and the backside of the couch.

Want to make a more advanced catapult?

This catapult requires a little more time, materials, and effort than the catapult design above, but it’s totally worth it. This device is what most folks think of when you say ‘catapult’. I’ve shown you how to make a small model – how large can you make yours?

This project lends itself well to taking data and graphing your results: you and your child can jot down the distance traveled along with time aloft with further calculations for high school students for velocity and acceleration. My university students would also calculate statistics, percent error, and more. My students also mapped out the material properties of the ‘cantilevered beam’ as well as model the popsicle stick as a spring (to determine the spring constant (k) for your calculations from Hooke’s Law). You can take this project as far as you want, depending on the interest and ability of kids.

Materials:

plastic spoon
14 popsicle sticks
3 rubber bands
wooden clothespin
straw
wood skewer or dowel
scissors
hot glue gun

Try different ball weights (ping pong, foil crumpled into a ball, whiffle balls, marshmallows, etc) and chart out the results: make a data table that shows what ball you tried and how far it went. You can also use a stopwatch to time how long your ball was in the air.

You can also graph your results: make a chart where you plot each data point on a graph that has distance on the vertical axis and time on the horizontal axis.

Advanced Teaching Tips: For high school and college-level physics classes, you can easily incorporate these launchers into your calculations for projectile motion. Offer students different ball weights (ping pong, foil crumpled into a ball, and whiffle balls work well) and chart out the results.

Exercises Answer the questions below:

How is gravity related to kinetic energy?
1. Gravity creates kinetic energy in all systems.
2. Gravity explains how potential energy is created.
3. Gravity pulls an object and helps its potential energy convert into kinetic energy.
4. None of the above
If you could use your catapult to launch your ball of foil into orbit, how high would it have to go?
1. Above the atmosphere
2. High enough to slingshot around the moon
3. High enough so that when it falls, the earth curves away from it
4. High enough so that it is suspended in empty space
Where is potential energy the greatest on the catapult?

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Pendulums

Saturday February 9, 2019

This is a very simple yet powerful demonstration that shows how potential energy and kinetic energy transfer from one to the other and back again, over and over. Once you wrap your head around this concept, you’ll be well on your way to designing world-class roller coasters.

For these experiments, find your materials:

some string
a bit of tape
a washer or a weight of some kind
set of magnets (at least 6, but more is better)

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Here’s what you do:

1. Make the string into a 2 foot or so length.

2. Tie the string to the washer, or weight.

3. Tape the other end of the string to a table.

4. Lift the weight and let go, causing the weight to swing back and forth at the end of the pendulum.

Download Student Worksheet & Exercises

Watch the pendulum for a bit and describe what it’s doing as far as energy goes. Some questions to think about include:

Where is the potential energy greatest?
Where is the kinetic energy greatest?
Where is potential energy lowest?
Where is kinetic energy lowest?
Where is KE increasing, and PE is decreasing?
Where is PE increasing and KE decreasing?
Where did the energy come from in the first place?

Remember, potential energy is highest where the weight is the highest.

Kinetic energy is highest were the weight is moving the fastest. So potential energy is highest at the ends of the swings. Here’s a coincidence, that’s also where kinetic energy is the lowest since the weight is moving the least.

Where’s potential energy the lowest? At the middle or lowest part of the swing. Another coincidence, this is where kinetic energy is the highest! Now, wait a minute…coincidence or physics? It’s physics right?

In fact, it’s conservation of energy. No energy is created or destroyed, so as PE gets lower KE must get higher. As KE gets higher PE must get lower. It’s the law…the law of conservation of energy! Lastly, where did the energy come from in the first place? It came from you. You added energy (increased PE) when you lifted the weight.

(By the way, you did work on the weight by lifting it the distance you lifted it. You put a certain amount of Joules of energy into the pendulum system. Where did you get that energy? From your morning Wheaties!)

Chaos Pendulum

For this next experiment, we’ll be using magnets to add energy into the system by having a magnetic pendulum interact with magnets carefully spaced around the pendulum. Watch the video to learn how to set this one up. You’ll need a set of magnets (at least one of them is a ring magnet so you can easily thread a string through it), tape, string, and a table or chair. Are you ready?

Exercises

Why can we never make a machine that powers itself over and over again?
1. Energy is mostly lost to heat.
2. Energy is completely used up.
3. Energy is unlimited, but is absorbed by neighboring air molecules.
4. None of these
In the pendulum, as kinetic energy increases, potential energy ______________.
1. Increases
2. Decreases
As potential energy decreases, kinetic energy _________________.
1. Increases
2. Decreases

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Mystery Toy

Saturday February 9, 2019

Note: Do the pendulum experiment first, and when you’re done with the heavy nut from that activity, just use it in this experiment.

You can easily create one of these mystery toys out of an old baking powder can, a heavy rock, two paper clips, and a rubber band (at least 3″ x 1/4″). It will keep small kids and cats busy for hours.

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Here’s what you get:

can with a lid
heavy rock or large nut
two paper clips
rubber band

You’ll need two holds punched through your container – one in the lid and the bottom. Thread your rubber band through the heavy washer and tie it off (this is important!). Poke the ends of the rubber band through one of the holes and catch it on the other side with a paper clip. (Just push a paper clip partway through so the rubber band doesn’t slip back through the hole.) Do this for both sides, and make sure that your rubber band is a pulled mildly-tight inside the can. You want the hexnut to dangle in the center of the can without touching the sides of the container.

Download Student Worksheet & Exercises

Now for the fun part… gently roll the can on a smooth floor away from you. The can should roll, slow down, stop, and return to you! If it doesn’t, check the rubber band tightness inside the can.

The hexnut is a weight that twists up the rubber band as the can rolls around it. The kinetic energy (the rolling motion of the can) transforms into potential (elastic) energy stored in the rubber band the free side twists around. The can stops (this is the point of highest potential energy) and returns to you (potential energy is being transformed into kinetic). The farther the toy is rolled the more elastic potential energy it stores.

Exercises

Explain in your own words two types of energy transfer:
True or false: All energy in a system is lost to heat.
1. True
2. False

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Go Go GO!!

Saturday February 9, 2019

This is a nit-picky experiment that focuses on the energy transfer of rolling cars. You’ll be placing objects and moving them about to gather information about the potential and kinetic energy.

We’ll also be taking data and recording the results as well as doing a few math calculations, so if math isn’t your thing, feel free to skip it.

Here’s what you need:

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a few toy cars (or anything that rolls like a skate)
a board, book or car track
measuring tape

The setup is simple. Here’s what you do:

1. Set up the track (board or book so that there’s a nice slant to the floor).

2. Put a car on the track.

3. Let the car go.

4. Mark or measure how far it went.

Download Student Worksheet & Exercises

As you lifted the car onto the track you gave the car potential energy. As the car went down the track and reached the floor the car lost potential energy and gained kinetic energy. When the car hit the floor it no longer had any potential energy only kinetic.

If the car was 100% energy efficient, the car would keep going forever. It would never have any energy transferred to useless energy. Your cars didn’t go forever did they? Nope, they stopped and some stopped before others. The ones that went farther were more energy efficient. Less of their energy was transferred to useless energy than the cars that went less far.

Where did the energy go? To heat energy, created by the friction of the wheels, and to sound energy. Was energy lost? NOOOO, it was only changed. If you could capture the heat energy and the sound energy and add it to the the kinetic energy, the sum would be equal to the original amount of energy the car had when it was sitting on top of the ramp.

For K-8 grades, click here to download a data sheet.

For Advanced Students, click here for the data log sheet. You’ll need Microsoft Excel to use this file.

Exercises

Where is the potential energy greatest?
Where is the kinetic energy greatest?
Where is potential energy lowest?
Where is kinetic energy lowest?
Where is KE increasing, and PE is decreasing?
Where is PE increasing and KE decreasing?

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Bobsleds

Saturday February 9, 2019

Bobsleds use the low-friction surface of ice to coast downhill at ridiculous speeds. You start at the top of a high hill (with loads of potential energy) then slide down a icy hill til you transform all that potential energy into kinetic energy. It’s one of the most efficient ways of energy transformation on planet Earth. Ready to give it a try?

This is one of those quick-yet-highly-satisfying activities which utilizes ordinary materials and turns it into something highly unusual… for example, taking aluminum foil and marbles and making it into a racecar.

While you can make a tube out of gift wrap tubes, it’s much more fun to use clear plastic tubes (such as the ones that protect the long overhead fluorescent lights). Find the longest ones you can at your local hardware store. In a pinch, you can slit the gift wrap tubes in half lengthwise and tape either the lengths together for a longer run or side-by-side for multiple tracks for races. (Poke a skewer through the rolls horizontally to make a quick-release gate.)

Here’s what you need:

aluminum foil
marbles (at least four the same size)
long tube (gift wrapping tube or the clear protective tube that covers fluorescent lighting is great)

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If you’re finding that the marbles fall out before the bobsled reaches the bottom of the slide, you need to either crimp the foil more closely around the marbles or decrease your hill height.

Check to be sure the marbles are free to turn in their “slots” before launching into the tube – if you’ve crimped them in too tightly, they won’t move at all. If you oil the bearings with a little olive oil or machine oil, your tube will also get covered with oil and later become sticky and grimy… but they sure go faster those first few times!

Download Student Worksheet & Exercises

Exercises Answer the questions below:

Potential energy is energy that is related to:
1. Equilibrium
2. Kinetic energy
3. Its system
4. Its elevation
If an object’s energy is mostly being used to keep that object in motion, we can say it has what type of energy?
1. Kinetic energy
2. Potential energy
3. Heat energy
4. Radiation energy
True or False: Energy is able to remain in one form that is usable over and over again.
1. True
2. False

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Roller Coasters

Saturday February 9, 2019

We’re going to build monster roller coasters in your house using just a couple of simple materials. You might have heard how energy cannot be created or destroyed, but it can be transferred or transformed (if you haven’t that’s okay – you’ll pick it up while doing this activity).

Roller coasters are a prime example of energy transfer: You start at the top of a big hill at low speeds (high gravitational potential energy), then race down a slope at break-neck speed (potential transforming into kinetic) until you bottom out and enter a loop (highest kinetic energy, lowest potential energy). At the top of the loop, your speed slows (increasing your potential energy), but then you speed up again and you zoom near the bottom exit of the loop (increasing your kinetic energy), and you’re off again!

Here’s what you need:

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marbles
masking tape
3/4″ pipe foam insulation (NOT neoprene and NOT the kind with built-in adhesive tape)

To make the roller coasters, you’ll need foam pipe insulation, which is sold by the six-foot increments at the hardware store. You’ll be slicing them in half lengthwise, so each piece makes twelve feet of track. It comes in all sizes, so bring your marbles when you select the size. The ¾” size fits most marbles, but if you’re using ball bearings or shooter marbles, try those out at the store. (At the very least you’ll get smiles and interest from the hardware store sales people.) Cut most of the track lengthwise (the hard way) with scissors. You’ll find it is already sliced on one side, so this makes your task easier. Leave a few pieces uncut to become “tunnels” for later roller coasters.

Read for some ‘vintage Aurora’ video? This is one of the very first videos ever made by Supercharged Science:

Download Student Worksheet & Exercises

Tips & Tricks

Loops Swing the track around in a complete circle and attach the outside of the track to chairs, table legs, and hard floors with tape to secure in place. Loops take a bit of speed to make it through, so have your partner hold it while you test it out before taping. Start with smaller loops and increase in size to match your entrance velocity into the loop. Loops can be used to slow a marble down if speed is a problem.

Camel-Backs Make a hill out of track in an upside-down U-shape. Good for show, especially if you get the hill height just right so the marble comes off the track slightly, then back on without missing a beat.

Whirly-Birds Take a loop and make it horizontal. Great around poles and posts, but just keep the bank angle steep enough and the marble speed fast enough so it doesn’t fly off track.

Corkscrew Start with a basic loop, then spread apart the entrance and exit points. The further apart they get, the more fun it becomes. Corkscrews usually require more speed than loops of the same size.

Jump Track A major show-off feature that requires very rigid entrance and exit points on the track. Use a lot of tape and incline the entrance (end of the track) slightly while declining the exit (beginning of new track piece).

Pretzel The cream of the crop in maneuvers. Make a very loose knot that resembles a pretzel. Bank angles and speed are the most critical, with rigid track positioning a close second. If you’re having trouble, make the pretzel smaller and try again. You can bank the track at any angle because the foam is so soft. Use lots of tape and a firm surface (bookcases, chairs, etc).

Troubleshooting Marbles will fly everywhere, so make sure you have a lot of extras! If your marble is not following your track, look very carefully for the point of departure – where it flies off.

-Does the track change position with the weight of the marble, making it fly off course? Make the track more rigid by taping it to a surface.
-Is the marble jumping over the track wall? Increase your bank angle (the amount of twist the track makes along its length).
-Does your marble just fall out of the loop? Increase your marble speed by starting at a higher position. When all else fails and your marble still won’t stay on the track, make it a tunnel section by taping another piece on top the main track. Spiral-wrap the tape along the length of both pieces to secure them together.

HOT TIPS for ULTRA-COOL PARENTS: This lab is an excellent opportunity for kids to practice their resilience, because we guarantee this experiment will not work the first several times they try it. While you can certainly help the kids out, it’s important that you help them figure it out on their own. You can do this by asking questions instead of rushing in to solve their problems. For instance, when the marble flies off the track, you can step back and say:

“Hmmm… did the marble go to fast or too slow?”

“Where did it fly off?”

“Wow – I’ll bet you didn’t expect that to happen. Now what are you going to try?”

Become their biggest fan by cheering them on, encouraging them to make mistakes, and try something new (even if they aren’t sure if it will work out).

Check out this cool roller coaster from one of our students!

Exercises

What type of energy does a marble have while flying down the track of a roller coaster?
What type of energy does the marble have when you are holding it at the top of the track?
At the top of a camel back hill, which is higher for the marble, kinetic or potential energy?
At the top of an inverted loop, which energy is higher, kinetic or potential energy?

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Special Science Teleclass: Physics of Motion

Saturday February 9, 2019

This is a recording of a recent live teleclass I did with thousands of kids from all over the world. I’ve included it here so you can participate and learn, too!

We’re going to cover energy and motion by building roller coasters and catapults! Kids build a working catapult while they learn about the physics of projectile motion and storing elastic potential energy. Let’s discover the mysterious forces at work behind the thrill ride of the world’s most monstrous roller coasters, as we twist, turn, loop and corkscrew our way through g-forces, velocity, acceleration, and believe it or not, move through orbital mechanics, like satellites. We’ll also learn how to throw objects across the room in the name of science… called projectile motion. Are you ready for a fast and furious physics class?

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Materials:

- click for worksheet
- marbles
- masking tape
- 3/4″ pipe foam insulation (NOT neoprene and NOT the kind with built-in adhesive tape)
- 9 popsicle sticks
- 4 rubber bands
- one plastic spoon
- ping pong ball
- hot glue gun with glue sticks

Key Concepts

Centripetal means ‘center-seeking’. It’s the force that points toward the center of the circle you’re moving on. When you swing the bucket around your head, the bottom of the bucket is making the water turn in a circle and not fly away. Your arm is pulling on the handle of the bucket, keeping it turning in a circle and not fly away. That’s centripetal force. Centrifugal force is equal and opposite to centripetal force. Centrifugal means ‘center-fleeing’, so it’s a force that’s in the opposite direction. The car pushing on you is the centripetal force.The push of your weight on the door is the REACTIVE centrifugal force, meaning that it’s only there when something’s happening. It’s not a real force that goes around pushing and pulling on its own.

What’s Going On?

Engines used to use an automatic feedback system called a centrifugal governor to regulate the speed. For example, if you’re mowing the lawn and you hit a dry patch with no grass, the blades don’t suddenly spin wildly faster… they get adjusted automatically by a feedback system so maintains the same speed for the blades, so matter how thick or thin the grass that your cutting is. You’ll find these also in airplanes to automatically adjust the pitch (or angle) of the propeller as it moves through the air. The pilot sets the intended speed, and the airplane has a governor that helps adjust the angle the blades make with the air to maintain this speed automatically, because the air density changes with altitude. It’s really important to know how much centrifugal force people experience, whether its in cars or roller coasters! In fact roller coaster loops used to be circular, but now they use clothoid loops instead to keep passengers happy during their ride so they don’t need nearly the acceleration that they’d need for a circular loop (which means less g-force so passengers don’t black out).

Here are more roller coaster maneuvers you can try out:

Loops: Swing the track around in a complete circle and attach the outside of the track to chairs, table legs, and hard floors with tape to secure in place. Loops take a bit of speed to make it through, so have your partner hold it while you test it out before taping. Start with smaller loops and increase in size to match your entrance velocity into the loop. Loops can be used to slow a marble down if speed is a problem.

Camel-Backs: Make a hill out of track in an upside-down U-shape. Good for show, especially if you get the hill height just right so the marble comes off the track slightly, then back on without missing a beat.

Whirly-Birds: Take a loop and make it horizontal. Great around poles and posts, but just keep the bank angle steep enough and the marble speed fast enough so it doesn’t fly off track.

Corkscrew: Start with a basic loop, then spread apart the entrance and exit points. The further apart they get, the more fun it becomes. Corkscrews usually require more speed than loops of the same size.

Jump Track: A major show-off feature that requires very rigid entrance and exit points on the track. Use a lot of tape and incline the entrance (end of the track) slightly while declining the exit (beginning of new track piece).

Troubleshooting

Marbles will fly everywhere, so make sure you have a lot of extras! If your marble is not following your track, look very carefully for the point of departure – where it flies off. For instance, when the marble flies off the track, you can step back and say:

“Hmmm… did the marble go to fast or too slow?”

“Where did it fly off?”

“Wow – I’ll bet you didn’t expect that to happen. Now what are you going to try?”

Become their biggest fan by cheering them on, encouraging them to make mistakes, and try something new (even if they aren’t sure if it will work out).

Questions to Ask

Does the track change position with the weight of the marble, making it fly off course? (You can make the track more rigid by taping it to a surface.)
Is the marble jumping over the track wall? (You can increase your bank angle – the amount of twist the track makes along its length.)
How can you make your marble zip through two loops at once?
How could you increase your marble speed?
Where would you put a tunnel? (Leave one piece of track uncut to use as a tunnel.)

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Inclined Plane

Saturday February 9, 2019

What’s an inclined plane? Jar lids, spiral staircases, light bulbs, and key rings. These are all examples of inclined planes that wind around themselves. Some inclined planes are used to lower and raise things (like a jack or ramp), but they can also used to hold objects together (like jar lids or light bulb threads).

Here’s a quick experiment you can do to show yourself how something straight, like a ramp, is really the same as a spiral staircase.

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Here’s what you need to find:

sheet of paper
short dowel or cardboard tube from a coat hanger
tape
ruler

Cut a right triangle out of paper so that the two sides of the right angle are 11” and 5 ½” (the hypotenuse – the side opposite the right angle – will be longer than either of these). Find a short dowel or use a cardboard tube from a coat-hanger. Roll the triangular paper around the tube beginning at the short side and roll toward the triangle point, keeping the base even as it rolls.

Notice that the inclined plane (hypotenuse) spirals up as a tread as you roll. Remind you of screw threads? Those are inclined planes. If you have trouble figuring out how to do this experiment, just watch the video clip below:

Download Student Worksheet & Exercises

Inclined planes are simple machines. It’s how people used to lift heavy things (like the top stones for a pyramid).

Here’s another twist on the inclined plane: a wedge is a double inclined plane (top and bottom surfaces are inclined planes). You have lots of wedges at home: forks, knives, and nails just name a few.

When you stick a fork in food, it splits the food apart. You can make a simple wedge from a block of wood and drive it under a heavy block (like a tree stump or large book) with a kid on top.

Exercises

What is one way to describe energy?
1. The amount of atoms moving around at any given moment
2. Electrons flowing from one area to another
3. The ability to do work
4. The square root of the speed of an electron
Work is when something moves when:
1. Force is applied
2. Energy is used
3. Electrons are lost or gained
4. A group of atoms vibrate
Name two simple machines:
Name one example of a simple machine:

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Seeing Sound Waves using Light

Saturday February 9, 2019

After you’ve completed this experiment, you can try making your own sound-to-light transformer as shown below. Using the properties of sound waves, we’ll be able to actually see sound waves when we aim a flashlight at a drum head and pick up the waves on a nearby wall.

Here’s what you need:

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empty soup can
balloon
small mirror
tape
scissors
hot glue gun
laser or flashlight

You will be adjusting the length of string of a pendulum until you get a pendulum that has a frequency of .5 Hz, 1 Hz and 2 Hz. Remember, a Hz is one vibration (or in this case swing) per second. So .5 Hz would be half a swing per second (swing one way but not back to the start). 1 Hz would be one full swing per second. Lastly, 2 Hz would be two swings per second. A swing is the same as a vibration so the pendulum must move away from where you dropped it and then swing back to where it began for it to be one full swing/vibration.
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“Advanced students: Download your Seeing Sound Waves using Light

Seeing Sound Waves

Saturday February 9, 2019

This section is actually a collection of the experiments that build on each other. We’ll be playing with sound waves, and the older students will continue on after this experiment to build speakers.

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Here’s what you need:

a radio or some sort of music player
a balloon
a mixing bowl
water
your parent’s permission

Download Student Worksheet & Exercises

1. Turn on your music player and turn it up fairly loud. (Tell your parents that it’s for science!)

2. Take a look at your speaker. You should be able to see it vibrating. If there’s a song with a lot of bass, you should really be able to see it moving.

3. Put your hand on the speaker. Can you feel the vibrations?

4. ASK YOUR PARENTS if you can carefully put a half-filled bowl of water on top of your speaker. You should be able to see the water vibrate.

Remember that sound is nothing more than vibrating molecules. All speakers do is get molecules of air to vibrate, creating longitudinal waves. They push air. Your eardrums vibrate just like the speakers do when the longitudinal waves of sound energy hit your ears.

How to Feel the Beat

1. Inflate the balloon. Get it fairly large.

2. Turn the music on loud (the more bass the better).

3. Put both hands lightly on the balloon.

4. Walk around the room holding the balloon lightly between your hands.

5. Try to feel the balloon vibrating.

6. Does the balloon vibrate more for low sounds or high sounds?

7. If you have a synthesizer (piano keyboard) you may want to try turning it up a bit and playing one note at a time. You should notice that the balloon vibrates more or less as you go up and down the musical scale. At very high notes, your balloon may not vibrate at all. We’ll talk more about why this happens later.

What’s causing the balloon to vibrate? Energy. Energy causes objects to move a distance against a force. The sound energy coming from the speakers is causing the balloon to vibrate. Your ear drums move in a very similar way to the balloon. Your ear drum is a very thin membrane (like the balloon) that is moved by the energy of the sound. Your ear drum, however, is even more sensitive to sounds than the balloon which is why you can hear sounds when the balloon is not vibrating. If you ear drum doesn’t vibrate, you don’t hear the sound.

What to do this experiment but no speakers?

Here’s another version of the same idea – I’ll bet you did this experiment when you were a small baby! You need: a mixing bowl (one of those metal bowls), something to hit it with ( a wooden spoon works well), and water.

1. Take the mixing bowl and put it on the table.

2. Smack it with the wooden spoon.

3. Listen to the sound.

4. Put your ear next to the bowl and try to hear how long the sound continues.

5. Now hit the bowl again.

6. Touch the bowl with your hand a second or two after you hit it. You should hear the sound stop. This is called dampening.

7. Now, for fun, fill the bowl with water up to an inch or so from the top.

8. Smack the bowl again and look very carefully at where the bowl touches the water.

9. When you first hit the bowl, you should see very small waves in the water.

I want you to notice two things here. Sound is vibration. When the bowl is vibrating, it’s making a sound. When you stop it from vibrating, it stops making sound. Any sound you ever hear, comes from something that is vibrating. It may have vibrated once, like a balloon popping. Or it may be vibrating consistently, like a guitar string.

The other thing I want you to notice is that you can actually see the vibrations. If you put water in the bowl, the tiny waves that are formed when you first hit the bowl are caused by the vibrating sides of the bowl. Those same vibrations are causing the sound that you hear.

If your mom’s worried about making a mess with water (and it’s not bath night tonight) then try this alternate experiment: you’ll need a mixing bowl, wooden spoon, and rubber bands.

1. Stretch a few rubber bands around the box or the bowl. If possible, use different thicknesses of rubber bands.

2. Strum the rubber bands.

3. Feel free to adjust how stretched the bands are. The more stretched, the higher the note.

4. Try plucking a rubber band softly.

5. Now pluck it fairly hard. The hard pluck should be louder.

Again I’d like you to notice three things here. Just like the last experiment, you should see that the sound is coming from the vibration. As long as the rubber band vibrates, you hear a sound. If you stop the rubber band from vibrating, you will stop the sound. Sound is vibration.

The second thing I’d like you to notice is that the rubber bands make different pitched sounds. The thinner the rubber band, or the tighter it’s stretched, the faster it vibrates. Another way to say “vibrating faster” is to say higher frequency. In sound, the higher the frequency of vibration, the higher the pitch of the note. The lower the frequency, the lower the pitch of the note. The average human ear can hear sound at as high a frequency as 20,000 Hz, and as low as 20 Hz. Pianos, guitars, violins and other instruments have strings of various sizes so that they can vibrate at different frequencies and make different pitched sounds. When you talk or sing, you change the tension of your vocal cords to make different pitches.

One last thing to notice here is what happened when you plucked the rubber band hard or softly. The rubber band made a louder noise the harder you plucked it right? Remember again that sound is energy. When you plucked that rubber band hard, you put more energy into it than when you plucked it softly. You gave energy (moved the band a distance against a force) to the rubber band. When you released the rubber band, it moved the air against a force which created sound energy. For sound, the more energy it has, the louder it is. Remember when we talked about amplitude a few lessons back? Amplitude is the size of the wave. The more energy a wave has the bigger it is. When it comes to sound, the larger the wave (the more energy it has) the louder it is. So when you plucked the rubber band hard (gave it lots of energy), you made a louder sound.

I said this in the beginning but I’ll repeat it here, hoping that now it makes more sense. When something vibrates, it pushes particles against a force (creates energy). These pushed particles create longitudinal waves. If the longitudinal waves have the right frequency and enough energy (loudness), your ear drum antennas will pick it up and your brain will translate the energy into what we call sound.

Exercises

What is sound?
How does the rubber band make different sounds?
What difference does it make how hard or soft you pluck the rubber bands?

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Harmonicas

Saturday February 9, 2019

Your voice is a vibration, and you can feel it when you place a hand on your throat when you speak. As long as there are molecules around, sound will be traveling though them by smacking into each other.

That’s why if you put an alarm clock inside a glass jar and remove the air, there’s no sound from the clock. There’s nothing to transfer the vibrational energy to – nothing to smack into to transfer the sound. It’s like trying to grab hold of fog – there’s nothing to hold on to.

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Here’s what you need:

two tongue depressors
three rubber bands, one at least 1/4″ wide
paper
tape

Download Student Worksheet & Exercises

What’s going on? The rubber band vibrates as you blow across the rubber band and you get a great sound. You can change the pitch by sliding the cuffs (this does take practice).

Troubleshooting: This project is really a variation on the Buzzing Hornets, but instead of using wind to vibrate the string, you use your breath. The rubber band still vibrates, and you can change the vibration (pitch) by moving the cuffs closer together or further apart. If the cuffs don’t slide easily, just loosen the rubber bands on the ends. You can also make additional harmonicas with different sizes of rubber bands, or even stack three harmonicas on top of each other to get unusual sounds.

If you can’t get a sound, you may have clamped down too hard on the ends. Release some of the pressure by untwisting the rubber bands on the ends and try again. Also – this one doesn’t work well if you spit too much – wet surfaces keep the rubber band from vibrating.

Exercises

What is sound?
What is energy?
What is moving to make sound energy?

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Buzzing Hornets

Saturday February 9, 2019

Sound is everywhere. It can travel through solids, liquids, and gases, but it does so at different speeds. It can rustle through trees at 770 MPH (miles per hour), echo through the ocean at 3,270 MPH, and resonate through solid rock at 8,600 MPH.

Sound is made by things vibrating back and forth, whether it’s a guitar string, drum head, or clarinet. The back and forth motion of an object (like the drum head) creates a sound wave in the air that looks a lot like a ripple in a pond after you throw a rock in. It radiates outward, vibrating it’s neighboring air molecules until they are moving around, too. This chain reaction keeps happening until it reaches your ears, where your “sound detectors” pick up the vibration and works with your brain to turn it into sound.

You can illustrate this principle using a guitar string – when you pluck the string, your ears pick up a sound. If you have extra rubber bands, wrap them around an open shoebox to make a shoebox guitar. You can also cut a hole in the lid (image left) and use wooden pencils to lift the rubber band off the surface of the shoebox.

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Materials:

index card
rubber band
3′ string
small piece of craft foam sheet OR a second index card
hot glue and glue sticks
tape

Download Student Worksheet & Exercises

Why is this happening? When you sling the hornet around, wind zips over the rubber band and causes it to vibrate like a guitar string… and the sound is focused (slightly) by the card. The card really helps keep the contraption at the correct angle to the wind so it continues to make the sound.

Troubleshooting: Most kids forget to put on the rubber band, as they get so excited about finishing this project that they grab the string and start slinging it around… and wonder why it’s so silent! Make sure they have a fat enough rubber band (about 3.5” x ¼ “ – or larger) or they won’t get a sound.

Variations include: multiple rubber bands, different sizes of rubber bands, and trying it without the index card attached. The Buzzing Hornet works because air zips past the rubber band, making it vibrate, and the sound gets amplified just a bit by the index card.

Exercises

What effect does changing the length of the string have on the pitch?
What vibrates in this experiment to create sound?
Why do we use an index card?

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Transverse and Longitudinal Waves

Saturday February 9, 2019

Since we can’t see soundwaves as they move through the air, we’re going to simulate one with rope and a friend. This will let you see how a vibration can create a wave. You’ll need at least 10 feet of rope (if you have 25 or 50 feet it’s more fun), a piece of tape (colored if you have it), a slinky, and a partner. Are you ready?

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1. Give one end of the rope to your partner.

2. Stretch the rope out so that it is a bit slack.

3. Now move your hand up and down. Feel free to do it several times in a row. Your partner should keep his or her hands as still as possible.

4. Watch the waves move from your hand to the other end of the rope.

5. Now let your partner create waves.

6. If you wish, you can try to time your vibrations and create waves with specific frequencies. A frequency of one Hertz is fairly easy to do (one rope shake per second). Can you create rope waves of higher frequencies? You may find that your arm gets tired pretty quickly!

Your hand is the vibrating particle. As your hand vibrated up and down, you moved the particles of the rope up and down. As those particles of rope vibrated, they vibrated the particles next to them. As they vibrated, they vibrated the particles next to them and so on and so forth. So the wave moved from your hand across the room. Did your hands move across the room. Nope, but the wave you created with your vibrating hand did.

This is the way energy travels. Why is the rope wave energy? Because the particles moved a distance against a force. Work was done on the particles. In fact, when you shook the rope, your energy from your body moved across the room with the wave and was transferred (moved to) your partner. Your partner’s hands could feel the energy you put into the rope in the first place. The work you did on the rope was transferred by the rope wave and did work on your partners hand. You have moved energy across the room!

Now… let’s add another element to this experiment…

Transverse Waves

1. Put a piece of (colored if possible) tape in about the middle of the rope.

2. Tie your rope to something or let your friend hold on to one end of it.

3. Now pull the rope so that it is a bit slack but not quite touching the floor.

4. Vibrate your arm. Move your arm up and down once and watch what happens.

5. Now, vibrate your arm a bunch of times (not too fast) and see the results. Notice the action of the tape in the middle of the rope.

What you’ve done is create a transverse wave. With a transverse wave, if the particle (in this case your hand) moves up and down, the wave will move to the left and/or right of the particle. The word perpendicular means that if one thing is up and down, the other thing is left and right. A transverse wave is a wave where the particle moves perpendicular to the medium. The medium is the material that’s in the wave. The medium in this case is the rope.

For example, in a water wave, the medium is the water. Your hand moved up and down, but the wave created by your hand moved across the room, not up. The wave moved perpendicular to the motion of your hand. Did you take a look at the tape? The tape represents a particle in the wave. Notice that it too, was going up and down. It was not moving along the wave. In any wave the particles vibrate, they do not move along the wave.

Longitudinal Waves

Now that you’ve seen a transverse wave, let’s take a look at a longitudinal wave. Here’s what you do:

1. Put a piece of tape on one slinky wire in the middle or so of the slinky.

2. Let your friend hold on to one end of the slinky or anchor the slinky to a chair or table.

3. Now stretch the slinky out, but not too far.

4. Quickly push the slinky toward your friend, or the table, and then pull it back to its original position. Did you see the wave?

5. Now do it again, back and forth several times and watch where the slinky is bunched up and where it’s spread out.

6. Notice the tape. What is it doing?

Here you made a longitudinal wave. A longitudinal wave is where the particle moves parallel to the medium. In other words, your hand vibrated in the same direction (parallel to the direction) the wave was moving in. Your vibrating hand created a wave that was moving in the same direction as the hand was moving in. Did you take a look at the tape? The tape was moving back and forth in the same direction the wave was going.

Do you see the difference between a transverse wave and a longitudinal wave? In a transverse waves the particles vibrate in a different direction (perpendicular) to the wave. In a longitudinal wave the particles vibrate in the same direction (parallel) to the wave.

What’s the Difference between Amplitude and Wavelength?

Here’s an easy way to get a feel for amplitude:

1. Put a piece of tape in about the middle of the rope.

2. Tie your rope to something or let your friend hold on to one end of it.

3. Now pull the rope so that it is a bit slack but not quite touching the floor.

4. Your friend should hold their hands as still as possible.

5. Vibrate your hand but only move it up and down about a foot or so. Have your partner pay attention to how that feels when the wave hits him or her.

6. Now, vibrate your hand but now move it up and down 2 or 3 feet. How does that feel to your partner?

7. Have your partner do the vibrating now and see what you feel.

You created two different amplitude waves. The first wave had a smaller amplitude than the second wave. What you and your partner should have felt was more energy the second time. The wave should have hit your hand with more energy when the wave had more amplitude.

Here’s a great way to visualize wavelength:

1. Tie your rope to something or let your friend hold on to it.

2. Now pull the rope so that it is a bit slack but not quite touching the floor.

3. Your friend should hold their hands as still as possible.

4. Now begin vibrating your hand fairly slowly. In this case, it works better if you move your hand in a circle.

5. Try to make a wavelength with the rope. In other words it will look like you’re playing jump rope.

6. Now try a one and a half wavelengths.

7. Can you get two or more wavelengths? You’ve really got to get your hand moving to get it.

In this image, the left wave is ONE wavelength, the middle is 1.5 wavelegnths, and the right is TWO wavelengths. See the difference?

Did you notice how the frequency of your hand determined the wavelength of the rope? The faster your hand, moved the more wavelengths you could get.
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What is Frequency?

Saturday February 9, 2019

In this experiment you will be adjusting the length of string of a pendulum until you get a pendulum that has a frequency of .5 Hz, 1 Hz and 2 Hz. Remember, a Hz is one vibration (or in this case swing) per second. So .5 Hz would be half a swing per second (swing one way but not back to the start). 1 Hz would be one full swing per second. Lastly, 2 Hz would be two swings per second. A swing is the same as a vibration so the pendulum must move away from where you dropped it and then swing back to where it began for it to be one full swing/vibration.

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You’ll need:

3 Foot Long String
A Weight that can be tied to the end of the string
A Timer or Stopwatch
Masking Tape
A Table or Chair
A Partner is helpful

“Advanced students: Download your What is Frequency?”

1. Tie your weight (the official name of the weight on the end is bob. Personally I’ve always preferred the name Shirley, but Bob it is.) to the end of the 3 foot string. If you’ve done the gravity lesson in the Mechanics set of lessons you’ll remember that the weight of the bob doesn’t matter. Gravity accelerates all things equally, so your pendulum will swing at the same speed no matter what the weight of the bob.

2. Tape the string to a table or chair or door jam. Make sure it can swing freely at about 3 feet of length.

3. I would recommend starting with 1 Hz. It tends to be the easiest to find. Then try .5 Hz and then 2 Hz.

4. The easiest way I’ve found to do this is to start the pendulum swinging and at the same time start the timer. Count how many swings you get in ten seconds.

5. Now, adjust the string. Make it longer or shorter and try again. When you get 10 swings in 10 seconds you got it! That’s one swing per second. You should be able to get quite close to one swing per second which is 1 Hz.

6. Now try to get .5 Hz. In this case you will get 5 swings in ten seconds when you find it. (A little hint, the string is pretty long here.)

7. Now speed things up a bit and see if you can get 2 Hz. Be prepared to count quick. That’s 2 swings a second or 20 swings in 10 seconds! (Another little hint, the string is quite short for this one.)

Did you get all three different frequency pendulums? It takes a while but my classes found it rather fun. You’ve created three different frequencies. 2 Hz being the fastest frequency. That was pretty fast right? Can you imagine something going at 10 Hz? 100 Hz? 1,000,000 Hz? I told you things were moving at outrageous speeds!

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Solar Cookies

Saturday February 9, 2019

Can you use the power of the sun without using solar cells? You bet! We’re going to focus the incoming light down into a heat-absorbing box that will actually cook your food for you.

Remember from Unit 9 how we learned about photons (packets of light)? Sunlight at the Earth’s surface is mostly in the visible and near-infrared (IR) part of the spectrum, with a small part in the near-ultraviolet (UV). The UV light has more energy than the IR, although it’s the IR that you feel as heat.

We’re going to use both to bake cookies in our homemade solar oven. There are two different designs – one uses a pizza box and the other is more like a light funnel. Which one works best for you?

Two large sheets of poster board (black is best)
Aluminum foil
Plastic wrap
Black construction paper
Cardboard box
Pizza box (clean!)
Tape & scissors
Reusable plastic baggies
Cookie dough (your favorite)

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Download Student Worksheet & Exercises

How does that work? Your solar cooker does a few different things. First, it concentrates the sunlight into a smaller space using aluminum foil. This makes the energy from the sun more potent. If you used mirrors, it would work even better!

You’re also converting light into heat by using the black construction paper. If you’ve ever gotten into car with dark seats, you know that those seats can get HOT on summer days! The black color absorbs most of the sunlight and transforms it into heat (which boosts the efficiency of your solar oven).

By strapping on a plastic sheet over the top of the pizza-box cooker, you’re preventing the heat from escaping and cooling the oven off. Keeping the cover clear allows sunlight to enter and the heat to stay in. (Remember the black stuff converted your light into heat?) If you live in an area that’s cold or windy, you’ll find this part essential to cooking with your oven!

Here’s another type of solar cooker that uses a cone design to focus the energy straight to your cookies!

Exercises Answer the questions below:

Name the type of heat energy that the sun provides:
1. Convection
2. Conduction
3. Radiation
4. Invection
What are some ways that the sun’s energy can be directly harnessed?
Name three of the different parts of the electromagnetic spectrum:

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How Can the Sun Be Used for Cooking?

Saturday February 9, 2019

Cooking involves heating food to bring about chemical changes. Sometimes foods are heated simply because the food tastes better warm than cold. In making tea, we sometimes heat water to help dissolve tea or help dissolve sugar if the tea is sweetened.

Normally the water used to make tea is heated on a range top or in a microwave oven. Using a range or microwave oven requires buying energy in the form of electricity or natural gas. Using a solar cooker does not require any energy costs because it uses a freely available renewable energy source-the sun.

A curved mirror in a bowl-like shape can focus reflected sunlight at a spot for cooking. A mirror about 1.5 meters (5 feet) across can generate a temperature of 177°C (350°F) and boil a liter of water in about fifteen minutes. In sunny areas of the world, solar cookers can be used instead of burning firewood for cooking.

Another way reflected and focused sunlight is used is to generate electricity. In southern California in 1982, a solar-thermal plant was built that can generate ten million watts of electrical power. This plant consists of 1,818 mirrored heliostats. A heliostat is a device that moves to track the sun across the sky and to reflect the sunlight at the same point. Each heliostat has twelve mirrors, and all the heliostats reflect sunlight to the same spot. The reflected light is directed at the top of a 90-meter (295-foot) tall tower. The concentrated sunlight is used to boil water and heat the steam up to 560° C (1,040 ° F). The steam turns a turbine that powers a generator to produce electricity.

One obvious disadvantage of solar-thermal plants is that they only operate when the sun is shining. The heat energy can be stored for a time by heating up a liquid or melting salt. Or the energy can be used to break water into hydrogen and oxygen. The hydrogen can then be stored and burned later to produce water and release energy.
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Materials

Three clear, clean plastic cups
Two small tea bags
Aluminum foil
Watch or clock
Measuring cup
Water
Two spoons
White sheet of paper
Plastic pan (4 inches deep and 12 inches across is a convenient size but other sizes can be used)

Download Student Worksheet & Exercises

Procedure

You will need to do this experiment on a warm, sunny day.

Use two sheets of aluminum foil and place them crosswise to completely cover the bottom and sides of a plastic pan. Try to arrange the aluminum foil so that it is smooth and curved like a bowl. The aluminum foil will help to reflect the solar energy and concentrate the light and heat toward the center of the pan. Place this aluminum covered pan outside in a warm, sunny spot where the sunlight will shine directly on it.

Add one cup of water to each of two plastic cups. The water you add to the cups should be neither hot nor cold, but about temperature. Place one cup of water in the middle of the pan. Turn the empty plastic cup upside down and place it on top of this cup. Leave this “solar cooker” undisturbed for one hour. The other cup of water should remain inside.

After one hour, gently place one tea bag in each of the water-filled cups. Wait ten minutes and then lift the tea bag out of each cup. Using a spoon, stir each cup of tea. Place both cups of tea on a white piece of paper and look down on the two cups to compare their darkness. Put your finger in each cup of tea to compare their temperatures.

Observations

Which cup of tea is a darker color? Which cup of tea is warmer?

Discussion

You should find that the water left in the “solar cooker” is darker and warmer than the water left in the shade. The darker color indicates that more tea has gone into or dissolved in the warmer water.

Other Things to Try

Place your “solar cooker” in the sun as in this experiment, but place one plastic cup upside down in the middle of the pan. Put a pat of margarine or butter on top of this cup. Will the sun melt this butter? How long does it take to melt? Repeat this activity with a piece of soft cheese and determine if the solar heater will melt the cheese. In a more carefully made solar cooker, the reflective surfaces are angled to focus a large amount of sunlight in one spot and the temperatures obtained are much higher than in your cooker.

Set one cup of water in your “solar cooker.” Set a second cup of water in the sunshine and leave both cups for one hour. Use a thermometer to check the temperature of each cup of water. Does your “solar cooker” help focus the sun’s rays and increase the temperature?

Exercises Answer the questions below:

What type of solar energy are we seeing in this experiment?
1. Solar fusion
2. Solar voltaic
3. Solar thermal
4. Radiation potential
Name two ways that the earth’s systems depend on the sun:
What is one advantage of solar thermal energy? What is one disadvantage?
1. Advantage:
2. Disadvantage:

Marshmallow Roaster

Saturday February 9, 2019

Do you like marshmallows cooked over a campfire? What if you don’t have a campfire, though? We’ll solve that problem by building our own food roaster – you can roast hot dogs, marshmallows, anything you want. And it’s battery-free, as this device is powered by the sun.

NOTE: This roaster is powerful enough to start fires! Use with adult supervision and a fire extinguisher handy.

If you’re roasting marshmallows, remember that they are white – the most reflective color you can get. If you coat your marshmallows with something darker (chocolate, perhaps?), your marshmallow will absorb the incoming light instead of reflecting it.

Here’s what you need to get:

7×10” page magnifier (Fresnel lens)
Cardboard box, about a 10” cube
Aluminum foil
Hot glue, razor, scissors, tape
Wooden skewers (BBQ-style)
Chocolate, marshmallows, & graham crackers

Here’s what you do:

Download Student Worksheet & Exercises

How does it do that? The Fresnel lens is a lot like a magnifying glass. In Unit 9, we learned how convex lenses are thicker in the middle (you can feel it with your fingers). A Fresnel lens (first used in the 1800s to focus the beam in a lighthouse) has lots of ridges you can feel with your fingers. It’s basically a series of magnifying lenses stacked together in rings (like in a tree trunk) to magnify an image.

The best thing about Fresnel lenses is that they are lightweight, so they can be very large (which is why light houses used these designs). Fresnel lenses curve to keep the focus at the same point, no matter close your light source is.

The Fresnel lens in this project is focusing the incoming sunlight much more powerfully than a regular hand held magnifier. But focusing the light is only part of the story with your roaster. The other part is how your food cooks as the light hits it. If your food is light-colored, it’s going to cook slower than darker (or charred) food. Notice how the burnt spots on your food heat up more quickly!

Scientifically Dissecting a Marshmallow

Plants take in energy (from the sun), water, and carbon dioxide (which is carbon and oxygen) and create sugar, giving off the oxygen. In other words: carbon + water + energy = sugar

In this experiment, we will reverse this equation, by roasting a marshmallow, which is mostly sugar.
When you roast your marshmallow, first notice the black color. This is the carbon.
Next notice the heat and light given off. These are two forms of energy.
Finally, put the roasting marshmallow if a mason jar. Notice that condensation forms on the sides. This is the water.

So, by roasting the marshmallow, we showed: sugar = carbon + water + energy!

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Can the Sun Be Used to Heat Water?

Saturday February 9, 2019

The energy of sunlight powers our biosphere (air, water, land, and life on the earth’s surface). About 50 percent of the solar energy striking the earth is converted to heat that warms our planet and drives the winds. About 30 percent of the solar energy is reflected directly back into space. The water cycle (evaporation of water followed by rain or snow) is powered by about 20 percent of the solar energy.

Some of the sunlight that reaches the earth is used by plants in photosynthesis. Plants containing chlorophyll use photosynthesis to change sunlight to energy. Since these green plants form the base of the food chain, all plants and animals depend on solar energy for their survival.

When the sun is overhead, about 1,000 watts of solar power strike 1 square meter (10.8 square feet) of the earth’s surface. Using solar cells, this solar energy can be converted to electricity. However, because sunlight cannot be converted completely to electricity, it takes at least a square meter of area to gather enough sunlight to run a 100-watt light bulb.

Solar energy is still more expensive than other methods of generating electricity. However, the cost of solar electricity has greatly decreased since the first solar cells were developed in 1954.

It has been proposed that panels of solar cells on satellites in orbit above the earth could convert solar energy to electricity twenty-four hours a day. These huge solar power satellites could convert electrical energy to microwaves and then beam these microwaves to Earth. At the earth’s surface, tremendous fields covered with antennas could convert the microwave energy back to electricity.

It would take thousands of astronauts many years to build such a complicated system. However, there are many practical uses of solar energy in use today. These uses include heating water, heating and cooling buildings, producing electricity from solar cells, and using rain and snow from the water cycle to power electrical generators at dams.

In the following experiments, you will examine the use of solar energy in heating water, .cooking foods, concentrating sunlight, and producing electricity.
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Materials

Paint brush
Thermometer (outdoor type)
Newspaper
Aluminum foil
Water
Large, plastic glass
Empty aluminum 12-ounce (355 milliliter) soft drink can
Black paint or spray paint (flat, not shiny)

Download Student Worksheet & Exercises

Procedure
Go outside and spread a sheet of newspaper on the ground. Place an empty aluminum soft drink can on the newspaper. Have an adult help you paint the outside of the aluminum can. You can use a brush and can of paint or spray paint. Be sure to use paint that is suitable for a metal surface. The paint should give you a flat (not shiny) surface. Be sure not to get the paint on anything but the can and newspaper. After painting, set the can where the paint can dry overnight.

You will need to do the rest of this experiment on a warm, sunny day. Partially fill a large, plastic glass with cool tap water. Check the temperature of the water with a thermometer. Pour the water from the plastic glass into the painted black can, completely filling the can. Pour out any extra water remaining in the plastic glass. Cover the can’s opening with a small piece of aluminum foil about the size of a quarter.

Set the black can outside in a sunny spot. Pick a place where the sun will shine on the can all day. (You do not want the can to be in the shade.)

After the can of water has been in the sunshine for about four hours, pour the water into the large, plastic glass. Check the temperature of the water with the thermometer. Feel the outside of the can.

Observations

What was the temperature of the cool tap water when it was first placed into the black can? What is the temperature of the water after it was heated in the can for four hours? Does the outside of the can feel hot?

Discussion

You should find a significant increase in the temperature of the water that was left in the black can during the day. The tap water initially may be about 21°C (70°F), but after the water has been heated inside the can, the temperature should rise to more than 38°C (100°F). The exact temperature you achieve in your miniature, solar water heater (black can) will depend on your location and the time of year. However, you should find that the water temperature will go much higher than the temperature of the outside air.

The electromagnetic radiation from the sun includes ultraviolet, visible, and infrared radiation. Ultraviolet radiation is the type of sunlight that causes tanning of skin. Visible radiation is the type of sunlight we see with our eyes. Infrared radiation is the type of sunlight that we feel as heat when the sun is shining on our skin. All these forms of solar radiation have energy associated with them.

When solar energy from the sun’s electromagnetic radiation strikes a black surface, solar energy is converted to heat energy and the surface is warmed. Other colors will absorb solar energy, but lightly colored surfaces tend to reflect the light, while darker colors absorb the solar energy. You may have noticed this difference if you ever walked barefoot on a dark road on a hot summer day.

Direct solar energy is not hot enough for cooking. The higher temperatures required for cooking or for changing water to steam require concentrating the energy of sunlight with mirrors or lenses. However, directly absorbed solar energy is hot enough for heating homes and producing hot water with little or no energy costs.

When we turn on a hot water faucet at a sink, water is taken from a hot water tank. In industrialized countries, we usually heat water using electricity or natural gas and store the hot water in this insulated tank. However, around the world, there are millions of solar heaters used for heating water.

Solar water heaters use a black metal plate covered with insulated glass. These solar heaters are usually placed on rooftops to receive the maximum amount of sunlight. Water flows through tubes beneath the black metal plates. Solar energy heats the black metal plates and the water passing in tubes underneath the plates. The heated water is piped to a storage tank, where it is kept until needed. If the location of the solar heater is not consistently sunny, then an auxiliary heater-using electricity or natural gas-is sometimes used to heat the water.

Other Things to Try

Repeat this experiment covering the black can with a large glass jar. This glass should help trap the heat and make the water get even hotter. What is the maximum temperature you can get with this type of solar heater?

Repeat this experiment and check the temperature of the water each half hour for three hours during the middle of the day. Quickly check the temperature of the water, then return the water to the black metal can. Write down the time that you checked the water, and next to the time, write down the temperature. How long does it take for the water to reach the maximum water temperature?

Repeat this experiment with an unpainted can and a painted can. After one hour, how do the temperatures of the water in each can compare?

Repeat this experiment on a cloudy day. Does the water in the can get as hot without sunshine?

Exercises

The solar energy that hits the earth is responsible for what proportion of the energy on our planet?
1. Nearly all of it
2. About 50%
3. 25%
4. None of these
Name one way that the physical earth uses the earth’s energy:
True or false: Solar power is generally less expensive than other forms of power.
1. True
2. False

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Solar Car

Saturday February 9, 2019

Solar energy (power) refers to collecting this energy and storing it for another use, like driving a car. The sun blasts 174 x 1015 watts (which is 174,000,000,000,000,000 watts) of energy through radiation to the earth, but only 70% of that amount actually makes it to the surface. And since the surface of the earth is mostly water, both in ocean and cloud form, only a small fraction of the total amount makes it to land.

A solar cell converts sunlight straight into electricity. Most satellites are powered by large solar panel arrays in space, as sunlight is cheap and readily available out there. While solar cells seem ‘new’ and modern today, the first ones were created in the 1880s, but were a mere 1% efficient. (Today, they get as high as 35%.) A solar cell’s efficiency is a measure of how much sunlight the cell converts into electrical energy.

We’re going to use solar cells and the basic ideas from Unit 10 (Electricity & Robotics) to build a solar-powered race car. You’ll need to find these items below. Note – if you have trouble locating parts, check the shopping list for information on how to order it straight from us.

Solar cell
Solar motor
Foam block (about 6” long)
Alligator clip leads
2 straws (optional)
2 wooden skewers (optional)
4 milk jug lids or film can tops
Set of gears, one of which fits onto your motor shaft (most solar motor kits come with a set), or rip a set out of an old toy

Here’s what you do:

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Download Student Worksheet & Exercises

How does a solar cell work? Solar cells are usually made of silicon. Sunlight is made of packets of energy called photons (we covered this in Unit 9). When photons hit the silicon, one of three things can happen: the photons can pass straight through the silicon if they have a low enough energy; they can get reflected off the surface; or (and this is the fun part) they get absorbed and the electrons in the silicon get knocked out of their shell.

Once knocked out of orbit, the free electrons start flowing through the silicon to create electricity. The solar cells are structured is such a way as to keep the electricity flowing only in one direction. The electron flow created is DC current (refer to Unit 10).

The solar cells you can buy from stores require huge amounts of energy in creating the solar cell, which is the primary downside. You need high temperatures, big vacuum pumps, and lots of people to make a set of solar cells. However, if we focus just on the physics of the solar cell, then we can easily create our own solar battery and other solar cell projects using household items. While these cells won’t look as spiffy as the ones from the store, they still produce electricity from sunlight.

Using the same solar cell, you can also build a Wind Turbine and a Solar Boat.

Exercises Answer the questions below:

Most solar cells are made of what material?
1. Hydrogen
2. Aluminum
3. Silicon
4. Titanium
Name one benefit of solar cells and one drawback of using them for electricity.
1. Benefit:
2. Drawback:
Electrical current begins flowing when:
1. Sunlight hits an atom
2. Electrons are knocked out of orbiting atoms
3. Protons get charged
4. An atom’s nucleus splits

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Solar Boat

Saturday February 9, 2019

Does it really matter what angle the solar cell makes with the incoming sunlight? If so, does it matter much? When the sun moves across the sky, solar cells on a house receive different amounts of sunlight. You’re going to find out exactly how much this varies by building your own solar boat.

Solar motor
Solar cell
Foam block (about 6” long)
Alligator clip leads
Propeller (you can rip one off an old small personal fan or old toy, or find them at hobby stores)

Here’s what you do:

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Download Student Worksheet & Exercises

1. Attach the wires of the solar cell to the motor (one to each motor terminal).

2. Attach the propeller to your motor. If the shaft won’t fit, drill out the center hole. If the hole is too large, use a tiny dab of hot glue on the shaft tip to secure the propeller into place.

3. Stand out in the sun. How do you need to hold your solar cell to make the propellers pin the fastest?

4. Position the motor on a block of foam so that the propeller hangs off the edge and is free to rotate. Hot glue the motor into place, being careful not to get any hot glue near any vents in your motor.

5. Hot glue your solar cell to the foam block. You might want to check the final position in sunlight before attaching it.

6. Optional: Wire up a simple switch (from Unit 10) using paperclips and brass fasteners so you can easily turn your power on and off.

How does it do that? If you want to learn about how solar cells create electricity, click here.

Going further: Using the same solar cell, you can also build a Wind Turbine and a Solar Car.

Exercises Answer the questions below:

What kind of electricity comes from a battery and photovoltaic cell?
1. Nuclear
2. Voltaic
3. Electrochemical
4. Ionized
Electricity is another name for the free flow of:
1. Protons
2. Quarks
3. Electrodes
4. Electrons
True or false: Ions are attracted to the same charge.
1. True
2. False
Do solar panels work in cloudy climates?
1. Yes
2. No

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Can Electricity Be Made From Sunlight?

Saturday February 9, 2019

The solar cell you are using for this experiment is made from the element silicon. Silicon solar cells consist of two thin wafers of treated silicon that are sandwiched together. The treated silicon is made by first melting extremely pure silicon in a special furnace. Tiny amounts of other elements are added which produce either a small positive or negative electrical charge.

Usually boron is added to produce a positive charge and phosphorus is added to produce a negative charge. The addition of these other elements to pure silicon to produce an electrical charge is called doping.

After being doped, the molten silicon is allowed to cool. As it cools, the doped silicon grows into a large crystal from which very thin wafers are cut. A wafer cut from a large crystal of silicon doped with boron is called the positive or P-layer because it has a positive charge. A wafer cut from a large crystal of silicon doped with phosphorous is called the negative or N-layer.

To make a solar cell, a positive wafer (P-layer) and a negative wafer (N-layer) are sandwiched together. This causes the P-layer to develop a slight positive charge, and the N-layer to develop a slight negative charge. The solar cell is connected to a circuit by wires leading from the P-layer and the N-layer. When light falls on the surface of the cell, electrons are made to move from one layer to the other. Thus, a current of electricity flows through the circuit.

The first solar cells provided electrical power for space satellites and vehicles. Satellites and space vehicles are still big users of solar cells. Solar cells are now being used to provide electrical power for calculators and similar devices, weather stations in remote areas, oil-drilling platforms, and remote communication relay stations.

The best silicon cells convert only a small portion of the sunlight striking the cells into electricity. The efficiency of solar cells is about 15 percent. This means that 15 percent of the sunlight that strikes the cell is converted into electrical energy. The sunlight that is not converted into electricity either reflects off the surface of the cell or is converted into heat energy.
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Materials

Silicon solar cell
Two wires with alligator clips on each end of the wires
Earphone or headset for a portable radio
AA-size battery

Download Student Worksheet & Exercises

Procedure

For this experiment you will need a silicon solar cell. Small silicon solar cells are inexpensive and can be purchased at many electronic supply stores.

This experiment should be done on a bright, sunny day.

Examine the metal shaft on the part of the earphone or headset that is inserted into a portable radio. You will notice that just above the tip of the shaft there is a plastic spacer. Clip on one of the wires below this spacer. Then clip on the other wire above this spacer.

To test that the wires are properly connected to the earphone or headset, take the unconnected ends of the two wires and touch them to an AA-size battery. One wire should touch the positive end of the battery, while the other should touch the negative end of the battery. Place the earphone or headset to your ear. If your connections are made correctly, you should hear a crackling sound in the earphone or headset. If you do not hear a crackling sound, check your connections carefully.

Take the earphone or headset, with wires attached, and the solar cell outside into the sunshine. Ask a friend to join you. Your friend can help you hold the solar cell.

Place the earphone or headset to your ear. Ask your friend to hold one of the flat sides of the solar cell facing the sun. The two flat sides of the solar cell are different. In this experiment, you will determine which flat side must face the sun for the cell to generate electricity.

While your friend holds one of the flat sides of the solar cell facing· the sun, you hold one of the alligator clips on the side of the cell facing the sun. At the same time touch the other alligator clip to the opposite side of the cell. As you hold the alligator clips to the cell, avoid blocking the sunlight striking the solar cell.

Ask your friend to turn the solar cell over so that the side that was not facing the sun before now does. Touch a clip to the two sides of the solar cell.

After determining which side of the solar cell needs to face the sun to make a crackling sound in your earphone or headset, ask your friend to hold that side toward the sun. Touch the two alligator clips to each side of the solar cell. Move the alligator clip touching the bottom of the solar cell around the bottom side to keep making the crackling sound in your earphone or headset. Next block the sunlight striking the solar cell.

Observations

Describe the difference between the two sides of the solar cell. Which side must be facing the sun to cause crackling in the earphone or headset when you touch the clips to the solar cell? What happens to the crackling sound when you block the sunlight from striking the solar cell?

Discussion

When you examine your silicon solar cell, you will notice that the two flat sides of the cell are different. One side should have a silvery color, while the other side should appear dark. You should determine in this experiment that one side of the solar cell needs to face the sun for you to hear a strong crackling sound in the earphone or headset. The crackling sound is electricity, generated by the solar cell, passing through the earphone or headset.

Other Things to Try

Repeat this experiment on a cloudy day. Do you still hear a crackling sound in the earphone or headset? If you do hear a crackling sound, is it quieter than on a bright, sunny day?

Is there enough light in a room to cause the solar cell to make electricity? Try it yourself and see.

Exercises

If two electrodes become activated by a current, which way will the ions flow?
1. To the electrode of the same charge
2. To the electrode of the opposite charge
3. None of the above
What type of energy source is the solar panel most closely related to?
1. Biofuel
2. Chemical battery
3. Nuclear reactor
4. Plant energy
The solar cell’s efficiency is not very good. How much of its energy is converted into electricity?
1. 50 %
2. 80%
3. 30%
4. Less than all of these
Name one common use for solar cells:

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Do Plants Store Energy?

Saturday February 9, 2019

A peanut is not a nut, but actually a seed. In addition to containing protein, a peanut is rich in fats and carbohydrates. Fats and carbohydrates are the major sources of energy for plants and animals.

The energy contained in the peanut actually came from the sun. Green plants absorb solar energy and use it in photosynthesis. During photosynthesis, carbon dioxide and water are combined to make glucose. Glucose is a simple sugar that is a type of carbohydrate. Oxygen gas is also made during photosynthesis.

The glucose made during photosynthesis is used by plants to make other important chemical substances needed for living and growing. Some of the chemical substances made from glucose include fats, carbohydrates (such as various sugars, starch, and cellulose), and proteins.

Photosynthesis is the way in which green plants make their food, and ultimately, all the food available on earth. All animals and nongreen plants (such as fungi and bacteria) depend on the stored energy of green plants to live. Photosynthesis is the most important way animals obtain energy from the sun.

Oil squeezed from nuts and seeds is a potential source of fuel. In some parts of the world, oil squeezed from seeds-particularly sunflower seeds-is burned as a motor fuel in some farm equipment. In the United States, some people have modified diesel cars and trucks to run on vegetable oils.

Fuels from vegetable oils are particularly attractive because, unlike fossil fuels, these fuels are renewable. They come from plants that can be grown in a reasonable amount of time.
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Materials

Shelled peanut
Small pair of pliers
Match or lighter
Sink

Download Student Worksheet & Exercises

Procedure

ASK AN ADULT TO HELP YOU WITH THIS EXPERIMENT. DO NOT DO THIS EXPERIMENT BY YOURSELF. The fuel from the peanut can flare up and burn for a longer time than expected.

Close the drain in the kitchen sink. Fill the sink with water until the bottom of the sink is just covered.

Using a small pair of pliers, hold the peanut over the sink containing water. Ask an adult to hold the flame of a lit match or lighter directly under the peanut. When the peanut starts to burn, the lit match or lighter can be removed.

Allow the peanut to burn for one minute. MAKE SURE AN ADULT REMAINS PRESENT AND MAKE SURE TO HOLD THE PEANUT OVER THE SINK. To extinguish the burning peanut, drop it into the water. After you have extinguished the peanut, allow it to cool and then examine it carefully.

Observations

How long does it take for the peanut to start to burn? Does the peanut burn with a clean flame or a sooty flame? What color is the flame? What color does the peanut turn when it burns? Did the size of the peanut change after it has burned for several minutes?

Discussion

You should find that the peanut ignites and burns after a lit match or lighter is held under it for a few seconds. Although you only let the peanut burn for one minute as a safety measure, the peanut would burn for many minutes.

In this experiment, when the peanut burns, the stored energy in the fats and carbohydrates of the peanut is released as heat and light. When you eat peanuts, the stored energy in the fats and carbohydrates of the peanut is used to fuel your body.

Other Things to Try

Hold one end of a piece of uncooked spaghetti in a pair of pliers. Ask an adult to hold the flame of a lit match or lighter under the other end of the spaghetti. When the spaghetti starts to burn, place it in an aluminum pie pan that is in the sink. Make sure to extinguish the burning spaghetti with water when you are finished with the experiment. How does the burning of the spaghetti compare with the burning of the peanut?

Exercises

What is the process called where plants get food from the sun?
1. Osteoporosis
2. Photosynthesis
3. Chlorophyll
4. Metamorphosis
Where does all life on the planet get its food?
List two ways that we could use the energy in a peanut:

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Salty Battery

Saturday February 9, 2019

Using ocean water (or make your own with salt and water), you can generate enough power to light up your LEDs, sound your buzzers, and turn a motor shaft. We’ll be testing out a number of different materials such as copper, aluminum, brass, iron, silver, zinc, and graphite to find out which works best for your solution.

This project builds on the fruit battery we made in Unit 8. This experiment is for advanced students.

The basic idea of electrochemistry is that charged atoms (ions) can be electrically directed from one place to the other. If we have a glass of water and dump in a handful of salt, the NaCl (salt) molecule dissociates into the ions Na+ and Cl-.

When we plunk in one positive electrode and one negative electrode and crank up the power, we find that opposites attract: Na+ zooms over to the negative electrode and Cl- zips over to the positive. The ions are attracted (directed) to the opposite electrode and there is current in the solution.

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Here’s what you need:

water
salt
vinegar (distilled white)
bleach IMPORTANT: WEAR GOGGLES!
glass container (like a cleaned out jam jar)
electrodes
real silverware (not stainless)
shiny nail (galvanized)
large paper clip
dull nail (iron)
wood screws (brass)
copper pennies minted before 1982 (or a short section of copper pipe)
graphite from inside a pencil (use a mechanical pencil refill)
2 alligator wires
digital multimeter

Download Student Worksheet & Exercises

Here’s what you do:

Fill a cup with water, adding a teaspoon of salt, a teaspoon of distilled white vinegar, and a few drops of bleach. NOTE: BE very careful with bleach! Cap it and store as soon as you’ve added it to the cup.
Find two of the following materials: copper*, aluminum*, brass, iron, silver, zinc, graphite (* indicates the ones that are easiest to start with – use a copper penny and a piece of aluminum foil). Attach an alligator clip lead to each one and dunk into your cup. Make sure these two metals DO NOT TOUCH in the solution.
You’ve just made a battery! Test it with your digital volt meter and make a note of the voltage reading. Connect the multimeter in series to read the current (remove a clip from the metal and clip it to one test probe, and attach the other test probe to the metal. Make sure you’re reading AMPS, not VOLTS when you note the reading for current).
Test out different combinations of materials and note which gives the highest voltage reading for you. Is it enough to light an LED? Buzzer? Motor? What if you made two of these and connected them in series? Three? Four?

Electrochemistry studies chemical reactions that generate a voltage and vice versa (when a voltage drives a chemical reaction), called oxidation and reduction (redox) reactions. When electrons are transferred between molecules, it’s a redox process.

Fruit batteries use electrolytes (solution containing free ions, like salt water or lemon juice) to generate a voltage. Think of electrolytes as a material that dissolves in water to make a solution that conducts electricity. Fruit batteries also need electrodes made of conductive material, like metal. Metals are conductors not because electricity passes through them, but because they contain electrons that can move. Think of the metal wire like a hose full of water. The water can move through the hose. An insulator would be like a hose full of cement – no charge can move through it.

You need two different metals in this experiment that are close, but not touching inside the solution. If the two metals are the same, the chemical reaction doesn’t start and no ions flow and no voltage is generated – nothing happens.

Exercises

Which combination gives the highest voltage?
What happens if you use two strips of the same material?
What would happen if we used non-metal strips?

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Can a Battery Be Used to Store Energy?

Saturday February 9, 2019

A battery is a device that produces electrical energy from a chemical reaction. Another name for a battery is voltaic cell. Voltaic means to make electricity.

Most batteries contain two or more different chemical substances. The different chemical substances are usually separated from each other by a barrier. One side of the barrier is the positive terminal of the battery and the other side of the barrier is the negative terminal. When the positive and negative terminals of a battery are connected to a circuit, a chemical reaction takes place between the two different chemical substances that produces a flow of electrons (electricity).

When a battery is producing electricity, one of the chemical substances in the battery loses electrons. These electrons are then gained by the other chemical substance.

A battery is designed so that the electrons lost by one chemical substance are made to flow through a circuit, such as a flashlight lamp, before being gained by the other chemical substance. A battery will produce a flow of electrons until all of the chemical substances involved in the chemical reaction are completely used.

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Materials

Earphone or headset for a portable radio
Small piece of aluminum foil
Tomato paste or tomato ketchup
New, shiny penny
Two wires with alligator clips on each end of the wires
Plate
AA-size battery
Spoon

Download Student Worksheet & Exercises

Procedure

Examine the metal shaft of the part of the earphone or headset that is inserted into a portable radio. You will notice that just below the tip of the shaft there is a plastic spacer. Clip on one of the wires below this spacer. Then clip on the other wire above this spacer.

To test that the wires are properly connected to the earphone or headset, take the unconnected ends of the two wires and touch them to an AA-size battery. One wire should touch the positive end of the battery, while the other is touching the negative end of the battery. Place the earphone or headset to your ear. If your connections are made correctly, you should hear a crackling sound in the earphone or headset. If you do not hear a crackling sound, check your connections carefully.

Place a small piece of aluminum foil, about five inches (13 centimeters) square, on a small plate. Using a spoon, make a puddle of tomato juice on the aluminum foil. The puddle of tomato juice should be slightly larger than a penny. Next, place a new, shiny penny face down in the puddle of tomato juice.

Using the alligator clip, attach one of the wires connected to the earphone to one of the edges of the aluminum foil. Take the end of the other wire and touch the alligator clip to the penny. Move the alligator clip over the penny.

Observations

Do you hear a crackling sound when you touch the alligator clips to the penny in the puddle of tomato juice? What do you hear when you move the alligator clip over the penny? What do you hear when you stop touching the penny with the alligator clip?

Discussion

In this experiment you made a simple battery with a penny, aluminum foil, and tomato juice. You completed a circuit with your battery by touching one of the wires attached to the earphone or headset to the penny, while touching the other wire to the aluminum foil. When you completed the circuit, a flow of electrons was produced by your battery. The crackling sound you heard was caused by the earphone or headset converting electrical energy from your battery into sound energy.

In your battery, the aluminum in the aluminum foil loses electrons. The other part of the reaction is more complex. Either the acid in the tomato juice or copper ions (that form when the copper metal in the penny reacts with the acid in the tomato juice) gain the electrons lost by the aluminum.

The main types of batteries are known as primary and secondary batteries. Dry cell batteries, like the ones used in flashlights and portable radios, are primary batteries. Another important primary battery is the mercury battery. Mercury batteries are typically small and flat. They are used to power cameras, watches, hearing aids, and calculators.

An advantage of primary batteries is that they are generally inexpensive. One disadvantage is that they cannot be recharged. When the chemical substances in the primary batteries are used up, the battery is dead.

Lead storage batteries and nickel-cadmium (NiCad) batteries are examples of secondary batteries. Car batteries are lead storage batteries. Flashlight batteries that are rechargeable are NiCad batteries. Secondary batteries are more expensive than primary batteries. However, unlike primary batteries, lead storage batteries and NiCad batteries can be recharged repeatedly.

Other Things to Try

Repeat this experiment using other coins such as a dime, nickel, or quarter. Do any of these coins cause a louder crackling sound in the earphone or headset?

Repeat this experiment using a nail instead of a coin. Can you make a battery with other juices? To find out, repeat this experiment with other juices such as lemon and orange juice. What do you observe?

Exercises

Fill in the blank: A battery produces ___________________ energy from _________________________ energy.
Another name for a battery is:
1. Solar array
2. Voltaic cell
3. Nuclear reactor
4. Fusion cell
As one chemical loses electrons, what happens to the other chemical?
1. It loses electrons
2. It gains electrons
3. Nothing
4. It decomposes
When will a battery run out?
1. When its batteries run out
2. When its chemicals are used up
3. When all the electrons are gone
4. When the bunny stops drumming

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Special Science Teleclass: Renewable & Alternative Energy

Saturday February 9, 2019

This is a recording of a recent live teleclass I did with thousands of kids from all over the world. I’ve included it here so you can participate and learn!

Discover the world of clean, renewable energy that scientists are developing today! Explore how they are harnessing the energy of tides and waves, lean how cars can run on just sunlight and water, tour a hydroelectric power plant, visit the largest wind farms on the planet, and more! You’ll learn how streets are being designed to generate electricity, how teenagers are making jet fuel from pond scum in their garage, and how 70 million tons of salt can provide free, clean energy 24 hours a day forever! During class, you’ll learn how to bake solar cookies, magni-fry marshmallows and do the experiment with light Einstein won a Nobel prize for that is the basis of all photovoltaic energy today.

Materials:

One cup each: hot (not boiling), cold, and room temperature water
Cardboard box, shoebox size or larger.
Aluminum foil
Plastic wrap (like Saran wrap or Cling wrap)
Hot glue, razor, scissors, tape
Wooden skewers (BBQ-style)
Black construction paper
Cookie dough (your favorite kind!)
Chocolate, large marshmallows, & graham crackers if you want to make s’mores! If not, try just the large marshmallow.
Large page magnifier (also called a Fresnel lens, found at drug stores or places that also sell reading glasses, or at Amazon.com)
This worksheet

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What’s Going On?

For the main experiment:

The Fresnel (“FRAY-nell”) lens is a lot like a magnifying glass. Convex lenses (like a handheld magnifier) are thicker in the middle – you can actually feel it with your fingers. A Fresnel lens was first used in the 1800s to focus the beam in a lighthouse. It has lots of ridges you can feel with your fingers. It’s basically a series of magnifying lenses stacked together in rings (like in a tree trunk) to magnify an image.

Questions to Ask

What other kinds of food can you roast with your setup?
Does a white marshmallow or chocolate-covered marshmallow cook faster? Why?
Does it matter what angle you point your roaster at?
Will it work with an indoor light?
Why do you need the foil? Can you skip it?
Do we have to use a Fresnel lens? What about a handheld magnifier – would that work?

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Microscopes and Telescopes

Saturday February 9, 2019

Hans Lippershey was the first to peek through his invention of the refractor telescope in 1608, followed closely by Galileo (although Galileo used his telescope for astronomy and Lippershey’s was used for military purposes). Their telescopes used both convex and concave lenses.

A few years later, Kepler swung into the field and added his own ideas: he used two convex lenses (just like the ones in a hand-held magnifier), and his design the one we still use today. We’re going to make a simple microscope and telescope using two lenses, the same way Kepler did. Only our lenses today are much better quality than the ones he had back then!

You can tell a convex from a concave lens by running your fingers gently over the surface – do you feel a “bump” in the middle of your hand magnifying lens? You can also gently lay the edge of a business card (which is very straight and softer than a ruler) on the lens to see how it doesn’t lay flat against the lens.

Your magnifier has a convex lens – meaning the glass (or plastic) is thicker in the center than around the edges. The image here shows how a convex lens can turn light to a new direction using refraction. You can read more about refraction here.

A microscope is very similar to the refractor telescope with one simple difference – where you place the focus point. Instead of bombarding you with words, let’s make a microscope right now so you can see for yourself how it all works together. Are you ready?

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How to Make a Microscope

Materials:

2 hand held magnifiers
dollar bill
penny

Here’s what you do: Hold one magnifying glass in each hand. Focus one lens on a printed letter or small object. Add the second lens above the first, so you can see through both. Move the lens toward and away from you until you bring the letter into clear focus again. You just made a microscope! The lens closest to your eye is the EYEpiece. The lens closest to the object is the OBJECTive. The image here is of the objective part of a compound microscope. The different silver tubes have different sizes of lenses, each with a different magnification, so the same scope can go from 40X to 1,000X with the flip of a lens.

How do I determine magnification power for my microscope? Simply multiply the powers of your optics together to get the power of magnification. If you’re using one lens at 10X and the other at 4X, then the combined effect is 40X. You’ll usually find the power rating stamped in tiny writing along the magnifier.

So now you’ve made a microscope. How about a telescope? Is it really a lot different?

The answer is no. Simply hold your two lenses as you would for a microscope, but focus on a far-away object like a tree. You just made a simple telescope… but the image is upside-down!

We don’t fully understand why, but every time we teach this class, kids inevitably start catching things on fire. We think it’s because they want to see if they really can do it – and sure enough, they find out that they can! Just do it in a safe spot (like a leaf on concrete) if that’s something you want to do. Click here for a detailed instructional video on how to do this safely.

How do I connect the flaming shrubbery back to the main optics lesson? Ask your child why the leaf catches on fire… and when the shrug, you can lead them around to a discussion about focus points of a lens. It’s hard for kids to visualize the light lines through a lens, so you can shine a strong light through a fine-tooth comb as shown in the image above. Use clear gelatin (or Jell-O) shapes as your “lenses” and shine your rays of light through it. If your room is dark enough, you’ll get the image shown above.

The point where all the lines intersect is where things catch fire, as the energy is most concentrated at this point. Note how the lines flip after the focus point – this is why the telescope images are inverted. The microscope image is not flipped because you’ve placed the image (and/or your eye) before the focus point. Play around with it and find out where the focus point is. Slide your lenses along a yardstick to easily measure distances.

How to Make a Telescope

Materials:

2 hand held magnifiers
window

Want to experiment further? Then click for the Optical Bench experiment and also sneak a peek at the Advanced Telescope Building experiment where you will learn about lenses, refractor, and newtonian telescopes.

Ready to buy your own professional-quality instrument that will last you all the way through college? Click here for our recommendations on microscopes, telescopes, and binoculars.
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Slide Preparation: Heat Fixes

Saturday February 9, 2019

Make sure you’ve completed the How to Use a Microscope and also the Wet Mount and Staining activities before you start here!

If you tried looking at animal cells already, you know that they wiggle and squirm all over the place. And if you tried looking when using the staining technique, you know it only makes things worse.

The heat fix technique is the one you want to use to nail your specimen to the slide and also stain it to bring out the cell structure and nuclei. This is the way scientists can look at things like bacteria.

You’re going to need your microscope, slides, cover slips, eyedropper, toothpicks or tweezers, candle and matches (with adult help), stain (you can use regular iodine or Lugol’s Stain), sugar, yeast, and a container to mix your specimen in. Here’s what you do:

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Download Student Worksheet & Exercises

1. Fill your container with warm water. Add about a tablespoon of yeast (one packet is enough) along with a teaspoon of sugar. The warm water activates the yeast and the sugar feeds it. You should see a foam top form in about 10 minutes.

2. Using your eyedropper, grab a bit of your sample (you want the liquid, not the foam) and place a drop on a fresh slide. Spread the drop out with a toothpick. You want to smear it into a thin layer.

3. Light the candle (with adult help). Heat the slide in the flame by gently waving it back and forth. Don’t stop it in the flame, or you’ll get black soot on the underside of the slide and possibly crack it because the glass heats up and expands too fast. You also don’t want to cook the yeast, as it will destroy what you want to look at. Just wave it around to evaporate the water.

4. Add a drop of iodine (or stain) to the slide. Wait 15 seconds.

5. Rinse it under water. (You can optionally stain it again if you find it’s particularly difficult to see your specimen, but make sure to look at it first before repeat staining.)

6. Place a drop of water (use a clean eyedropper) on the specimen and add the cover slip.

7. Lower the stage to the lowest setting and rotate the nose piece to the lowest magnification power.

8. Place the slide on the stage in your clips.

9. Focus by looking through the eyepiece and slowly turning the coarse adjustment knob. When you’re close to focus, switch to the fine adjustment knob until it pops into sharp view.

10. Adjust the light level to get the greatest contrast so you can see better.

11. Move the slide around (this is where a mechanical stage is wonderful to have) until you spot something interesting. Place it in the center of your field of view, and switch magnification power to find a great view (not too close, not to far away). Adjust your focus as needed.

12. Open your science notebook and draw a circle. Sketch what you see (don’t forget the title and mag power!)

NOTE: What other things can you look at? You can scrape the inside of your cheek with a toothpick and smear it on a fresh slide, take a mold sample from last week’s leftovers in the fridge, or…? Have fun!

Exercises

Why do we use heat fixes?
Briefly describe how to do a heat fix.
What is a specimen that needs a heat fix?

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Slide Preparation: Staining

Saturday February 9, 2019

Make sure you’ve completed the How to Use a Microscope and also the Wet Mount activities before you start here!

If your critter is hard to see, you can use a dye to bring out the cell structure and make it easier to view. There are lots of different types of stains, depending on what you’re looking at.

The procedure is simple, although kids will probably stain not only their specimens, but the table and their fingers, too. Protect your surfaces with a plastic tablecloth and use gloves if you want to.

We’re going to use an iodine stain, which is used in chemistry as an indicator (it turns dark blue) for starch. This makes iodine a good choice when looking at plants. You can also use Lugol’s Stain, which also reacts with starch and will turn your specimen black to make the cell nuclei visible. Methylene blue is a good choice for looking at animal cells, blood, and tissues.

In addition to your specimen, you’ll need to get out your slides, microscope, cover slips, eye dropper, tweezers, iodine (you can use regular, non-clear iodine from the drug store), and a scrap of onion. If you can find an elodea leaf, add it to your pile (check with your local garden store). Here’s what you do:

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Download Student Worksheet & Exercises

1. Fill a container with water and add a small piece of elodea leaf and onion. You’ll want the onion to be a thin slice, no more than a quarter of an inch thick.

2. Practice making a wet mount first. Put a fresh slide on the table. Using tweezers, pull off a thin layer of onion (use a layer from the middle, not the top) and place it on your slide. Gently stretch out the wrinkles (use a toothpick or tweezers) and add a small drop of water and cover with a cover slip. Take a peek at what your specimen looks like on low power – do you notice it’s hard to see much? Draw what you see in your notebook.

3. Now increase the power and look again. Draw a new sketch in your notebook.

4. Now we’re going to highlight the cell structure using iodine. Lugol’s is also iodine, but the regular brown stuff from the drug store works, too. Grab a bottle of the one you’re going to use.

5. To stain the specimen, we’re going to add the stain to one side of the cover slip and wick away the water from the other side. Use a folded piece of tissue paper and touch it lightly to one side of the cover slip as you add a single drop of stain to the other side. When the stain has flowed through the entire specimen, take a peek and draw what you see in a a fresh circle.

6. Do the same thing with the elodea leaf. And anything else plant-based from your backyard. Or refrigerator. Draw what you see and don’t forget to label it with a title and power of magnification!

Exercises

Why do we use a wet mount slide?
Give one example of a specimen that would use a wet mount slide?
How do you prepare a wet mount slide?
Why do we stain specimens?
Give one example of a specimen that would use a stain.
What type of stain can we use (give at least one example).

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Preparing a Wet Mount Slide

Saturday February 9, 2019

Make sure you've completed the How to Use a Microscope activity before you start here!

Anytime you have a specimen that needs water to live, you'll need to prepare a wet mount slide. This is especially useful for looking at pond water (or scum), plants, protists (single-cell animals), mold, etc. When you keep your specimen alive in their environment, you not only get to observe it, but also how it eats, lives, breathes, and interacts in its environment.

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The first thing you need to do is collect your pond water. Make sure it has lots of good stuff in it! You'll need a 20mL sample. Once you have it, place it on a table along with your microscope, slides, cover slips, tweezers, and dropper. If you're using Protoslo (if critters are too fast, this slow them down for easier viewing), get that out, too. Open up your science notebook, draw a bunch of circles for drawing borders, and then watch this video:

Download Student Worksheet & Exercises

1. Place a slide on the table.

2. Fill the eyedropper with pond water and place a drop on the slide.

3. Place the edge of the cover slip on the pond water drop, holding the other edge up at an angle. Slowly lower the end down so that the drop spreads out. You want a very thin film to lay on the slide without any air bubbles or excess water squirting out. If you go have bubbles, gently press down on the cover slip to squish them out or start over.

4. Take time practicing this - you want the water only under the coverslip. Dab away excess water that's not under the slide with a paper towel.

5. Lower the stage to the lowest setting and rotate the nose piece to the lowest magnification power.

6. Place the slide on the stage in your clips.

7. Focus by looking through the eyepiece and slowly turning the coarse adjustment knob. When you're close to focus, switch to the fine adjustment knob until it pops into sharp view.

8. Adjust the light level to get the greatest contrast so you can see better.

9. Move the slide around (this is where a mechanical stage is wonderful to have) until you spot something interesting. Place it in the center of your field of view, and switch magnification power to find a great view (not too close, not to far away). Adjust your focus as needed.

8. Open your science notebook and draw a circle. Sketch what you see (don't forget the title and mag power!)

9. When you're done, lower the stage all the way and insert a new slide... and repeat. Find at least six things to look at. We're not only learning how to look and draw, but hammering a habit of how to handle the scope properly, so do as many as you can find.

NOTE: If the critters you're looking at move too fast, add a drop of Protoslo to the edge of your slide to slow them down (by numbing them). The Protoslo will work its way under the cover slip.

Exercises

Why do we use a wet mount slide?
Give one example of a specimen that would use a wet mount slide?
How do you prepare a wet mount slide?
Why do we stain specimens?
Give one example of a specimen that would use a stain.
What type of stain can we use (give at least one example).

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Preparing a Dry Mount Slide

Saturday February 9, 2019

Make sure you’ve completed the How to Use a Microscope activity before you start here!

This is simplest form of slide preparation! All you need to do is place it on the slide, use a coverslip (and you don’t even have to do that if it’s too bumpy), and take a look through the eyepiece. No water, stains, or glue required.

You know that this is the mount type you need when your specimen doesn’t require water to live. Good examples of things you can try are cloth fibers (the image here is of cotton thread at 40X magnification), wool, human hair, salt, and sugar. It’s especially fun to mix up salt and sugar first, and then look at it under the scope to see if you can tell the difference.

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Here’s what you do:

1. Pull a hair from your head and lay it on a slide. If it’s super-curly, use a bit of tape at either end, stretching it along the length of the slide. Keep the tape near the ends so it doesn’t come into your field of view when you look through the microscope.

2. Lower the stage to the lowest setting and rotate the nose piece to the lowest magnification power.

3. Place the slide on the stage in your clips.

4. Focus the hair by looking through the eyepiece and slowly turning the coarse adjustment knob. When you’re close to focus, switch to the fine adjustment knob until it pops into sharp view.

5. Open your science notebook and draw a circle. Sketch what you see (don’t forget the title and mag power!)

6. When you’re done, lower the stage all the way and insert a new slide… and repeat. Find at least six things to look at. We’re not only learning how to look and draw, but hammering a habit of how to handle the scope properly, so do as many as you can find.

Don’t forget to check the windowsills for interesting bits. Use baby food jars or film canisters to collect your specimens in and keep them safe until you need them.

TIP: If you want to keep your specimen on the slide for a couple of months, use a drop of super glue and lay a coverslip down on top, pressing gently using a toothpick (not your fingers) to get the air bubbles out. Let dry.

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How to Use a Microscope: Optics, Observing, and Drawing Techniques

Saturday February 9, 2019

How do the lenses work to make objects larger? We’re going to take a closer look at optics, magnification, lenses, and how to draw what you see with this lesson. Here’s a video to get you started:

Here’s what you do:

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1. Take a look at the eyepiece of your microscope. Do you see a number followed by an X? That tells you the magnification of your microscope. If it’s a 10X, then it will make objects appear ten times larger than usual.

2. Peek at the objective lenses. They’re on the nose of the microscope, and there’s usually 3 or 4 of them. Do you see the little numbers printed on the side of the lenses, also followed by an X? Find the one that says 4. if you look through just that lens by itself, objects will appear 4 times as large. However, it’s in a microscope, so you’re actually looking through two lenses when you use the microscope. What that means is that you need to multiply this number by the eyepiece magnification (in our example, it’s 4 * 10 = 40) to get the total power of magnification when you use the microscope on this power setting. It’s 40X when you use the 10X eyepiece and 4X objective. So objects are going to appear 40 times larger than in real life.

3. Practice these with your microscope – here are the settings on my microscope – help me fill out the table to figure out how to set the lenses for the different magnification powers:

Eyepiece	Objective	Total Magnification
10X	4X
10X		100X
	40X	400X
10X		1000X

Questions to Ask:

1. What does this table above look like for your microscope?

2. Your microscope may have come with an additional eyepiece. If so, add it to your table and figure out the range of magnification you have.

3. What is your highest power of magnification? Set it now.

4. List three possible combination of eyepiece and objective lenses if the power of magnification is 100X.

Learning to Look

Do how do you use this microscope thing, anyway? Here’s how you prepare, look, and adjust so you can get a great view of the micro world:

Download Student Worksheet & Exercises

1. Carefully cut a single letter (like an “a” or “e”) from a printed piece of paper (newspaper works well).

2. Use your tweezers to place the small letter on a slide and place a coverslip over it (be careful with these – they are thin pieces of glass that break easily!) If your letter slides around, add a drop of water and it should stick to the slide.

3. Lower the stage to the lowest setting using the coarse adjustment knob (look at the stage when you do this, not through the eyepiece).

4. Place your slide in the stage clips.

5. Turn the diaphragm to the largest hole setting (open the iris all the way).

6. Move the nose so that the lowest power objective lens is the one you’re using.

7. Bring the stage up halfway and peek through the eyepiece.

8. If you’re using a mirror, rotate the mirror as you look through the eyepiece until you find the brightest spot. You’ll probably only see a fuzzy patch, but you should be able to tell bright from dim at this point.

9. Use the coarse adjust to move the stage slowly up to bring it into rough focus. If you’ve lowered the stage all the way in step 7, you’ll see it pop into focus easily. (Be careful you don’t ram the stage into the lens!)

10. Use the fine adjust to bring it into sharp focus. What do you see?

Drawing What You See

Learning to sketch what you see is important so that the view is useful to more than just you. Here’s the easy way to do it: get a water glass and trace around the rim on a sheet of paper with your pencil. This gives you a nice, large circle that represents your scope’s field of view (what you see when you look into the microscope). Now you’re ready for the next step:

1. Draw a picture of that the letter looks like under the lowest power setting in your first circle and label it ‘right side up’. Then give the slide a half turn and draw another picture in a new circle. Label this one ‘upside-down’.

2. If you’re using a mechanical stage (which we highly recommend), twist one of the knobs so that the slide physically moves to the right as you look from the side (not through the eyepiece) of the microscope. If you’re using stage clips, just nudge the slide to the right with your finger. Now peek through the eyepiece as you move the slide to the right – which way does your letter move?

3. Now do the same for the other direction – make the slide move toward you. Which way does the letter appear to move when you look through the eyepiece?

4. What effect do the two lenses have on the letter image as you move it around? (Need a hint? Look back at the Microscope Optics Lesson from Unit 9)

Look back at your two drawings above. Let’s make them so they are totally useful, the way scientists label their own sketches. We’re going to add a border, title, power of magnification, and more to get you in the habit of labeling correctly. Here’s how you do it:

Border You need to frame the picture so the person looking at it knows where the image starts and ends. Use a water glass to help make a perfect circle every time. When I sketch at the scope, I’ll fill an entire page with circles before I start so I can quickly move from image to image as I switch slides.

Title What IS it? Paramecia, goat boogers, or just a dirty slide? Let everyone (including you!) know what it is by writing exactly what it is. You can use bold lettering or underline to keep it separate from any notes you take nearby.

Magnification Power This is particularly useful for later, if you need to come back and reference the image. You’ll be quickly and easily able to duplicate your own experiment again and again, because you know how it was done.

Proportions This is where you need to draw only what you see. Don’t make the image larger or smaller – just draw exactly what you see. If it’s got three legs and is squished in the upper right corner, then draw that. Most people draw their image smaller than it really is when viewed through the eyepiece. If it helps, mentally divide the circle into four quarters and look at each quarter-circle and make it as close to what you see as you can.

Exercises

Why do we use microscopes?
What’s the highest power of magnification on your microscope? Lowest?
Where are the two places you should NEVER touch on your microscope?
Fill in the blanks with the appropriate word to describe care and cleaning of your microscope:fingers lowest handsarm toilet paper legs dust cover
1. Pick up the microscope with two ________. Always grab the _________with one hand and the _______(base) with the other.
3. Don’t touch the lenses with your _________. The oil will smudge and etch the lenses. Use an optical wipe if you must clean the lenses. Steer clear of ____________ and paper towels – they will scratch your lenses.
5. When you’re done with your scope for the day, reset it so that it’s on the _________ power of magnification and lower the stage to the lowest position. Cover it with your __________ or place it in its case.
What things must be present on your drawing so others know what they’re looking at?
What’s the proper way to use the coarse adjustment knob so you don’t crack the objective lens?
List three possible combination of eyepiece and objective lenses if the power of magnification is 100X.
Briefly describe how to dry mount a slide.
How could you view a copper penny with your microscope?

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Anatomy of the Microscope

Saturday February 9, 2019

Nose? Objective? Stage? What kind of class is this? Well, some of the names may sound a bit odd, but this video will show you what they are and how they are used. As you watch the video, touch the corresponding part of your microscope to get a feel for how it works.

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NOTE: Be very careful NOT to raise the stage too high or you’ll crack the objective lens! Always leave a space between the stage and the lens!! Anytime you use the coarse adjustment knob, always look at the stage itself, NOT through the eyepiece (for this very reason). When you use the fine adjustment knob, that’s when you look through the eyepiece.

Care and Cleaning

1. Pick up the microscope with two hands. Always grab the arm with one hand and the legs (base) with the other.

2. Don’t touch the lenses with your fingers. The oil on your fingers will smudge and etch the lenses. Use an optical wipe if you must clean the lenses. Steer clear of toilet paper and paper towels – they will scratch your lenses.

3. When you’re done with your scope for the day, reset it so that it’s on the lowest power of magnification and lower the stage to the lowest position. Cover it with your dust cover or place it in its case.

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Microwhat?

Saturday February 9, 2019

Welcome to our unit on microscopes! We’re going to learn how to use our microscope to make things appear larger so we can study them more easily. Think about all the things that are too small to study just with your naked eyeballs: how many can you name?

Let’s start from the inside out – before you haul out your own microscope, we’re going to have a look at what it can do. I’ve already prepared a set of slides for you below. Take out a sheet of paper and jot down your guesses – here’s how you do it:

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What is it?

Take a peek and see if you can figure out what each one is. Record your guess on a piece of paper. Don’t spend more than 90 seconds on each one. If you’re working with others, have everyone write down their answers individually, and then work together and discuss each one. Come up with a final group conclusion what’s on each slide before peeking at the answers.

Need answers? Hover your mouse over each slide to reveal the title.

Indoor Rain Clouds

Making indoor rain clouds demonstrates the idea of temperature, the measure of how hot or cold something is. Here’s how to do it:

Take two clear glasses that fit snugly together when stacked. (Cylindrical glasses with straight sides work well.)

Fill one glass half-full with ice water and the other half-full with very hot water (definitely an adult job – and take care not to shatter the glass with the hot water!). Be sure to leave enough air space for the clouds to form in the hot glass.

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Place the cold glass directly on top of the hot glass and wait several minutes. If the seal holds between the glasses, a rain cloud will form just below the bottom of the cold glass, and it actually rains inside the glass! (You can use a damp towel around the rim to help make a better seal if needed.)

Materials:

glass of ice water
glass of hot water (see video)
towel
adult help

Download Student Worksheet & Exercises

Bottling Clouds

On a stormy, rainy afternoon, try bottling clouds — using the refrigerator! Here’s what you do: Place an empty, clean 2-liter soda bottle in the fridge overnight. Take it out and get an adult to light a match, letting it burn for a few seconds, then drop it into the bottle. Immediately cap the bottle and watch what happens (you should see smoke first, then clouds forming inside). Squeeze the sides of the bottle. The clouds should disappear. When you release the bottle, the clouds should reappear. Materials:

2L soda bottle
rubbing alcohol
bicycle pump
car tire valve (drill a 1/2 inch hole through a 2L soda bottle cap and pull the valve gently through with pliers)

Advanced Idea: You can substitute rubbing alcohol and a bicycle pump for the matches to make a more solid-looking cloud. Swirl a bit of rubbing alcohol around inside the bottle, just enough to coat the insides, and then pour it out. Cap your bottle with a rubber stopper fitted with a needle valve (so the valve is poking out of the bottle), and apply your pump. Increase the pressure inside the bottle (keep a firm hand on the stopper or you’ll wind up firing it at someone) with a few strokes and pull out the stopper quickly. You should see a cloud form inside.

What’s going on? Invisible water vapor is all around us, all the time, but they normally don’t stick together. When you squeezed the sides of the bottle, you increased the pressure and squeezed the molecules together. Releasing the bottle decreases the pressure, which causes the temperature to drop. When it cools inside, the water molecules stick to the smoke molecules, making a visible cloud inside your bottle.

Did you know that most drops of water actually form around a dust particle? Up in the sky, clouds come together when water vapor condenses into liquid water drops or ice crystals. The clouds form when warm air rises and the pressure is reduced (as you go up in altitude). The clouds form at the spot where the temperature drops below the dew point.

The alcohol works better than the water because it evaporates faster than water does, which means it moves from liquid to vapor more easily (and vividly) than regular old water.

Questions to ask:

How many times can you repeat this?
Does it matter what size the bottle is?
What if you don’t chill the bottle?
What if you freeze the bottle instead?

Exercises

Which combination made it rain the best? Why did this work?
Draw your experimental diagram, labeling the different components:
Add in labels for the different phases of matter. Can you identify all three states of matter in your experiment?

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Seasons

Friday February 8, 2019

One common misconception is that the seasons are caused by how close the Earth is to the Sun. Today you get to do an experiment that shows how seasons are affected by axis tilt, not by distance from the Sun. And you also find out which planet doesn’t have sunlight for 42 years.

The seasons are caused by the Earth’s axis tilt of 23.4o from the ecliptic plane.

Materials

Bright light source (not fluorescent)
Balloon
Protractor
Masking tape
2 liquid crystal thermometers
Ruler, yardstick or meter stick
Marker

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Download Student Worksheet & Exercises

For a light source, try lamps with 100W bulbs (without lamp shades). Make sure there’s room to walk all the way around it. You’ll want to circle the lamp at a distance of about 2 feet away.
Mark on the floor with tape and label the four positions: winter, spring, summer, and fall. They should be at the 12, 3, 6, and 9 o’clock positions. Winter is directly across from summer. The Earth rotates counterclockwise around the Sun when viewed from above.
Blow up your balloon so it’s roughly round-shaped (don’t blow it up all the way). Mark and label the north and south poles with your marker. Draw an equator around the middle circumference.
The Earth doesn’t point its north pole straight up as it goes around the Sun. It’s tilted over 23.4o. here’s how you find this point on your balloon:
1. Put the South Pole mark on the table, with north pointing straight up. Find the midway point between the equator and the North Pole and make a tiny mark. This is the 45o latitude point. You’ll need this to find the 23o mark.
2. Find the midway point between the 45o and the North Pole and make another mark, larger this time and label it with 23o. When this mark is pointing up, the Earth is tilted over the right amount.
3. You’ll need to do this three more times so you can draw a line connecting the dots. You want to draw the latitude line at 23o so you can rotate the balloon as you move around to the different seasons. The line will always be pointed up.
Place the thermometers on the balloon at these locations:
1. Find the halfway point between the South Pole and the equator. Put one thermometer on this mark.
2. Put the other thermometer on the northern hemisphere’s 45o mark from above.
Make sure your lamp is facing the balloon as you stand on summer. Let the balloon be heated by the lamp for a couple of minutes and then record the temperature in the data table.
Rotate the lamp to point to fall. Move your balloon to fall, rotating the balloon so that the thermometers are facing the lamp. Wait a few more minutes and take another reading.
Rotate the lamp to point to winter. Move your balloon to winter, rotating the balloon so that the thermometers are facing the lamp. Wait a few more minutes and take another reading.
Rotate the lamp to point to spring. Move your balloon to spring, rotating the balloon so that the thermometers are facing the lamp. Wait a few more minutes and take another reading. You’ve completed a data set for planets with an axis tilt of about 23o, which includes the Earth, Mars, Saturn and Neptune.
Repeat steps 1-9 for Mercury. Note that Mercury does not have an axis tilt, so the North Pole really points straight up. Jupiter (3.1o axis tilt) and Venus (2.7o) are very similar. The Moon’s axis tilt is 6.7o, so you can approximate these four objects with a 0o axis tilt.
Repeat steps 1-9 for Uranus. Since the axis tilt is 97.8o, you can approximate this by pointing the north pole straight at the Sun during summer (90o axis tilt). The orbit for Uranus is 84 years, which means 21 years passes between each season. The north pole will experience continued sunlight for 42 years from spring through fall, then darkness for 42 years.

What’s Going On?

The north and south poles only experience two seasons: winter and summer. During a South Pole winter, the Sun will not rise for several months, and also the Sun does not set for several months in the summer. We go into more detail about how this works in a later lesson entitled: Star Trails and Planet Patterns.

At the equator, there’s a wet season and a dry season due to the tropical rain belt. Since the equator is always oriented at the same position to the Sun, it receives the same amount of sunlight and always feels like summer.

The changing of the seasons is caused by the angle of the Sun. For example, in June during summer solstice, the Sun is high in the sky for longer periods of time, which makes warmer temperatures for the Northern Hemisphere. During the December winter solstice, the Sun spends less time in the sky and is positioned much lower. This makes the winters colder. (Don’t forget that seasons are also affected by oceans and winds, though this is out of the scope of this particular activity.)

Exercises

What is the main reason we have seasons on Earth?
Why are there no sunsets on Uranus for decades?
Are there seasons on Venus?

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Planetary Magnetic Fields

Friday February 8, 2019

You’re going to use a compass to figure out the magnetic lines of force from a magnet by mapping the two different poles and how the lines of force connect the two. A magnetic field must come from a north pole of a magnet and go to a south pole of a magnet (or atoms that have turned to the magnetic field.)

Compasses are influenced by magnetic lines of force. These lines are not necessarily straight. When they bend, the compass needle moves. The Earth has a huge magnetic field. The Earth has a weak magnetic force. The magnetic field comes from the moving electrons in the currents of the Earth’s molten core. The Earth has a north and a south magnetic pole which is different from the geographic North and South Pole.

Materials

Bar magnet
Horseshoe magnet
Circular (disk) magnet
Compass
String
Ruler

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Download Student Worksheet & Exercises

Tie a string around your magnet.
Bring it close to the compass.
Which end is the north end of your magnet? Label it with a pencil right on the magnet.
Flip the magnet around by twisting the string so that the compass flips to the opposite pole. Label the opposite site of the magnet with the appropriate letter (N or S).
Bring a second magnet close to the first one. What happens when you bring two opposite poles together? What if the poles are the same?
Now untie or cut the string for the next part of your lab.
Lay a piece of paper on your desk.
Place the magnet in the middle of the paper and trace the outline.
Draw 12 dots (just like on a clock) all the way around the magnet. These are the locations where you will place your compass, so make sure that they are close enough to the magnet so the magnet influences the compass.
Place your compass on one of the dots and look at the direction the arrow is pointing. Remove the compass and draw that exact arrow direction right over your dot. Do this for all 12 dots.
Draw another ring of dots an inch or two out from the first ring and repeat step 9.
Repeat steps 6-10 with a circular magnet on a new sheet of paper.
Repeat steps 6-10 for the horseshoe magnet on another sheet of paper.

What’s Going On?

Right under your feet, there’s a magnet. Go ahead take a look. Lift up your feet and see what’s under there. Do you see it? It’s huge! In fact, it’s the largest magnet on the Earth. As a matter of fact, it is the Earth! That’s right; the Earth is one huge, gigantic, monolithic magnet! We’re going to use a magnet to substitute for the Earth and plot out the magnetic field lines.

The magnetic pole which was attracted to the Earth’s North Pole was labeled as the Boreal or “north-seeking pole” in the 1200s, which was later shortened to “north pole.” To add to the confusion, geologists call this pole the North Magnetic Pole.

Exercises

How are the lines of force different for the two magnets?
How far out (in inches measured from the magnet) does the magnet affect the compass?
What makes the compass move around?
Do you think the compass’s north–south indicator is flipped, or the Earth’s North Pole where the South Pole is? How do you know?

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Sky in a Jar

Friday February 8, 2019

Have you ever wondered why the sky is blue? Or why the sunset is red? Or what color our sunset would be if we had a blue giant instead of a white star? This lab will answer those questions by showing how light is scattered by the atmosphere.

Particles in the atmosphere determine the color of the planet and the colors we see on its surface. The color of the star also affects the color of the sunset and of the planet.

Materials

Glass jar
Flashlight
Fingernail polish (red, yellow, green, blue)
Clear tape
Water
Dark room
Few drops of milk

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Download Student Worksheet & Exercises

Make your room as dark as possible for this experiment to work.
Make sure your label is removed from the glass jar or you won’t be able to see what’s going on.
Fill the clear glass jar with water.
Add a teaspoon or two of milk (or cornstarch) and swirl.
Shine the flashlight down from the top and look from the side – the water should have a bluish hue. The small milk droplets scatter the light the same way our atmosphere’s dust particles scatter sunlight.
Try shining the light up from the base – where do you need to look in order to see a faint red/pink tint? If not, it’s because you are looking for hues that match our real atmosphere, and the jar just isn’t that big, nor is your flashlight strong enough! Instead, look for a very slight color shift. If you do this experiment after being in the dark for about 10 minutes (letting your eyes adjust to the lack of light), it is easier to see the subtle color changes. Just be careful that you don’t let the brilliant flashlight ruin your newly acquired night-vision, or you’ll have to start the 10 minutes all over again.
If you are still having trouble seeing the color changes, shine your light through the jar and onto an index card on the other side. You should see slight color changes on the white card.
Cover the flashlight lens with clear tape.
Paint on the tape (not the lens) the fingernail polish you need to complete the table.
Repeat steps 7-9 and record your data.

What’s Going On?

Why is the sunset red? The colors you see in the sky depends on how light bounces around. The red/orange colors of sunset and sunrise happen because of the low angle the Sun makes with the atmosphere, skipping the light off dust and dirt (not to mention solid aerosols, soot, and smog). Sunsets are usually more spectacular than sunrises, as more “stuff” floats around at the end of the day (there are less particles present in the mornings). Sometimes just after sunset, a green flash can be seen ejecting from the setting Sun.

The Earth appears blue to the astronauts in space because the shorter, faster wavelengths are reflected off the upper atmosphere. The sunsets appear red because the slower, longer wavelengths bounce off the clouds.Sunsets on other planets are different because they are farther (or closer) to the Sun, and also because they have a different atmosphere than planet Earth. The image shown here is a sunset on Mars. Uranus and Neptune appear blue because the methane in the upper atmosphere reflects the Sun’s light and the methane absorbs the red light, allowing blue to bounce back out.

Exercises

What colors does the sunset go through?
Does the color of the light source matter?

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Magnetic Tornadoes

Friday February 8, 2019

This lab is a physical model of what happens on Mercury when two magnetic fields collide and form magnetic tornadoes.

You’ll get to investigate what an invisible magnetic tornado looks like when it sweeps across Mercury.

Materials

Two clear plastic bottles (2 liter soda bottles work best)
Steel washer with a 3/8 inch hole
Ruler and stopwatch
Glitter or confetti (optional)
Duct tape (optional)

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Download Student Worksheet & Exercises

Determine the different water conditions, such as: changing the temperature, changing the volume (height of water), adding another molecule such as oil, isopropyl alcohol, vinegar, and dish soap, adding solid pieces such as glitter, salt, sugar, or small grains. The different mixtures will give different vortex rotation speeds and different drain times. This is equivalent to changing the atmosphere on Earth and seeing how it affects weather (not magnetic) tornadoes. Write the conditions you wish to test in the data table before you start.
Fill one of the soda bottles with water using the data table. Set the bottle upright on the table.
Set the washer on top of the bottle opening. Make sure there’s no cap on the bottle.
Invert the empty bottle over the water‐filled bottle and line up the openings so they can be easily taped together. You want to tape them before they get wet with the washer between them.
Place the two bottles on a table and watch the water drip from the top to the lower bottle as air bubbles move from bottom to top.
Invert so the water is in the top bottle and circle it a couple of times to start a whirlpool in the bottle. You should see a vortex form inside as the top drains into the lower bottle. The hole in the vortex lets the airfrom the lower bottle flow easily into the upper bottle, so the upper drains easily.
When you’ve finished, empty your bottle and add a different solution and repeat the experiment.

What’s Going On?

Mercury looks peaceful at first glance. However, when you measure the surface with scientific instruments, you’ll see how the Sun blasts away any hope Mercury has of a thin atmosphere with its radiation and solar wind. Not only that, Mercury is ravaged by invisible magnetic tornadoes that start from the planet’s interior magnetic field. If you’ve ever experienced a tornado, you know how terrifying they can be. Now imagine they are the diameter of your entire planet.

These tornadoes are different from the Earth’s, which form when two weather systems smack into each other, creating instability in the atmosphere. The magnetic tornadoes on Mercury form when two magnetic fields collide. These monstrous cyclones form without warning and disappear within minutes.

Magnetic fields, like the Earth’s, are invisible shields that constantly protect us from the Sun. Our Earth is constantly being bombarded with high energy particles that are deflected off the magnetosphere of our planet. Mercury’s magnetic field is weak and it’s constantly being blasted by solar wind, which also carries a magnetic field. When these two fields collide, the magnetic fields spiral and twist to form a magnetic tornado. (Solar wind is a stream of high energy particles from the Sun’s outer atmosphere.)

Exercises

Define an atmosphere.
What is a magnetic field?
Where do magnetic fields come from in planets?
Which planets do not have a magnetic field?

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Build a REAL Scale Model of the Solar System

Friday February 8, 2019

Ever wonder exactly how far away the planets really are? Here’s the reason they usually don’t how the planets and their orbits to scale – they would need a sheet of paper nearly a mile long!

To really get the hang of how big and far away celestial objects really are, find a long stretch of road that you can mark off with chalk. We’ve provided approximate (average) orbital distances and sizes for building your own scale model of the solar system.

When building this model, start by marking off the location of the sun (you can use chalk or place the objects we have suggested below as placeholders for the locations). Are you ready to find out what’s out there? Then let’s get started.

Materials:

measuring tape (the biggest one you have)
tape or chalk to mark off the locations
2 grains of sand or white sugar
12″ beach ball
3 peppercorns
golf or ping pong ball
shooter-size marble
2 regular-size marbles

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Download Student Worksheet & Exercises

All distances are measured from the center of the sun. (In some cases, you might just want to use the odometer in your car to help you measure the distance!

Sun (12″ beach ball) at the starting point.

Mercury (grain of sand) is 41 feet from the sun.

Venus (single peppercorn) is 77 feet from the sun.

Earth (single peppercorn) is 107 feet from the sun.

Mars (half a peppercorn) is 163 feet from the sun.

Jupiter (golf or ping pong ball) is 559 feet from the sun.

Saturn (shooter-size marble) is 1,025 feet from the sun.

Uranus (regular-size marble) is 2,062 feet from the sun.

Neptune (regular marble) is 3,232 feet from the sun.

Pluto (grain of sand) is 4,248 feet from the sun.

Nearest Star (Alpha Centauri) is 5500 miles from the sun.

Is Your Solar System Too Big?

If these distances are too large for you, simply shrink all objects to the size of the period at the end of this sentence and you’ll get your solar system to fit inside your house using these measurements below.

First, draw a tiny dot for the Sun. The diameter of the sun for this scale model is 0.1″, but we’re going to ignore this and all other planet diameters so we can fit this model within a 35′ scale.

We’re going to ignore the sizes of the planets and just focus on how far apart everything is. All distances listed below are measured from the sun. Start by marking off the position of the sun with the tip of a sharp pencil.

Here are the rest of the distances you need to mark off:

Mercury is 4 inches from the sun.

Venus is 7.75 inches from the sun.

Earth is 10 inches from the sun.

Mars is 1′ 4″ from the sun.

Jupiter is 4′ 8″ from the sun.

Saturn is 8′ 6.5″ from the sun.

Uranus is 17′ 2″ from the sun.

Neptune is 26′ 11″ from the sun.

Pluto is 35′ 5″ from the sun.

Our nearest star, Alpha Centauri, is approximately 46 miles from the sun.

Did You Notice…?

Are you mind-boggled yet? Did you notice how the solar system is really just ’empty space’? Our models shown here are too small to start bringing in the moons, but you can see why posters showing the planets are not drawn to scale. What are your thoughts on this experiment? Tell us in the comment area below!

For Advanced Students:

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If you really want to play with the different distances on your own, use this orbital calculator online to help convert the distances for you.

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Solar System Treasure Hunt

Friday February 8, 2019

After you've participated in the Planetarium Star Show, treat your kids to a Solar System Treasure Hunt! You'll need some sort of treasure (I recommend astronomy books or a pair of my favorite binoculars, but you can also use 'Mars' candy bars or home made chocolate chip cookies (call them Galaxy Clusters) instead.

You can print out the clues and hide these around your house on a rainy day. Did you know that I made these clues up myself as a refresher course after the astronomy presentation? Enjoy!

P.S. Do you need help using your binoculars? Click here.

P.P.S. How can you tell if you have a good pair of binoculars? Click here.

P.P.P.S. How do you find meteorites tonight? Click here.

P.P.P.P.S. Want to learn how to use a telescope? Click here.

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Astronomy Clues
Click here to download the PDF version or the Word DOC version.

Download Student Worksheet & Exercises

You can print out images of each planet and match them up with the clues indicated below. Post images of each of the planets along with the clue for the next one to really make this an out-of-this-world experience!

The Sun (CLUE #1): Hand this one to the kids to get started.

This object is hot, but not on fire.
Explore the dryer but don’t perspire!

Mercury (CLUE #2): Hide this clue below in the dryer.

This planet is closest, but not the hottest.
Check the sock drawer, and don’t be modest!

Venus (CLUE #3): Hide this clue below in the sock drawer.

This planet is so hot it can melt a cannonball,
Crush spaceships, rain acid, and is in tree tall.

Earth (CLUE #4): Hide this clue below in a tree (or plant).

Most of this planet is covered with water.
Visit the bathtub without making it hotter.

Mars (CLUE #5): Hide this clue below in the bathtub.

This planet is basically a rusty burp.
Discover the refrigerator and take a slurp.

Jupiter (CLUE #6): Hide this clue below next to the milk.

A planet so large it can hold the rest,
Explore our library with infinite zest!

Saturn (CLUE #7): Hide this clue below with a stack of books.

This planet had rings, but not made of gold.
Explore near the front door like an astronaut bold!

Uranus (CLUE #8): Hide this clue below on the front door.

Smacked so hard it now rolls on its side,
Find the window that is ever so wide.

Neptune (CLUE #9): Hide this clue below by sticking it on a window.

Check the sink for hurricane,
gigantic blue farts, and diamond rain.

Pluto (CLUE #10): Hide this clue below near the sink with the TREASURE!

Instead of one there were two, then four…
Visit the mailbox for the one that is no more.

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Force-full Cereal

Friday February 8, 2019

Did you know that your cereal may be magnetic? Depending on the brand of cereal you enjoy in the morning, you’ll be able to see the magnetic effects right in your bowl. You don’t have to eat this experiment when you’re done, but you may if you want to (this is one of the ONLY times I’m going to allow you do eat what you experiment with!) For a variation, pull out all the different boxes of cereal in your cupboard and see which has the greatest magnetic attraction.

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Materials:

a bowl of cereal with milk
spoon

Download Student Worksheet & Exercises

Fill the bowl with milk.
Put about 20 pieces of cereal (not the whole box!) into the bowl.
Stir up the bowl a little and watch what happens.

If you watched carefully, you saw that as the cereal “O’s” got close to one another, they attracted each other. The closer they got, the stronger was their attraction to each other and the faster they moved towards each other. If you wait and watch long enough, you get a nice tight batch of cereal all clustered together in one or two big blobs. This activity is a great illustration of what is meant by the inverse square law because the attraction between “O’s” was stronger the closer they got to each other.

I discovered this activity one morning as I was eating cereal. The same thing happens with bubbles when you’re doing the dishes. Science is everywhere! Feel free to eat the cereal!

Exercises

Why do the pieces of cereal stick to each other?
Does the cereal move slower or faster the closer the pieces come in contact with each other?
What other cereals does it work for?

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Special Science Teleclass: Magnetism

Friday February 8, 2019

This is a recording of a recent live teleclass I did with thousands of kids from all over the world. I’ve included it here so you can participate and learn, too!

Discover how to detect magnetic fields, learn about the Earth’s 8 magnetic poles, and uncover the mysterious link between electricity and magnetism that marks one of the biggest discoveries of all science…ever.

Materials:

Box of paperclips
Two magnets (make sure one of them ceramic because we’re going to break it)
Compass
Hammer
Nail
Sandpaper or nail file
D cell battery
Rubber band
Magnet Wire

Optional Materials if you want to make the Magnetic Rocket Ball Launcher:Four ½” (12mm) neodymium magnets

Nine ½” (12 mm) ball bearings
Toilet paper tube or paper towel tube
Ruler with groove down the middle
Eight strong rubber bands
Scissors

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Key Concepts

While the kids are playing with the experiments see if you can get them to notice these important ideas. When they can explain these concepts back to you (in their own words or with demonstrations), you’ll know that they’ve mastered the lesson.

Magnets

Magnetic fields are created by electrons moving in the same direction. Electrons can have a “left” or “right” spin. If an atom has more electrons spinning in one direction than in the other, that atom has a magnetic field.
If an object is filled with atoms that have an abundance of electrons spinning in the same direction, and if those atoms are lined up in the same direction, that object will have a magnetic force.
A field is an area around an electrical, magnetic or gravitational source that will create a force on another electrical, magnetic or gravitational source that comes within the reach of the field.
In fields, the closer something gets to the source of the field, the stronger the force of the field gets. This is called the inverse square law.
A magnetic field must come from a north pole of a magnet and go to a south pole of a magnet (or atoms that have turned to the magnetic field.)
All magnets have two poles. Magnets are called dipolar which means they have two poles. The two poles of a magnet are called north and south poles. The magnetic field comes from a north pole and goes to a south pole. Opposite poles will attract one another. Like poles will repel one another.
Iron and a few other types of atoms will turn to align themselves with the magnetic field. Over time iron atoms will align themselves with the force of the magnetic field.
The Earth has a huge magnetic field. The Earth has a weak magnetic force. The magnetic field comes from the moving electrons in the currents of the Earth’s molten core. The Earth has a north and a south magnetic pole which is different from the geographic north and south pole.
Compasses turn with the force of the magnetic field.

Electromagnetism

Electricity is moving electrons. Magnetism is caused by moving electrons. Electricity causes magnetism.
Magnetic fields can cause electricity.

What’s Going On?

The scientific principles we’re going to cover were first discovered by a host of scientists in the 19^th century, each working on the ideas from each other, most prominently James Maxwell. This is one of the most exciting areas of science, because it includes one of the most important scientific discoveries of all time: how electricity and magnetism are connected. Before this discovery, people thought of electricity and magnetism as two separate things. When scientists realized that not only were they linked together, but that one causes the other, that’s when the field of physics really took off.

Questions

When you’ve worked through most of the experiments ask your kids these questions and see how they do:

How many poles do magnets have, and what are they?
What happens when you bring two like poles together?
How do I know which pole is which on a magnet?
Is the magnetic force stronger or weaker the closer a magnet gets to another magnet?
What kinds of materials are magnets made from?
Name three objects that stick to a magnet.
Name three that don’t stick to a magnet.
What does a compass detect? How do you know when it’s detected it?

Answers:

How many poles do magnets have, and what are they? Two. North and South poles.
What happens when you bring two like poles together? They repel each other.
How do I know which pole is which on a magnet? Put two magnets together and find the spot where they are repelling the strongest. The poles facing each other are the same. Or bring it close to a compass. If the magnet attracts the needle to north, then the magnet’s pole is the south pole.
Is the magnetic force stronger or weaker the closer a magnet gets to another magnet? Stronger.
What kinds of materials are magnets made from? Iron, nickel and cobalt.
Name three objects that stick to a magnet. Paperclips, pipe cleaners, and staples.
Name three that don’t stick to a magnet. US quarter, glass, plastic.
What does a compass detect? How do you know when it’s detected it? The direction of a magnetic field. When the needle is deflected, the compass is in a magnetic field.

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Force-full Cereal

Friday February 8, 2019

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Materials:

a bowl of cereal with milk
spoon

Download Student Worksheet & Exercises

Fill the bowl with milk.
Put about 20 pieces of cereal (not the whole box!) into the bowl.
Stir up the bowl a little and watch what happens.

I discovered this activity one morning as I was eating cereal. The same thing happens with bubbles when you’re doing the dishes. Science is everywhere! Feel free to eat the cereal!

Exercises

Why do the pieces of cereal stick to each other?
Does the cereal move slower or faster the closer the pieces come in contact with each other?
What other cereals does it work for?

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Flying Paper Clip

Friday February 8, 2019

Have you ever been close to something that smells bad? Have you noticed that the farther you get from that something, the less it smells, and the closer you get, the more it smells? Well forces sort of work in the same way.

Forces behave according to a fancy law called the inverse-square law. To be technical, an inverse-square law is any physical law stating that some physical quantity or strength is inversely proportional to the square of the distance from the source of that physical quantity.

The inverse-square law applies to quite a few phenomena in physics. When it comes to forces, it basically means that the closer an object comes to the source of a force, the stronger that force will be on that object. The farther that same object gets from the force’s source, the weaker the effect of the force.

Mathematically we can say that doubling the distance between the object and the source of the force makes the force 1/4th as strong. Tripling the distance makes the force 1/9th as strong. Let’s play with this idea a bit.

Here’s what you need:

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magnet
paper clip
string
tape

Using a magnet (the stronger the better), paper clip, string (or yarn or even dental floss!), and tape, you can make a flying paper clip.

OPTIONAL: If you happen to have a spring scale and ruler, get those out, too…otherwise, just skip these items – they are not essential to understanding the concept here.

Download Student Worksheet & Exercises

1. Tie about 4 inches of string to a paper clip.
2. Tape the magnet to the table.
3. Hold the end of the string that is not tied to the paper clip and let the paper clip dangle.
4. Slowly bring the paper clip closer and closer to the magnet.
5. Notice that the closer you get to the magnet, the stronger the force of the magnetic field is on the paper clip.

If you have a spring scale:
6. Attach the paper clip to the spring scale.
7. Move the paper clip closer to the magnet until the magnetic field affects the paper clip.
8. Measure how far the paper clip is from the magnet with a ruler.
9. Measure how much pull there is on the paper clip. Use newtons if your spring scale shows that measurement, but grams are OK if it doesn’t.
10. Bring the paper clip a half inch closer and measure the force of the pull again either in grams or Newtons.
11. Continue to get closer to the magnet half an inch at a time, measuring the force until you can’t get any closer.

What you may have noticed here was that the closer you got the paper clip to the magnet (the object causing the force field) the stronger the force was on the paper clip. You have just seen the inverse-square law in action!

Exercises:

Circle one: The closer you get to the magnet, the (stronger | weaker) the force of the magnetic field is on the paper clip.
Why does it matter which way you orient the magnet in this experiment?
Which magnet has the strongest magnetic field?
Is the north or south pole stronger on a magnet?

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Detecting the Magnetic Field

Friday February 8, 2019

Remember, there are four different kinds of forces: strong nuclear force,
electromagnetism, weak nuclear force, and gravity. There are also four basic force fields that you come into contact with all the time. They are the gravitational field, the electric field, the magnetic field, and the electromagnetic field. Notice that those four force fields really only use two of the four different kinds of force: electromagnetism and gravity. Let’s take a quick look at what causes these four fields and what kind of objects they can affect, starting with the magnetic field.

Here’s what you need:
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you
a compass

You’re probably fairly familiar with magnetic fields. If you’ve ever stuck a magnet to a refrigerator, you’ve taken advantage of magnetic fields. Sticking a magnet to a refrigerator is one of those every day experiences that should just be absolutely flabbergasting. There you are holding an “I’d Rather be Relative” magnet and it sticks to the fridge! But wait a minute, if you put it on the wall… it falls off! How does it “know” what to stick to? Not only does it stick to the fridge, it also pushes some things away, attracts other things and couldn’t care less about still other things. What’s that all about?! We rarely think about what magnets do but, wow, the things they do are weird!

Magnetic fields come from objects that have a surplus of electrons all moving in the same direction. This can be an electric wire with current running through it or one of several special types of metals. Iron, nickel and cobalt are the most common metals that can be magnetic. Magnetic fields can only affect objects that can be magnetic themselves. That’s why a magnet can attract an iron nail, but it can’t attract an aluminum can. The iron nail can be magnetic, but the aluminum cannot. Magnets can also be attractive or repulsive. Two magnets with the same kind of poles facing one another will push themselves apart. Two magnets with opposite poles facing one another will pull themselves together.

Download Student Worksheet & Exercises

Using a compass and the Earth, you can do a simple experiment to detect the magnetic field of our planet. (If you don’t have a compass, just slide a magnet along the length of a needle several times (make sure you only swipe in one direction!) then stick it through a cork or bit of foam. Float the needle-foam thing in a cup of water.)

1. Look at the compass

2. Walk anywhere and keep your eye on the compass.

3. Turn around in circles and keep your eye on the compass (don’t get too dizzy).

Again a very simple little activity, but I hope you can see the point. No matter where you went or what you did, that needle always pointed the same direction! The Earth’s magnetic force field, another strange and mysterious force, always pushes that needle in the same direction. It’s invisible and you can’t feel it…but the needle can!

Exercises

Why does the needle need the foam?
Why do we use water?
What are the forces in a magnetic field?

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Rocket Ball Launcher

Friday February 8, 2019

This is a satisfyingly simple activity with surprising results. Take a tennis ball and place it on top of a basketball… then release both at the same time.

Instant ball launcher!

You’ll find the top ball rockets off skyward while the lower ball hit the floor flat (without bouncing much, if at all). Now why is that? It’s easier to explain than you think…

Remember momentum? Momentum can be defined as inertia in motion. Something must be moving to have momentum. Momentum is how hard it is to get something to stop or to change directions. A moving train has a whole lot of momentum. A moving ping pong ball does not. You can easily stop a ping pong ball, even at high speeds. It is difficult, however, to stop a train even at low speeds.

Mathematically, momentum is mass times velocity, or Momentum=mv.

One of the basic laws of the universe is the conservation of momentum. When objects smack into each other, the momentum that both objects have after the collision, is equal to the amount of momentum the objects had before the crash. Once the two balls hit the ground, all the larger ball’s momentum transferred to the smaller ball (plus the smaller ball had its own momentum, too!) and thus the smaller ball goes zooming to the sky.

Materials:

two balls, one significantly larger than the other

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Download Student Worksheet & Exercises

Do you see how using a massive object as the lower ball works to your advantage here? What if you shrink the smaller ball even more, to say bouncy-ball size? Momentum is mass times by velocity, and since you aren’t going to change the velocity much (unless you try this from the roof, which has its own issues), it’s the mass that you can really play around with to get the biggest change in your results. So for momentum to be conserved, after impact, the top ball had to have a much greater velocity to compensate for the lower ball ‘s velocity going to zero.

You can also try a small bouncy ball (about the size of a quarter) and a larger bouncy ball (tennis-ball size) and rest the small one on top of the large one. Hold upright as high as you can, then release. If the balls stay put (the small one stays on top of the larger) at impact, the energy transfer will create a SUPER high bounce for the small ball. (Note how high the larger ball bounces when dropped.)

What happens if you try THREE?

Forever Falling

Friday February 8, 2019

If I toss a ball horizontally at the exact same instant that I drop another one from my other hand, which one reaches the ground first? For this experiment, you need: [am4show have=’p8;p9;p11;p38;p72;p92;’ guest_error=’Guest error message’ user_error=’User error message’ ]

2 rulers or paint sticks. Any thing wide and flat
2 coins or poker chips
A sharp eye and ear
A partner is good for this one too

Download Student Worksheet & Exercises
1. Place one of the rulers flat so that it is diagonal across the edge of a table with half the ruler on the table and half sticking off.

2. Place one coin on the table, just in front of the ruler and just behind the edge of the table. Place the other coin on the ruler on the side where it’s off the table.

3. Put your finger right in the middle of the ruler on the table so that you are holding it in such a way that it can spin a bit under your finger. Now with the other ruler you are going to smack the end of the first ruler so that the first ruler pushes the coin off the desk and the coin that’s resting on the ruler falls to the ground.

4. Now, before you smack the ruler, make a prediction. Will the coin that falls straight down or the coin that is flying forward hit the ground first?

5. Try it. Do the test and look and listen carefully to what happens. It’s almost better to use your ears here than your eyes. Do it a couple of times.

Are you surprised by what you see and/or hear? Most people are. It’s not what you would expect.

The coins hit the ground at the SAME time. Is that odd or what?

Did you read the first sentence at the top of this lab? What do you think will happen?

The balls will hit the ground at the exact SAME time.

Gravity doesn’t care if something is moving horizontally or not. Everything falls toward the center of the Earth at the same rate.

Let me give you a better example: A bullet fired parallel to the ground from a gun and a bullet dropped from the same height at the same time will both hit the ground at the same time. Even though the one fired lands a mile away! It seems incredible, but it’s true.

Gravity doesn’t care what size something is or whether or not it is moving, Gravity treats all things equally and accelerates them the same.

Notice, that I say gravity accelerates all things equally, not gravity pulls on all things equally. Gravity does pull harder on some things than on other things. This is why I weigh more than a dog. I am made of more stuff (I have more atoms) than the average dog, so gravity pulls on me more.

Weight is nothing more than a measure of how much gravity is pulling on you. This is why you can be “weightless” on a scale in space. You are still made of stuff, but there’s a balance of the gravity that is pulling on you and the outward force due to the acceleration since you’re moving in a circle (which you do in order to remain in orbit), so it feels like you have no weight.

The larger a body is, the more gravitational pull or the larger a gravitational field it will have.

The Moon has a fairly small gravitational field (if you weighed 100 pounds on Earth, you’d only be 17 pounds on the Moon), the Earth’s field is fairly large and the Sun has a HUGE gravitational field (if you weighed 100 pounds on Earth, you’d weigh 2,500 pounds on the sun!).

As a matter of fact, both the dog and I both have gravitational fields! Since we are both bodies of mass we have a gravitational field which will pull things towards us. All bodies have a gravitational field. However, my mass is sooooo small that the gravitational field I have is miniscule. Something has to be very massive before it has a gravitational field that noticeably attracts another body.

So what’s the measurement for how much stuff you’re made of? Mass. Mass is basically a weightless measure of how much matter makes you, you. A hamster is made of a fairly small amount of stuff so she has a small mass. I am made of more stuff, so my mass is greater than the hamster’s. Your house is made of even more stuff so its mass is greater still.

So, here’s a question. If you are “weightless” in space, do you still have mass? Yes, the amount of stuff you’re made of is the same on Earth as it is in your space ship. Mass does not change but since weight is a measure for how much gravity is pulling on you, weight will change.

Did you notice that I put weightless in quotation marks? Wonder why?

Weightlessness is a myth! Believe it or not, one is never weightless. A person can be pretty close to weightless in very deep space but the astronauts in a space ship actually do have a bit of weight.

Think about it for a second. If a space ship is orbiting the Earth what is it doing? It’s constantly falling! If it wasn’t moving forward at 10’s of thousands of miles an hour it would hit the Earth. It’s moving fast enough to fall around the curvature of the Earth as it falls but, indeed, it’s falling as the Earth’s gravity is pulling it to us.

Otherwise the ship would float out to space. So what is the astronaut doing? She’s falling too! The astronaut and the space ship are both falling to the Earth at the same rate of speed and so the astronaut feels weightless in space. If you were in an elevator and the cable snapped, you and the elevator would fall to the Earth at the same rate of speed. You’d feel weightless! (Don’t try this at home!)

Exercises

True or false? Gravity pulls on all things equally.
True or false? Gravity accelerates all things equally.
In your own words, why do the coins hit the ground at the same time? Is this what you’d expect to happen on Mars?

The rest of this experiment is for advanced students…[/am4show]

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For advanced students:

Either now, or at some point in the future you may ask yourself this question, “How can gravity pull harder (put more force on some things, like bowling balls) and yet accelerate all things equally?” When we get into Newton’s laws in a few lessons you’ll realize that doesn’t make any sense at all. More force equals more acceleration is basically Newton’s Second law.

Now, lets get back to gravity and acceleration. Let’s take a look at a bowling ball and a golf ball. Gravity puts more force on the bowling ball than on the golf ball. Soooo the bowling ball should accelerate faster since there’s more force on it. However, the bowling ball is heavier soooo it is harder to get it moving. Vice versa, the golf ball has less force pulling on it but it’s easier to get moving. Do you see it? The force and inertia thing equal out so that all things accelerate due to gravity at the same rate of speed!

Gravity had to be one of the first scientific discoveries. Whoever the first guy was to drop a rock on his foot, probably realized that things fall down! However, even though we have known about gravity for many many years, it still remains one of the most elusive mysteries of science. At this point, nobody knows what makes things move towards a body of mass.

Why did the rock drop towards the Earth and on that guy’s foot? We still don’t know. We know that it does, but we don’t know what causes a gravitational attraction between objects. Gravity is also a very weak force. Compared to magnetic forces and electrostatic forces, the gravitational force is extremely weak. How come? No one knows. A large amount of amazing brain power is being used to discover these mysteries of gravity. Maybe it will be you who figures this out!

Advanced students: Download your Forever Falling Lab here.

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A Weighty Issue

Friday February 8, 2019

This lesson may give you a sinking sensation but don’t worry about it. It’s only because we’re talking about gravity. You can’t go anywhere without gravity. Even though we deal with gravity on a constant basis, there are several misconceptions about it. Let’s get to an experiment right away and I’ll show you what I mean.

If I drop a ping pong ball and a golf ball from the same height, which one hits the ground first? How about a bowling ball and a marble?

Here’s what you need:

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ping pong ball
golf ball
you

Download Student Worksheet & Exercises

For this experiment, you’ll need:

Two objects of different weights. A marble and a golf ball, or a tennis ball and a penny for example.
A sharp eye
A partner

1. Take a careful look at both objects and make a prediction about which object will hit the ground first if they are dropped from the same height.

2. Test your prediction. Hold both objects at the same height. Make sure the bottom of both objects are the same distance from the floor.

3. Let them go as close to the same time as possible. Sometimes it’s helpful to roll them off a book.

4. Watch carefully. Which hits the ground first, the heavier one or the lighter one? Try it a couple of times and watch carefully. It will be a little easier for the person who isn’t dropping them to see what happens.

What you should see is that both objects hit the ground at the same time! Gravity accelerates both items equally and they hit the ground at the same time. Any two objects will do this, a brick and a Buick, a flower and a fish, a kumquat and a cow!

“But,” I hear you saying, “if I drop a feather and a flounder, the flounder will hit first every time!” Ok, you got me there. There is one thing that will change the results and that is air resistance.

The bigger, lighter and fluffier something is, the more air resistance can effect it and so it will fall more slowly. Air resistance is a type of friction which we will be talking about later. In fact, if you removed air resistance, a feather and a flounder would hit the ground at the same time!!!

Where can you remove air resistance? The moon!!! One of the Apollo missions actually did this (well, they didn’t use a flounder they used a hammer). An astronaut dropped a feather and a hammer at the same time and indeed, both fell at the same rate of speed and hit the surface of the moon at the same time.

Ask someone this question: Which will hit the ground first, if dropped from the same height, a bowling ball or a tennis ball? Most will say the bowling ball. In fact, if you asked yourself that question 5 minutes ago, would you have gotten it right? It’s conventional wisdom to think that the heavier object falls faster. Unfortunately, conventional wisdom isn’t always right. Gravity accelerates all things equally. In other words, gravity makes all things speed up or slow down at the same rate. We will be discussing acceleration more in a later lesson. If you would like more details on the math of this, it will be at the end of this lesson in the Deeper Lesson section.

This photo shows a statue of Aristotle, a famous Greek philosopher who contributed many ideas to science.

This is a great example of why the scientific method is such a cool thing. Many, many years ago, there was a man of great knowledge and wisdom named Aristotle. Whatever he said, most people believed to be true. The trouble was he didn’t test everything that he said. One of his statements was that objects with greater weight fall faster than objects with less weight. Everyone believed that this was true.

Hundreds of years later Galileo came along and said “Ya know…that doesn’t seem to work that way. I’m going to test it” The story goes that Galileo grabbed a melon and an orange and went to the top of the Leaning Tower of Pisa. He said, “Look out below!” and dropped them! By doing that, he showed that objects fall at the same rate of speed no matter what their size.

It is true that it was Galileo who “proved” that gravity accelerates all things equally no matter what their weight, but there is no real evidence that he actually used the Leaning Tower of Pisa to do it.

Advanced Students: Download your Gravity Lab here.

Exercises

What did you notice from your data? Did heavier or lighter objects fall faster? Did more massive objects or smaller objects fall faster? What characteristic seemed to matter the most?
Is gravity a two-way force, like the attractive-repulsive forces of a magnet?
If I were to drop a bowling ball and a balloon filled with a gas six times heavier than air (sulfur hexafluoride SF₆) and inflated to the exact size of the bowling ball from my roof, which will strike the ground first?

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Building Bridges

Friday February 8, 2019

What keeps building from toppling over in the wind? Why are some earthquake-proof and others not? We’re going to look at how engineers design buildings and bridges while making our own.

Here’s what you need:
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Index cards
Blocks
Straws
Clay
Disposable cups

Watch the video:

Download Student Worksheet Exercises

Exercises

What are three different kinds of forces?
Using only blocks, what kind of wall design is the weakest?
Why does the bridge seem stronger when a card is arched underneath?

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Barrel Roof

Friday February 8, 2019

This roof can support over 400 times its own weight, and you don’t need tape! One of the great things about net forces is that although the objects can be under tremendous force, nothing moves! For every push, there’s an equal and opposite pull (or set of pulls) that cancel each other out.

This barrel roof is an excellent example of how to the forces all cancel out and the roof stands strong (hopefully!) If you have trouble with this experiment, just use cardstock or other heavy weight paper instead of regular copy paper.

Here’s what you need:
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Print out this template.
Scissors
2 pencils
Thread
Flat book or light clipboard
Extra paper to load the roof

Watch the video:

Download Student Worksheet & Exercises

Exercises

What is Newton’s Third Law?
What kind of groups do forces come in?
What is another name for Newton’s Third Law?

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Newton’s Third Law of Motion

Friday February 8, 2019

Third Law of Motion: For every action, there is an equal and opposite reaction.

Force is a push or a pull, like pulling a wagon or pushing a car. Gravity is a force that attracts things to one another. Weight is a measure of how much gravity is pulling on an object.

Gravity accelerates all things equally. Which means all things speed up (accelerate) the same amount as they fall. Acceleration is the rate of change in velocity. In other words, how fast is a change in speed and/or a change in direction happening.

Materials: balloon
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Hold a balloon between your fingers and let go. Which way does the air inside the balloon travel relative to the balloon itself?

Answer: The balloon travels to the right and the air inside the balloon (at least initially) travels to the left.

Find out more about this key principle in Unit 1 and Unit 2.

Download Student Worksheet & Exercises

Exercises

What is Newton’s Third Law?
Give three examples of forces in pairs.
A rope is attached to a wall. You pick up the rope and pull with all you’ve got. A scientist walks by and adds a force meter to the rope and measures you’re pulling with 50 Newtons. How much force does the wall experience?
Can rockets travel in space if there’s nothing to push off of? Explain your answer.

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Newton’s Second Law of Motion

Friday February 8, 2019

Second Law of Motion: Momentum is conserved. Momentum can be defined as mass in motion. Something must be moving to have momentum. Momentum is how hard it is to get something to stop or to change directions. A moving train has a whole lot of momentum. A moving ping pong ball does not. You can easily stop a ping pong ball, even at high speeds. It is difficult, however, to stop a train even at low speeds.

Materials: garden hose connected to a water faucet

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Place your thumb partway over the end of a garden hose. The water shoots out faster because the same amount of “stuff” has to pass through the exit. When the exit area decreases, less mass can pass through at one time, so the velocity increases.

Mathematically, momentum is mass times velocity, or Momentum=mv.

One of the basic laws of the universe is the conservation of momentum. When objects smack into each other, the momentum that both objects have after the collision, is equal to the amount of momentum the objects had before the crash.

The next video shows you how once the two balls hit the ground, all the larger ball’s momentum transferred to the smaller ball (plus the smaller ball had its own momentum, too!) and thus the smaller ball goes zooming to the sky.

Download Student Worksheet & Exercises

Find out more about this key principle in Unit 1 and Unit 2.

Advanced students: Download your Momentum lab here.

Exercises

What concept does Newton’s Second Law of Motion deal with?
What is momentum?

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Newton’s First Law of Motion

Friday February 8, 2019

First Law of Motion: Objects in motion tend to stay in motion unless acted upon by an external force. Force is a push or a pull, like pulling a wagon or pushing a car. Gravity is a force that attracts things to one another. Gravity accelerates all things equally. Which means all things speed up the same amount as they fall.

Materials: ball
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What happens when you kick a soccer ball? The ‘kick’ is your external force. The ball will continue in a straight line as long as it can, until air drag, rolling resistance, and gravity cause it to stop.

Find out more about this key principle in Unit 1 and Unit 2.

Download Student Worksheet & Exercises

Exercises

What is inertia?
What is Newton’s First Law?
Will a lighter or heavier race car with the same engine win a short-distance race (like the quarter-mile)?

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Detecting the Electric Field

Friday February 8, 2019

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An electric field exists when at least one body is electrically charged. Atoms are filled with positively charged protons and negatively charged electrons. If an object has more electrons than protons, it will be negatively charged and if it has fewer electrons than protons, it will be positively charged. Electric fields, like magnetic fields, can attract and repel. If two bodies have the same kind of charge, that is either both are negative or both are positive, they will push themselves away from each other. If one body has a positive charge and the other has a negative charge, they will attract each other. Charged bodies can also attract bodies that are neither positive nor negative but are just neutral.

Here’s a simple experiment you can do that only needs four simple items:
– head of hair
– balloon
– yardstick or meterstick
– large spoon

Here’s what you do:

Download Student Worksheet & Exercises

Make sure you’ve tried out these Static Electricity experiments and learn how to light a bulb without plugging it into the wall!

Exercises

What happens if you rub the balloon on other things, like a wool sweater?
If you position other people with charged balloons around the table, can you keep the yardstick going?
Can we see electrons?
How do you get rid of extra electrons?
Does the shape of the balloon matter?
Does hair color matter?
Rub a balloon on your head, and then lift it up about 6”. Why is the hair attracted to the balloon?
Why does the hair continue to stand on end after the balloon is taken away?
What other things does the balloon stick to besides the wall?
Why do you think the yardstick moved?
What other things are attracted or repelled the same way by the balloon? (Hint: try a ping pong ball.)

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Look Out Below!

Friday February 8, 2019

If you jump out of an airplane, how fast would you fall? What’s the greatest speed you would reach? Let’s practice figuring it out without jumping out of a plane.

This experiment will help you get the concept of velocity by allowing you to measure the rate of fall of several objects. It’s also a great experiment to record in your science journal.

First, you’ll need to find your materials:

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stop watch
feathers (or small pieces of paper, plastic bag or anything light and fluffy)
a tape measure
If you’re crunching numbers, you’ll also need a calculator.

Now here’s how to do the experiment:

1. Get 5 or so different light and fluffy objects. Feathers of different size, small strips of paper, parts of a plastic bag, cotton balls, whatever is handy.

2. Make a prediction by writing down the objects you chose in order of how fast you think they will fall. The fastest on top, the slowest on the bottom. Leave space to the right of your prediction so that you can write in your conclusions and then compare the two.

3. Make a table with two columns. Use one column to fill in the name of the items. Use the second column to write down the time it took each object to fall.

4. Drop the different items and time them from the moment you let go to the moment they hit the ground. Be sure to drop each item from about the same height. The higher the better. Just be sure not to fall off anything! We don’t want to measure your velocity!! You might want to drop them two or three times to get an average time.

5. Now compare the items. Which one fell the least amount of time (dropped the fastest)? Which one fell the most amount of time (dropped the slowest)? Write your results next to your hypothesis. By the way, did you find anything that dropped slower than a feather? I have seen very few things that take longer to fall straight down than a feather.

Download Student Worksheet & Exercises

Did you see how many of your objects stopped accelerating very quickly? In other words, they reached their terminal velocity soon after you let them go and they fell all the way to the ground at that same constant velocity. This is why a parachute is a sky-diver’s best friend! A human has a decent amount of air resistance but he or she can reach a lethal dose of velocity (120 mph) if dropped from a great height. The parachute increases the air resistance so that the terminal velocity of that sky-diver is quite a bit safer!

Exercises

What is velocity?
How do acceleration and deceleration relate to velocity?
How do we know when an object has reached terminal velocity?

Taking it Further for advanced students:

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We can do a little math here and figure out the actual velocity of your objects. Here’s how to do it:

Measure the height from which you dropped each object. Now take the height of the drop and divide that by the number of seconds it took for it to drop that distance. That’s the velocity of that object. For example, My “from-under-the-couch-six-month-old-dust-bunny” took 3 seconds to fall 6 feet. I take 6 feet and divide it by 3 seconds to get 2 feet/second.

The velocity of my dust bunny is 2 feet/second downward.

Remember, that velocity has a directional component as well as a number. Add a little more math, and I can predict how long my dust bunny will take to fall 15 feet. Take the distance (15 feet) and divide it by the velocity (2 feet/second) and I get 7.5 seconds. It will take my dust bunny 7.5 seconds to fall 15 feet. Hmmm, maybe we should call it a dust snail.

Have you noticed something here? In this experiment, we used a different formula to find out how far something would fall over a given time.

What’s going on? In Unit 1, we ignored their terminal velocity. Those things were in free fall and accelerating (gaining velocity) all the way to the ground. They were never going the same velocity for the entire trip. So, we needed to use the gravitational constant 32 ft/s² in the equation d=1/2 gt² to determine how far something fell in a given amount of time.

For this unit, we are dealing with things that are at an almost constant velocity, (since they reach their terminal velocity quickly) so we can use the much simpler equation d=vt (d is distance, v is velocity and t is time). In the problems we’ve done in this lesson plan, we have modified that formula to find how long the fall took so we’ve used t=d/v.

If you’d like to solve for v you would use v=d/t. Isn’t algebra fun?

Advanced students: Download your terminal velocity lab here.

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Balloon Racers

Friday February 8, 2019

We’re going to experiment with Newton’s Third law by blowing up balloons and letting them rocket, race, and zoom all over the place. When you first blow up a balloon, you’re pressurizing the inside of the balloon by adding more air (from your lungs) into the balloon. Because the balloon is made of stretchy rubber (like a rubber band), the balloon wants to snap back into the smallest shape possible as soon as it gets the chance (which usually happens when the air escapes through the nozzle area). And you know what happens next – the air inside the balloon flows in one direction while the balloon zips off in the other.

Question: why does the balloon race all over the room? The answer is because of something called ‘thrust vectoring’, which means you can change the course of the balloon by angling the nozzle around. Think of the kick you’d feel if you tried to angle around a fire hose operating at full blast. That kick is what propels balloons and fighter aircraft into their aerobatic tricks.

We’re going to perform several experiments here, each time watching what’s happening so you get the feel for the Third Law. You will need to find:

balloons
string
wood skewer
two straws
four caps (like the tops of milk jugs, film canisters, or anything else round and plastic about the size of a quarter)
wooden clothespin
a piece of stiff cardboard (or four popsicle sticks)
hot glue gun

First, let’s experiment with the balloon. Here’s what you can do:

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1. Blow up the balloon (don’t tie it)

2. Let it go.

3. Wheeeee!

4. Tie one end of the string to a chair.

5. Blow up the balloon (don’t tie it).

6. Tape a straw to it so that one end of the straw is at the front of the balloon and the other is at the nozzle of the balloon.

7. Thread the string through the straw and pull the string tight across your room.

8. Let go. With a little bit of work (unless you got it the first time) you should be able to get the balloon to shoot about ten feet along the string.

This is a great demonstration of Newton’s Third Law – the air inside the balloon shoots one direction, and the balloon rockets in the opposite direction. It’s also a good opportunity to bring up some science history. Many folks used to believe that it would be impossible for something to go to the moon because once something got into space there would be no air for the rocket engine to push against and so the rocket could not “push” itself forward.

In other words, those folks would have said that a balloon shoots along the string because the air coming out of the balloon pushes against the air in the room. The balloon gets pushed forward. You now know that that’s silly! What makes the balloon move forward is the mere action of the air moving backward. Every action has an equal and opposite reaction.

Multi-Stage Balloon Rocket

You can create a multi-stage balloon rocket by adding a second balloon to the first just like you see here in the video:

Tie a length of string through the room, having at least twenty feet of clear length. Thread two straws onto the string before securing the end. Punch the bottoms out of two foam coffee cups and tape parallel to the threaded straws.

Blow up balloons while they are inside the cups, so they extend out either end. When blowing up the second balloon, sandwich the untied end of the first inflated balloon between the second inflated balloon surface and inside the cup. Hold the second balloon’s end with a clothespin and release!

Balloon Racecar

Now let’s use this information to create a balloon-powered racecar. You’ll need the rest of the items outlined above to build your racecar. NOTE: in the video, we’re using the popsicle sticks, but you can easily substitute in a sheet of stiff cardboard for the popsicle sticks. (Either one works great!)

Download Student Worksheet & Exercises

You now have a great grasp of Newton’s three laws and with it you understand a good deal about the way matter moves about on Earth and in space. Take a look around. Everything that moves or is moved follows Newton’s Laws.

In the next unit, we will get into Newton’s Third Law a little deeper when we discuss momentum and conservation of momentum by whacking things together *HARD*. But more on this later…

Exercises

What is Newton’s Third Law of Motion?
Why does the balloon stop along the string?

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Advanced students: Download your Balloon Racer Lab here.

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Special Science Teleclass: Rocketry & Spaceflight

Friday February 8, 2019

This is a recording of a recent live teleclass I did with thousands of kids from all over the world. I’ve included it here so you can participate and learn, too!

Blast your imagination with this super-popular class on rocketry! Kids learn about fin design, hybrid and solid-state rocketry, and how rockets make it into space without falling out of orbit. This class is taught by a real live rocket scientist (me!). We’ll launch rockets during the class, too!

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Materials:

straw
paperclip
rubber band
index card
popsicle stick
scissors
masking tape
water
alka-seltzer tablets (generic brands work fine)
film canister or small container with tight-fitting lid
OPTIONAL: Small toy car

Download your student worksheet here.

Below you will find an older version of the same teleclass. We are making a different experiment during class, so the materials you will need are a little different:

Materials:

2L soda bottle
1/2″ PVC pipe
duct tape
pen or pencil
index cards
sheets of paper
bicycle inner tube

Key Concepts

A rocket has a few parts different from an airplane. One of the main differences is the absence of wings. Rockets utilize fins, which help steer the rocket, while airplanes use wings to generate lift. Rocket fins are more like the rudder of an airplane than the wings.

Another difference is the how rockets get their speed. Airplanes generate thrust from a rotating blade, whereas rockets get their movement by squeezing down a high-energy gaseous flow and squeezing it out a tiny exit hole. If you’ve ever used a garden hose, you already know how to make the water stream out faster by placing your thumb over the end of the hose. You’re decreasing the amount of area the water has to exit the hose, but there’s still the same amount of water flowing out, so the water compensates by increasing its velocity. This is the secret to rocket nozzles – squeeze the flow down and out a small exit hole to increase velocity.

The rockets we’re about to build get their thrust by generating enough pressure and releasing that pressure very quickly. You will generate pressure both by pumping and by chemical reaction, which generates gaseous products.

What’s Going On?

For every action, there is equal and opposite reaction. If flames shoot out of the rocket downwards, the rocket itself will soar upwards. It’s the same thing if you blow up a balloon and let it go-the air inside the balloon goes to the left, and the balloon zips off to the right (at least, initially).

Your rocket generates a high pressure by squeezing the air into a very small space and using Bernoulli’s Principles in action! As you stomp on the rocket, the air pressure leaves the bottle pretty quickly, pushing the paper rocket out of the way as it zooms out of the tube. By narrowing the exit diameter, you allow the air to speed up as it exits, creating a higher launch for your rocket.

You can modify your rocket body design. Add more fins, tilt the fins at a angle, or try no fins at all! You can add a more steeply slanted nose. You can cut the rocket body in half or make it twice as long. There’s so many things you can test out, change, or modify with this simple activity! You can also add canards (glider-type wings) to either side of the rocket body right under the nose and turn it into a glider when it starts to fall back to Earth!

Questions to Ask

Does it matter how many fins you use?
What happens if there’s an air leak in the system?
How can you make the rocket fly even higher? Name three different ways.
Is the center of pressure before or aft of the center of gravity on your rocket?
For stable flight, how many fins do you ideally need?
How can you make the rocket spin as it launches?

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Special Science Teleclass: Physics of Motion

Friday February 8, 2019

This is a recording of a recent live teleclass I did with thousands of kids from all over the world. I’ve included it here so you can participate and learn, too!

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Materials:

- Print out this worksheet
- marbles
- masking tape
- 3/4″ pipe foam insulation (NOT neoprene and NOT the kind with built-in adhesive tape)
- 9 popsicle sticks
- 4 rubber bands
- one plastic spoon
- ping pong ball
- hot glue gun with glue sticks

Key Concepts

What’s Going On?

It’s really important to know how much centrifugal force people experience, whether its in cars or roller coasters! In fact roller coaster loops used to be circular, but now they use clothoid loops instead to keep passengers happy during their ride so they don’t need nearly the acceleration that they’d need for a circular loop (which means less g-force so passengers don’t black out).

Here are more roller coaster maneuvers you can try out:

Whirly-Birds: Take a loop and make it horizontal. Great around poles and posts, but just keep the bank angle steep enough and the marble speed fast enough so it doesn’t fly off track.

Troubleshooting

“Hmmm… did the marble go to fast or too slow?”

“Where did it fly off?”

“Wow – I’ll bet you didn’t expect that to happen. Now what are you going to try?”

Become their biggest fan by cheering them on, encouraging them to make mistakes, and try something new (even if they aren’t sure if it will work out).

Questions to Ask

Does the track change position with the weight of the marble, making it fly off course? (You can make the track more rigid by taping it to a surface.)
Is the marble jumping over the track wall? (You can increase your bank angle – the amount of twist the track makes along its length.)
How can you make your marble zip through two loops at once?
How could you increase your marble speed?
Where would you put a tunnel? (Leave one piece of track uncut to use as a tunnel.)

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Seasons

Friday February 8, 2019

The seasons are caused by the Earth’s axis tilt of 23.4o from the ecliptic plane.

Materials

Bright light source (not fluorescent)
Balloon
Protractor
Masking tape
2 liquid crystal thermometers
Ruler, yardstick or meter stick
Marker

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Download Student Worksheet & Exercises

For a light source, try lamps with 100W bulbs (without lamp shades). Make sure there’s room to walk all the way around it. You’ll want to circle the lamp at a distance of about 2 feet away.
Mark on the floor with tape and label the four positions: winter, spring, summer, and fall. They should be at the 12, 3, 6, and 9 o’clock positions. Winter is directly across from summer. The Earth rotates counterclockwise around the Sun when viewed from above.
Blow up your balloon so it’s roughly round-shaped (don’t blow it up all the way). Mark and label the north and south poles with your marker. Draw an equator around the middle circumference.
The Earth doesn’t point its north pole straight up as it goes around the Sun. It’s tilted over 23.4o. here’s how you find this point on your balloon:
1. Put the South Pole mark on the table, with north pointing straight up. Find the midway point between the equator and the North Pole and make a tiny mark. This is the 45o latitude point. You’ll need this to find the 23o mark.
2. Find the midway point between the 45o and the North Pole and make another mark, larger this time and label it with 23o. When this mark is pointing up, the Earth is tilted over the right amount.
3. You’ll need to do this three more times so you can draw a line connecting the dots. You want to draw the latitude line at 23o so you can rotate the balloon as you move around to the different seasons. The line will always be pointed up.
Place the thermometers on the balloon at these locations:
1. Find the halfway point between the South Pole and the equator. Put one thermometer on this mark.
2. Put the other thermometer on the northern hemisphere’s 45o mark from above.
Make sure your lamp is facing the balloon as you stand on summer. Let the balloon be heated by the lamp for a couple of minutes and then record the temperature in the data table.
Rotate the lamp to point to fall. Move your balloon to fall, rotating the balloon so that the thermometers are facing the lamp. Wait a few more minutes and take another reading.
Rotate the lamp to point to winter. Move your balloon to winter, rotating the balloon so that the thermometers are facing the lamp. Wait a few more minutes and take another reading.
Rotate the lamp to point to spring. Move your balloon to spring, rotating the balloon so that the thermometers are facing the lamp. Wait a few more minutes and take another reading. You’ve completed a data set for planets with an axis tilt of about 23o, which includes the Earth, Mars, Saturn and Neptune.
Repeat steps 1-9 for Mercury. Note that Mercury does not have an axis tilt, so the North Pole really points straight up. Jupiter (3.1o axis tilt) and Venus (2.7o) are very similar. The Moon’s axis tilt is 6.7o, so you can approximate these four objects with a 0o axis tilt.
Repeat steps 1-9 for Uranus. Since the axis tilt is 97.8o, you can approximate this by pointing the north pole straight at the Sun during summer (90o axis tilt). The orbit for Uranus is 84 years, which means 21 years passes between each season. The north pole will experience continued sunlight for 42 years from spring through fall, then darkness for 42 years.

What’s Going On?

Exercises

What is the main reason we have seasons on Earth?
Why are there no sunsets on Uranus for decades?
Are there seasons on Venus?

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Liquid Crystals

Friday February 8, 2019

If you’ve completed the Soaking Up Rays experiment, you might still be a bit baffled as to why there’s a difference between black and white. Here’s a great way to actually “see” radiation by using liquid crystal thermal sheets.

You’ll need to find a liquid crystal sheet that has a temperature range near body temperature (so it changes color when you warm it with your hands.)

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The liquid crystal sheet is temperature-sensitive. When the sheet received heat from the bulb, the temperature goes up and changes color. The plastic sheets remain black except for the temperature range in which they display a series of colors that reflect the actual temperature of the crystal.

Materials:

hands
Thermal paper (AKA: Liquid Crystal Sheet)
Incandescent light bulb (or sunny day)
Silver highlighter or aluminum foil

1. Color half of the back side of the thermal paper (the side that doesn’t change color) with the highlighter (or cover half of it with foil).

2. Hold it in a position where you can easily see the color-changing side while keeping the light source on the back side.

3. Which side changes color? Is there a difference between the silver and black halves?

You’ll notice that the black half almost immediately changes color, while the silver side stays black. The silver coating reflects the heat, keeping it cool. The black side absorbs the heat and raises its temperature.

Why do liquid crystals change color with temperature? Your liquid crystal sheet is not just one sheet, but a stack of several sheets that are slightly offset from each other. The distance between each layer changes as the sheet warms up – the hotter the temperature, the closer the stacks twist together. The color they emit depends on the distance between the sheets.

The molecules that make up the sheets are long and thin, like hot dogs. When the sheets are cooler, these molecules move around less and don’t twist up as much, which corresponds to reflecting back a redder light. When the temperature rises, the molecules move around more and twist together, and they reflect a bluer light. When the liquid crystal sheet is black, all the light is absorbed (no light gets reflected).

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Soaking Up Rays

Friday February 8, 2019

Heat is transferred by radiation through electromagnetic waves. Remember, when we talked about waves and energy? Well, heat can be transferred by electromagnetic waves. Energy is vibrating particles that can move by waves over distances right? Well, if those vibrating particles hit something and cause those particles to vibrate (causing them to move faster/increasing their temperature) then heat is being transferred by waves. The type of electromagnetic waves that transfer heat are infra-red waves. The Sun transfers heat to the Earth through radiation.

If you hold your hand near (not touching) an incandescent light bulb until you can feel heat on your hand, you’ll be able to understand how light can travel like a wave. This type of heat transfer is called radiation.

Now don’t panic. This is not a bad kind of radiation like you get from x-rays. It’s infra-red radiation. Heat was transferred from the light bulb to your hand. The energy from the light bulb resonated the molecules in your hand. (Remember resonance?) Since the molecules in your hand are now moving faster, they have increased in temperature. Heat has been transferred! In fact, an incandescent light bulb gives off more energy in heat then it does in light. They are not very energy efficient.

Now, if it’s a hot sunny day outside, are you better off wearing a black or white shirt if you want to stay cool? This experiment will help you figure this out:

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You need:

2 ice cubes, about the same size.
A white piece of paper
A black piece of paper
A sunny day

Download Student Worksheet & Exercises

1. Put the two pieces of paper on a sunny part of the sidewalk.

2. Put the ice cubes in the middle of the pieces of paper.

3. Wait.

What you should eventually see, is that the ice cube on the black sheet of paper melts faster then the ice cube on the white sheet. Dark colors absorb more infra-red radiation then light colors. Heat is transferred by radiation easier to something dark colored then it is to something light colored and so the black paper increased in temperature more then the white paper.

So, to answer the shirt question, a white shirt reflects more infra-red radiation so you’ll stay cooler. White walls, white cars, white seats, white shorts, white houses, etc. all act like mirrors for infra-red (IR) radiation. Which is why you can aim your TV remote at a white wall and still turn on the TV. Simply pretend the wall is a mirror (so you can get the angle right) and bounce the beam off the wall before it gets to your TV. It looks like magic!

Click over to this experiment to learn how to make Liquid Crystals.

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Sensing Temperature

Friday February 8, 2019

Temperature is a way of talking about, measuring, and comparing the thermal energy of objects.

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The words “hot” , “cold”, “warm” and so forth describe what scientists call thermal energy. Thermal energy is how much the molecules are moving inside an object. The faster molecules move, the more thermal energy it has.

Objects that have molecules moving very quickly are said to have high thermal energy or high temperature. Like a cloud of steam, for example. The higher the temperature, the faster the molecules are moving inside that steam cloud.

Temperature is just a speedometer for molecules. The speed of the molecules in ice cream is way slower than it is in a hot shower.

If everything is made of molecules, and these molecules are speeding up and slowing down, what do you think happens if they change speed a lot? Do you think my kitchen table will start vibrating across the room if the table somehow gets too hot?

No, probably not, my table will not start jumping around the room, no matter how hot it gets. It would melt down into a mush first! But some interesting things do happen when molecules change speeds.

There are three common states of matter – I bet you know what they are already: solid, liquid, and gas. Water is really special because it can a solid, liquid or gas state pretty normal temperatures. You don’t need a mad scientist lab to get it to go into any of these three states.

Water is one of the only substances that expands instead of shrinks when it freezes. It’s also a polar molecule, meaning that if you stick a static charge next to it, like a balloon you rubbed on your head, you can get the water to move.

Imagine an icicle. The water is in a solid state when it’s an icicle. It’s holding its shape. The molecules in the water are held together by strong, stiff bonds. These bonds hold the water molecules in a tight pattern called a matrix. This matrix holds the water molecules in a crystalline pattern.

Can you imagine breaking off an icicle and sticking it in a tea kettle on the stove? Now, let’s pretend to turn on the heat. The heat is transferred from the stove to the kettle to the icicle.

What happens to our icicle?

As the icicle absorbs the heat, the molecules begin to vibrate faster (the temperature is increasing). When the molecules vibrate at a certain speed (they gain enough thermal energy) they stretch those strong, stiff matrix crystalline bonds enough that the bonds become more like rubber bands or springs and they stretch and get all loose-goosey.

That’s when the icicle becomes liquid. There are still bonds between the molecules, but they are a bit loose, allowing the molecules to move and flow around each other.

The act of changing from a solid to a liquid is called melting. The temperature at which a substance changes from a solid to a liquid is called its melting point. For water, that point is 32° F or 0° C. (Remember those numbers from the slide with all the temperature scales?)

Now if we continue heating, we see our icicle go from solid to completely liquid, and now we notice bubbling. What’s going on now?

Now the temperature is at 212° F or 100° C and the water is going from a liquid state to a gaseous state. This means that the loosey goosey bonds that connected the molecules before have been stretched as far as they go, can’t hold on any longer and “POW!” they snap.

Those water molecules no longer have any bonds and are free to roam aimlessly around the room (think toddlers). Gas molecules move at very quick speeds as they bounce, jiggle, crash and zip around any container they are in (kind of like toddles on sugar). The act of changing from a liquid to a gas is called evaporation or boiling and the temperature at which a substance changes from a liquid to a gas is called its boiling point.

Now if we turn off the stove, what do you think happens?

Our gaseous water molecules get close to something cool, they will combine and turn from gaseous to liquid state. This is what happens to your bathroom mirror during a shower or bath. The gaseous water molecules that are having fun bouncing and jiggling around the bathroom get close to the mirror. The mirror is colder than the air. As the gas molecules get close they slow down due to loss of temperature. If they slow enough, they form loosey goosey bonds with other gas molecules and change from gas to liquid state.

The act of changing from gas to liquid is called condensation. The temperature at which molecules change from a gas to a liquid is called the condensation point. Clouds are made of hundreds of billions of tiny little droplets of liquid water that have condensed onto particles of some sort of dust.

Now let’s turn the heat down a bit more and see what happens. Imagine we stick the tea kettle in the freezer. As the temperature drops and the molecules continue to slow, the bonds between the molecules can pull them together tighter and tighter.

Eventually the molecules will fall into a matrix, a pattern, and stick together quite tightly. This would be the solid state. The act of changing from a liquid to a solid is called freezing and the temperature at which it changes is called (say it with me now) freezing point.

Think about this for a second – is the freezing point and melting point of an object at the same temperature? Does something go from solid to liquid or from liquid to solid at the same temperature?

If you said yes, you’re right!

The freezing point of water and the melting point of water are both 32° F or 0° C. The temperature is the same. It just depends on whether it is getting hotter or colder as to whether the water is freezing or melting.

The boiling and condensation point is also the same point.

Crazy Temperatures

Here’s an experiment you can do to baffle your senses: Fill one glass with hot water (not boiling), another with ice water, and a third with room temperature water. Place a finger in the hot water and a finger in the ice cold water for a minute or two. Then stick both fingers in the room temperature cup.

How does that feel?

Did it seem that each finger detected a different temperature when placed in the room temperature cup? Weird! So what gives?

Materials:

3 cups of water (see video)
your hands

Download Student Worksheet & Exercises

Your skin contains temperature sensors that work by detecting the direction heat flow (in or out of your body), not temperature directly. These sensors change temperature depending on their surroundings. So when you heated up one finger, and then placed it in cooler water, the heat flowed out of your body, telling your brain it was getting cooler. The ice water finger was detecting a heat flow into your body… and presto! You have one confused brain.

In order for heat to flow, you need to have a temperature difference. Did you notice how your fingers weren’t good thermometers with this experiment? This is why scientists had to invent the thermometer, because the human body isn’t designed to detect temperature, only heat flow.

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Cloud Tracker Weather Instrument

Friday February 8, 2019

One of the most remarkable images of our planet has always been how dynamic the atmosphere is a photo of the Earth taken from space usually shows swirling masses of white wispy clouds, circling and moving constantly. So what are these graceful puffs that can both frustrate astronomers and excite photographers simultaneously?

Clouds are frozen ice crystals or white liquid water that you can see with your eyes. Scientists who study clouds go into a field of science called nephology, which is a specialized area of meteorology. Clouds don’t have to be made up of water – they can be any visible puff and can have all three states of matter (solid, liquid, and gas) existing within the cloud formation. For example, Jupiter has two cloud decks: the upper are water clouds, and the lower deck are ammonia clouds.

We’re going to learn how to build a weather instrument that will record whether (weather?) the day was sunny or cloudy using a very sensitive piece of paper. Are you ready?

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Materials:

Sun print paper or other paper sensitive to light
Film canister or soup can
Drill with drill bit
Scissors
Sunlight

The paper from a sun print kit has a very special coating that makes the paper react to light. Most sun print kits use set of light-sensitive chemicals such as potassium ferricyanide and ferric ammonium citrate to make a cyanotype solution. The paper changes color when exposed to UV light. In fact, you can try exposing the paper to different colors and see which changes the paper the most over a set amount of time!

The last step of this chemical process is to ‘set’ the reaction by washing it in plain water – this keeps the image on the paper so it doesn’t all disappear when you hang it on the wall. After the paper dries, the area exposed to UV light turns blue, and everything shaded turns white.

You can use sun print paper to test how well your sunblock works – just smear your favorite sunscreen over a sheet (or put a couple dabs of each kind) and see how well the paper stays protected: if it turns white, the light is getting through. If it stays blue, the sunscreen blocked the light!

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Rain Gauge

Friday February 8, 2019

Also known as an udometer or pluviometer or ombrometer, or just plan old ‘rain cup’, this device will let you know how much water came down from the skies. Folks in India used bowls to record rainfall and used to estimate how many crops they would grow and thus how much tax to collect!

These devices reports in “millimeters of rain” or “”centimeters of rain” or even inches of rain”. Sometimes a weather station will collect the rain and send in a sample for testing levels of pollutants.

While collecting rain may seem simple and straightforward, it does have its challenges! Imagine trying to collect rainfall in high wind areas, like during a hurricane. There are other problems, like trying to detect tiny amounts of rainfall, which either stick to the side of the container or evaporate before they can be read on the instrument. And what happens if it rains and then the temperature drops below freezing, before you’ve had a chance to read your gauge? Rain gauges can also get clogged by snow, leaves, and bugs, not to mention used as a water source for birds.

So what’s a scientist to do?

Press onward, like all great scientists! And invent a type of rain gauge that will work for your area. We’re going to make a standard cylinder-type rain gauge, but I am sure you can figure out how to modify it into a weighing precipitation type (where you weigh the amount in the bottle instead of reading a scale on the side), or a tipping bucket type (where a funnel channels the rain to a see-saw that tips when it gets full with a set amount of water) , or even a buried-pit bucket (to keep the animals out).
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Materials:

two water bottles
scissors
rainy day (or use water)

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Thermometer

Friday February 8, 2019

First invented in the 1600s, thermometers measure temperature using a sensor (the bulb tip) and a scale. Temperature is a way of talking about, measuring, and comparing the thermal energy of objects. We use three different kinds of scales to measure temperature. Fahrenheit, Celsius, and Kelvin. (The fourth, Rankine, which is the absolute scale for Fahrenheit, is the one you’ll learn about in college.)

Mr. Fahrenheit, way back when (18th century) created a scale using a mercury thermometer to measure temperature. He marked 0° as the temperature ice melts in a tub of salt. (Ice melts at lower temperatures when it sits in salt. This is why we salt our driveways to get rid of ice). To standardize the higher point of his scale, he used the body temperature of his wife, 96°.

As you can tell, this wasn’t the most precise or useful measuring device. I can just imagine Mr. Fahrenheit, “Hmmm, something cold…something cold. I got it! Ice in salt. Good, okay there’s zero, excellent. Now, for something hot. Ummm, my wife! She always feels warm. Perfect, 96°. ” I hope he never tried to make a thermometer when she had a fever.

Just kidding, I’m sure he was very precise and careful, but it does seem kind of weird. Over time, the scale was made more precise and today body temperature is usually around 98.6°F.

Later, (still 18th century) Mr. Celsius came along and created his scale. He decided that he was going to use water as his standard. He chose the temperature that water freezes at as his 0° mark. He chose the temperature that water boils at as his 100° mark. From there, he put in 100 evenly spaced lines and a thermometer was born.

Last but not least Mr. Kelvin came along and wanted to create another scale. He said, I want my zero to be ZERO! So he chose absolute zero to be the zero on his scale.

Absolute zero is the theoretical temperature where molecules and atoms stop moving. They do not vibrate, jiggle or anything at absolute zero. In Celsius, absolute zero is -273 ° C. In Fahrenheit, absolute zero is -459°F (or 0°R). It doesn’t get colder than that!

As you can see, creating the temperature scales was really rather arbitrary:

“I think 0° is when water freezes with salt.”
“I think it’s just when water freezes.”
“Oh, yea, well I think it’s when atoms stop!”

Many of our measuring systems started rather arbitrarily and then, due to standardization over time, became the systems we use today. So that’s how temperature is measured, but what is temperature measuring?

Temperature is measuring thermal energy which is how fast the molecules in something are vibrating and moving. The higher the temperature something has, the faster the molecules are moving. Water at 34°F has molecules moving much more slowly than water at 150°F. Temperature is really a molecular speedometer.

Let’s make a quick thermometer so you can see how a thermometer actually works:

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Materials:

plastic bottle
straw
hot glue or clay
water
food coloring
rubbing alcohol
index card and pen

When something feels hot to you, the molecules in that something are moving very fast. When something feels cool to you, the molecules in that object aren’t moving quite so fast. Believe it or not, your body perceives how fast molecules are moving by how hot or cold something feels. Your body has a variety of antennae to detect energy. Your eyes perceive certain frequencies of electromagnetic waves as light. Your ears perceive certain frequencies of longitudinal waves as sound. Your skin, mouth and tongue can perceive thermal energy as hot or cold. What a magnificent energy sensing instrument you are!

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Hygrometer

Friday February 8, 2019

Hygrometers measure how much water is in the air, called humidity. If it's raining, it's 100% humidity. Deserts and arid climates have low humidity and dry skin. Humidity is very hard to measure accurately, but scientists have figured out ways to measure how much moisture is absorbed by measuring the change in temperature (as with a sling psychrometer), pressure, or change in electrical resistance (most common).

The dewpoint is the temperature when moist air hits the water vapor saturation point. If the temperature goes below this point, the water in the air will condense and you have fog. Pilots look for temperature and dewpoint in their weather reports to tell them if the airport is clear, or if it''s going to be 'socked in'. If the temperature stays above the dewpoint, then the airport will be clear enough to land by sight. However, if the temperature falls below the dewpoint, then they need to land by instruments, and this takes preparation ahead of time.

A sling psychrometer uses two thermometers (image above), side by side. By keeping one thermometer wet and the other dry, you can figure out the humidity using a humidity chart. Such as the one on page two of this document. The psychrometer works because it measures wet-bulb and dry-bulb temperatures by slinging the thermometers around your head. While this sounds like an odd thing to do, there's a little sock on the bottom end of one of the thermometers which gets dipped in water. When air flows over the wet sock, it measures the evaporation temperature, which is lower than the ambient temperature, measured by the dry thermometer.

Scientists use the difference between these two to figure out the relative humidity. For example, when there's no difference between the two, it's raining (which is 100% humidity). But when there's a 9^oC temperature difference between wet and dry bulb, the relative humidity is 44%. If there's 18^oC difference, then it's only 5% humidity.

You can even make your own by taping two identical thermometers to cardboard, leaving the ends exposed to the air. Wrap a wet piece of cloth or tissue around the end of one and use a fan to blow across both to see the temperature difference!

One of the most precise are chilled mirror dewpoint hygrometers, which uses a chilled mirror to detect condensation on the mirror's surface. The mirror's temperature is controlled to match the evaporation and condensation points of the water, and scientists use this temperature to figure out the humidity.

We're going to make a very simple hygrometer so you get the hand of how humidity can change daily. Be sure to check this instrument right before it rains. This is a good instrument to read once a day and log it in your weather data book.

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Materials:

single hair
index card
tack
cardboard
tape
scissors
dime

This device works because human hair changes length with humidity, albeit small. We magnify this change by using a lever arm (the arrow and mark the different places on the cardboard to indicate levels of humidity. Does all hair behave the same way? Does it matter if you use curly or straight hair, or even the color of the hair? Does gray work better than blonde?

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Barometer

Friday February 8, 2019

French physicist Blaise Pascal. He developed work on natural and applied sciences as well being a skilled mathematician and religious philosopher.

A barometer uses either a gas (like air) or a liquid (like water or mercury) to measure pressure of the atmosphere. Scientists use barometers a lot when they predict the weather, because it’s usually a very accurate way to predict quick changes in the weather.

Barometers have been around for centuries – the first one was in the 1640s!

At any given momen, you can tell how high you are above sea level by measure the pressure of the air. If you measure the pressure at sea level using a barometer, and then go up a thousand feet in an airplane, it will always indicate exactly 3.6 kPa lower than it did at sea level.

Scientists measure pressure in “kPa” which stands for “kilo-Pascals”. The standard pressure is 101.3 kPa at sea level, and 97.7 kPa 1,000 feet above sea level. In fact, every thousand feet you go up, pressure decreases by 4%. In airplanes, pilots use this fact to tell how high they are. For 2,000 feet, the standard pressure will be 94.2 kPa. However, if you’re in a low front, the sea level pressure reading might be 99.8 kPa, but 1000 feet up it will always read 3.6 kPa lower, or 96.2 kPa.

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Materials:

balloon
straw or stick
water glass or clean jam jar
index card
tape

At standard pressure, depending on the kind of barometer you have, you’ll find they all read one of these: 101.3 kPa; 760 mmHg (millimeters of mercury, or “torr”); 29.92 inHg (inches of mercury); 14.7 psi (pounds per square inch); 1013.25 millibars/hectopascal. They are all different unit systems that all say the same thing.

Just like you can have 1 dollar or four quarters or ten dimes or 20 nickels or a hundred pennies, it’s still the same thing.

Why does water boil differently at sea level than it does on a mountain top?

It takes longer to cook food at high altitude because water boils at a lower temperature. Water boils at 212^oF at standard atmospheric pressure. But at elevations higher than 3,500 feet, the boiling point of water is decreased.

The boiling point is defined when the temperature of the vapor pressure is equal to the atmospheric pressure. Think of vapor pressure as the pressure made by the water molecules hitting the inside of the container above the liquid level. But since the saucepan of water is not sealed, but rather open to the atmosphere, the vapor simply expands to the atmosphere and equals out. Since the pressure is lower on a mountaintop than at sea level, this pressure is lower, and hence the boiling point is lowered as well.

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Anemometer

Friday February 8, 2019

Most weather stations have anemometers to measure wind speed or wind pressure. The kind of anemometer we’re going to make is the same one invented back in 1846 that measures wind speed. Most anemometers use three cups, which is not only more accurate but also responds to wind gusts more quickly than a four-cup model.

Some anemometers also have an aerovane attached, which enables scientists to get both speed and direction information. It looks like an airplane without wings – with a propeller at the front and a vane at the back.

Other amemometers don’t have any moving parts – instead they measure the resistance of a very short, thin piece of tungsten wire. (Resistance is how much a substance resists the flow of electrical current. Copper has a low electrical resistance, whereas rubber has a very high resistance.) Resistance changes with the material’s temperature, so the tungsten wire is heated and placed in the airflow. The wind flowing over the wire cools it down and increases the resistance of the wire, and scientists can figure out the wind speed.

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Scientists also use sonic anemometers, which use ultrasonic waves to detect wind speed. The great thing about sonic anemometers is that they can measure speed in all three directions, which is great for studying wind that is not all moving in the same direction (like gusts and hurricanes).

Sonic anemometers send a sound wave from one side to the other and measure the time it takes to travel. Which means that these can also be used as thermometers, as temperature will also change the speed of sound. Since there are no moving parts, you’ll find these types of anemometers in harsh conditions, like on a buoy or in the desert, where salt disintegrates and dust gets in the way of the cup-style anemometer. The big drawback to sonic anemometers is water (like dew or rain): if the transducers get wet, it changes the speed of sound and gives an error in the reading.

The quickest anemometer to make is to attach the end of a string (about 12″ long) to a ping pong ball. Suspend the string in the wind, like from a fan or hair dryer (use the ‘cool’ setting). Since the ball is so lightweight, it’s quite responsive to wind speed.

Add a protractor flipped upside down (so you can measure the angle of the string). Use the measurements below to figure out the wind speed. For example, mark the 90^o angle with “0 mph”. This is your ping pong ball at rest in no wind. Use the numbers below to make the rest:

Angle	Wind Speed
degrees	mph
90	0
80	8
70	12
60	15
50	18
40	21
30	26
20	33

Now let’s make a four-cup anemometer. Here’s what you need to do:

Materials:

four lightweight cups
two sticks or popsicle sticks
tape or hot glue
tack or pin
pencil with eraser on top
block of foam (optional)

How steady was the wind that you measured? If you place your anemometer next to a door or a window, is there wind? How fast? Where could you place your anemometer so you can quickly read it each day?

By making two anemometers, one that you already know what the wind speed is, you can easily figure out how to calibrate the other. For example, how fast do the cups fly around when the ping pong ball anemometer indicates 12 mph? Can you see each cup, or are they a blur? You’ll get a feel for how to read the four-cup model by eye once you’ve had practice.

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Introduction to Creating a Homemade Weather Station

Friday February 8, 2019

Being able to predict tomorrow’s weather is one of the most challenging and frequently requested bits of information to provide. Do you need a coat tomorrow? Will soccer practice be canceled? Will the crops freeze tonight?

Scientists use different instruments to record the current weather conditions, like temperature, barometric pressure, wind speed, humidity, etc. The real work comes in when they spend time looking over their data over days, months, even years and search for patterns.

But where does the weather station get its weather from?

One of the greatest leaps in meteorology was using numbers to predict the flow of the atmosphere. The math equations needed for these (using fluid dynamics and thermodynamics) are enough to make even a graduate student quiver with fear. Even today’s most powerful computers cannot solve these complex equations! The best they can do is make a guess at the solution and then adjust it until it fits well enough in a given range. How do the computers know what to guess?

Several weather stations around the world work together to report the current weather every hour. These stations can be land-based, mounted on buoys in the ocean, or launched on radiosondes and report back to a home station as they rise through the different layers of the atmosphere. Pilots will also give weather reports en route to their destination, which get recorded and added to the database of weather knowledge.

We’re going to build our own homemade weather station and start keeping track of weather right in your own home town. By keeping a written record (even if it’s just pen marks on the wall), you’ll be able to see how the weather changes and even predict what it will do, once you get the hang of the pattern in your local area. For example, if you live in Florida, what happens to the pressure before the daily afternoon thunderstorm? Or if you live in the deserts of Arizona, what does a sudden increase in humidity tell you?
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This is an introductory video that will get you started making your own weather station:

Once you have your weather station up and working, you can make another and send set it up at a friend’s house or a distant relative. Ask them to read you the instruments when you call them so you can have more than one weather tracking station!

By understanding how the atmosphere moves and changes, scientists can guess on what it will do tomorrow based on what it’s done in the past. Even with our massive super-computers today, people are still required to make certain calculations and decisions as to which set of math equations best fit (model) what the weather’s currently doing. Maybe one day computers will be able to do this, but we’re not there yet.
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Special Science Teleclass: Thermodynamics

Friday February 8, 2019

This is a recording of a recent live teleclass I did with thousands of kids from all over the world. I’ve included it here so you can participate and learn, too!

You’ll discover how to boil water at room temperature, heat up ice to freeze it, make a fire water balloon, and build a real working steam boat as you learn about heat energy. You’ll also learn about thermal energy, heat capacity, and the laws of thermodynamics.

Materials:

cup of ice water
cup of room temperature water
cup of hot water (not scalding or boiling!)
tea light candle and lighter (with adult help)
balloon (not inflated)
syringe (without the needle)
block of foam
copper tubing (¼” diameter and 12” long)
bathtub or sink
scissors or razor
fat marker (to be used to wrap things around, not for writing)

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Key Concepts

The terms hot, cold, warm etc. describe what physicists call thermal energy. Thermal energy is how much the molecules are moving inside an object. The faster molecules move, the more thermal energy that object has.

There are three different scales for measuring temperature. Fahrenheit, Celsius and Kelvin. (There’s also a fourth temperature scale for absolute Fahrenheit called Rankine.) Temperature is basically a speedometer for molecules. The faster they are wiggling and jiggling, the higher the temperature and the higher the thermal energy that object has. Your skin, mouth and tongue are antennas which can sense thermal energy.

There are four states of matter: Solid, liquid, gas and plasma. Solids have strong, stiff bonds between molecules that hold the molecules in place. Liquids have loose, stringy bonds between molecules that hold molecules together but allow them some flexibility. Gasses have no bonds between the molecules. Plasma is similar to gas but the molecules are very highly energized. Materials can change from one state to another depending on the temperature and the bonds. Changing from a solid to a liquid is called melting. Changing from a liquid to a gas is called boiling, evaporating, or vaporizing. Changing from a gas to a liquid is called condensation. Changing from a liquid to a solid is called freezing. All materials have given points at which they change from state to state. Melting point is the temperature at which a material changes from solid to liquid. Boiling point is the temperature at which a material changes from liquid to gas. Condensation point is the temperature at which a material changes from gas to liquid. Freezing point is the temperature at which a material changes from liquid to gas.

What’s Going On?

Heat is the movement of thermal energy from one object to another. Heat can only flow from an object of a higher temperature to an object of a lower temperature (this is the First Law of Thermodynamics). Heat is movement of thermal energy from one object to another. When an object absorbs heat it does not necessarily change temperature. Objects release heat as they freeze and condense. Objects absorb heat as they evaporate and melt. Freezing points, melting points, boiling points and condensation points are the “speed limits” of the phases. Once the molecules reach that speed they must change state.

Heat capacity is how much heat an object can absorb before its temperature increases. Specific heat is how much heat energy a mass of a material must absorb before it increases 1°C. Heat capacity is influenced by the specific heat of the material and/or the amount of the material. Each material has its own specific heat. The higher a material’s specific heat is, the more heat it must absorb before its temperature increases. A larger amount of something will have a higher heat capacity then a smaller amount of something. Water has a very high heat capacity.

Questions:

True or False: Water is poor at absorbing heat energy.
True or False: A molecule that heats up will move faster.
True or False: A material will be less dense at lower temperatures.
For gases, if we increase the temperature, what happens to the pressure and the volume?
What is specific heat?
What is heat?
Does heat flow from cold to hot? Give an example.
What do the our body sense, heat flow or temperature? Are they the same thing?
How can we boil room temperature water without heating up the water?

Answers:

False.
True.
False. (Usually.)
If we increase the temperature, the pressure increases and the volume decreases. This is called the Ideal Gas Law (remember the ping pong balls from the teleclass?)
Specific heat is how much heat energy a mass of a material must absorb before it increases 1°C.
Heat is the movement of thermal energy from one object to another.
No. Heat flows from hot to cold. (This is the First Law of Thermodynamics.) A hot cup of coffee left out on a cold morning will eventually cool to the surrounding air temperature.
Heat flow. No they are not the same thing. Temperature is a measure of how much energy the molecules have.
By increasing the pressure by decreasing the volume, we can force the bubbles out of the water and it will boil. Boiling is when the liquid water turns into a gas, NOT when the liquid water heats up. Boiling can happen at many different temperatures when you change the pressure.

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Can the Sun Be Used to Heat Water?

Friday February 8, 2019

Solar energy is still more expensive than other methods of generating electricity. However, the cost of solar electricity has greatly decreased since the first solar cells were developed in 1954.

Paint brush
Thermometer (outdoor type)
Newspaper
Aluminum foil
Water
Large, plastic glass
Empty aluminum 12-ounce (355 milliliter) soft drink can
Black paint or spray paint (flat, not shiny)

Download Student Worksheet & Exercises

Set the black can outside in a sunny spot. Pick a place where the sun will shine on the can all day. (You do not want the can to be in the shade.)

Observations

Discussion

Other Things to Try

Repeat this experiment with an unpainted can and a painted can. After one hour, how do the temperatures of the water in each can compare?

Repeat this experiment on a cloudy day. Does the water in the can get as hot without sunshine?

Exercises

The solar energy that hits the earth is responsible for what proportion of the energy on our planet?
1. Nearly all of it
2. About 50%
3. 25%
4. None of these
Name one way that the physical earth uses the earth’s energy:
True or false: Solar power is generally less expensive than other forms of power.
1. True
2. False

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Can Wind Be Used as a Source of Energy?

Friday February 8, 2019

The United States has large reserves of coal, natural gas, and crude oil which is used to make gasoline. However, the United States uses the energy of millions of barrels of crude oil every day, and it must import about half its crude oil from other countries.

Burning fossil fuels (oil, coal, gasoline, and natural gas) produces carbon dioxide gas. Carbon dioxide is one of the main greenhouse gases that may contribute to global warming. In addition, burning coal and gasoline can produce pollution molecules that contribute to smog and acid rain.

Using renewable energy-such as solar, wind, water, biomass, and geothermal-could help reduce pollution, prevent global warming, and decrease acid rain. Nuclear energy also has these advantages, but it requires storing radioactive wastes generated by nuclear power plants. Currently, renewable energy produces only a small part of the energy needs of the

United States. However, as technology improves, renewable energy should become less expensive and more common.

Hydropower (water power) is the least expensive way to produce I electricity. The sun causes water to evaporate. The evaporated water falls to the earth as rain or snow and fills lakes. Hydropower uses water stored in lakes behind dams. As water flows through a dam, the falling water turns turbines that run generators to produce electricity.

Currently, geothermal energy (heat inside the earth), biomass (energy from plants), solar energy (light from concentrated sunlight), and wind are being used to generate electricity. For example, in California there are more than sixteen thousand (16,000) wind turbines that generate enough power to supply a city the size of San Francisco with electricity.

In addition to producing more energy, we can also help meet our energy needs through conservation. Conservation means using less energy and using it more efficiently.

In the following experiments, you will use wind to do work, examine how batteries can store energy, and see how insulation can save energy.
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Materials

Pinwheel (can be purchased or madefrom construction paper)
Paper clips
Tape
Small shoe box (children’s size)
Electric fan
Lightweight string (about 4 feet long)
Plastic straw (longer than the width of the shoe box)
Hole punch

Download Student Worksheet & Exercises

Procedure

In this activity, you will try to use the energy in the wind to lift a set of six paper clips. You will first need to construct your windmill.

Use a hole punch to punch holes in the opposite sides across the width of a small, cardboard shoe box. Use the narrow sides of the box so the two holes are less than six inches (15 centimeters) apart. Make sure the holes are directly opposite each other. Place a plastic straw through the two holes. You may need to use the hole punch to enlarge the holes so the straw can rotate within the holes. The ends of the straw should extend out either side of the box.

Use the blades from a purchased pinwheel, or cut and fold a square piece of construction paper into the shape of a pinwheel. Next you will need to attach the pinwheel blades to one end of the straw. Partially unfold a small paper clip and insert the larger end into the straw. Push the straightened end of the paper clip through the center of the pinwheel. Bend this end of the paper clip and tape it to the outside of the pinwheel.

Set the electric fan on a table or countertop. Hold the shoe box so that the pinwheel is free to turn. HAVE AN ADULT PLUG IN AND TURN ON THE FAN. Move the windmill box to direct the breeze from the fan toward the blades of the pinwheel. Move the box until you find the best angle of the fan to the pinwheel so that the pinwheel turns freely and rapidly.

Turn off the fan. Now tape one end of the string to the side of the straw with no pinwheel just outside the box, and wrap the string around the straw a few times. Tie the other end of the string to a paper clip. Attach five other paper clips to the paper clip tied to the string. Allow the string to hang down so that the paper clips on the end of the string rest on the floor.

Now, you will test to see if your windmill can convert wind power to do work and lift the paper clips off the ground. Turn on the fan and hold the box where you did before to make the pinwheel turn.

Observations

Does the windmill turn the straw? Does the string wrap around the straw as the straw turns? What happens to the paper clips?

Discussion

You should observe the straw shaft turning as the wind from the fan is directed toward the blades of the pinwheel. As the pinwheel turns, it should wrap the string around the straw and lift the paper clips into the air. Your windmill converts the energy of the wind to work and lifts the weight of the paper clips. If your windmill is not working, then examine all the parts.

Compare your setup to the drawing, and see if any changes need to be made in your construction.

One way to store the energy produced by a windmill is to lift a weight. When the weight is allowed to fall, work can be produced. Weights in a grandfather clock are used to store energy and can run a clock for a week or longer. A windmill’s energy can be used to pump water to a storage area at a higher elevation. Later, this water can be allowed to fall through a turbine which turns a generator and produces electricity.

Electricity can also be produced directly from wind power. The shaft, or rod to which the windmill blades are attached, can be used to turn a generator. A generator or dynamo is used to convert mechanical energy into electrical energy. Power conversion units can change the direct current that wind generates to an alternating current. The alternating current can be fed directly into utility lines and used in our homes.

The sun is the original source of wind power. Without the sun to heat the earth, there would be no wind. The energy of the sun heats the earth, but all parts of the earth are not at the same temperature. These differences in temperature are responsible for global and local patterns of wind. For example, during the day a constant wind blows from the sea toward the land along coastal regions. Air above the hotter land rises and cooler, heavier air above the ocean moves in to take its place.

The power of the wind can be harnessed to do work. For at least 4,000 years, the wind has been used to move sailing ships. The wind has enough power to move ships across oceans and around the world.

For at least 1,000 years, windmills have been used for pumping water and turning

stones to grind grain. Millions of windmills have been used on the plains of America, Africa, and Australia to pump water from deep wells for livestock and humans.

In this century, windmills or wind engines have been used to generate electricity. Over 15,000 wind engines were installed in California in the 1980s. These wind engines have the capability to produce up to 1.5 billion watts of electricity. In California in 1987, wind was used to produce as much electricity as the city of San Francisco uses in an entire year.

Other Things to Try

Repeat this experiment and find the maximum weight you can lift with your windmill. Try more paper clips or try a heavier weight such as a pen.

List some of the problems associated with using windmills. What happens when the wind is blowing too gently? What happens if the wind blows strongly, such as in a storm? Do you think the area where you live is windy enough for wind engines to produce electricity?

Exercises

Name three sources of renewable energy:
What does the sun have to do with wind?
Name three examples of wind power in historical or current usage:

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How Can Water Be Used to Store Heat Energy?

Friday February 8, 2019

Temperature is a measure of the average hotness of an object. The hotter an object, the higher its temperature. As the temperature is raised, the atoms and molecules in an object move faster. The molecules in hot water move faster than the molecules in cold water. Remember that the heat energy stored in an object depends on both the temperature and the amount of the substance. A smaller amount of water will have less heat energy than a larger amount of water at the same temperature.

Increasing the temperature of a large body of water is one way to store heat energy for later use. A large container filled with salt water, called brine, may be used to absorb heat energy during the day when it is warm. This energy will be held in the salt water until the night when it is cooler. This stored heat energy can be released at night to warm a house or building. This is one way to store the sun’s heat energy until it is needed.

Solar ponds are used to store energy from the sun. Temperatures close to 100°C (212°F) have been achieved in solar ponds. Solar ponds contain a layer of fresh water above a layer of salt water. Because the salt water is heavier, it remains at the bottom of the pond-even as it gets quite hot. A black plastic bottom helps absorb solar energy from sunlight. The water on top serves to insulate and trap the heat in the pond.

In a fresh water pond, as the water on the bottom is heated from sunlight, the hot water becomes lighter and rises to the top of the pond. This convection or movement of hot water to the top tends to carry away excess heat. However, in a salt water pond, there is no convection so heat is trapped. In Israel a series of salt water, solar ponds were developed around the Dead Sea. The heat stored in these solar ponds has been used to run turbines and generate electricity.
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Materials

Two paper cups
Measuring cups
Hot water
Watch or clock
Sink
Refrigerator (with freezer compartment)

Download Student Worksheet & Exercises

Procedure

Turn on the hot water faucet of a sink and wait several minutes until the water is hot. Be careful not to burn yourself with this hot water. Add one-fourth cup of this hot water to the first paper cup. Add one cup of hot water to the second paper cup. Place both of these cups in the freezer compartment of a refrigerator.

After thirty minutes check the water in each cup. Return the cups to the freezer compartment and check them again after fifteen minutes. Keep checking the cups each fifteen minutes until the water in one of the cups is frozen.

Observations

Does the water in the cups freeze at the same time? Does the water in one of the cups freeze first? How long does it take for the water to freeze?

Discussion

You will probably observe that the smaller amount of water in the first cup freezes prior to the larger amount of water in the second cup. Both cups were filled with the same hot water. However, even though the water in both cups was at the same temperature, they did not freeze at the same time. The amount of heat energy stored by the water depends on both the temperature and the amount of water.

We expect that the more heat energy stored in the cup, the longer it takes the water in the cup to freeze. Since one cup of water has more heat energy than one-fourth cup of water, it takes the larger amount of water longer to freeze.

Other Things to Try

Place one-half cup of hot tap water in one cup. Place one-half cup of cool tap water in a second cup. Put both cups in the freezer compartment of a refrigerator and check them every fifteen minutes until the water freezes solid. Which cup of water do you think has more heat energy? Which cup of water do you think will freeze first?

Place one cup of water in one paper cup and one-fourth cup of water in a second paper cup. Put both cups in the freezer of a refrigerator and leave overnight. The next day remove both cups of frozen water. Set the two cups out in the room. Observe the time it takes each piece of ice to melt. Which piece of ice do you think will melt first? Which piece will require more heat energy to cause it to melt?

Exercises

What type of heat transfer is at work in a solar pond?
1. Kinetic
2. Conduction
3. Potential
4. Convection
5. Radiation
What units do we use to measure energy?
1. Kilowatts
2. Joules
3. Newtons
4. Kilowatt-hours
Draw a diagram of a solar pond in the space below:

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How Much Energy Does the Sun Produce?

Friday February 8, 2019

Without the sun, there would be no life on Earth. The sun warms the earth, generates wind, and carries water into the air to produce rain and snow. The energy of the sun provides sunlight for all the plant life on our planet, and through plants provides energy for all animals.

The sun is like a giant furnace in which hydrogen nuclei (atoms without electrons) are constantly smashed together to form helium nuclei. This process is called nuclear fusion. In this process, 3.6 billion kilograms (8 billion pounds) of matter are converted to pure energy every second. The temperature in the sun exceeds 15 million degrees.

Nuclear fusion is one kind of energy. Other forms of energy include: mechanical energy, heat, electrical energy, chemical energy, and light. Mechanical energy is the energy of organized motion, such as a turning wheel. Heat is the energy of random motion, such as a cup of hot water. Electrical energy is the energy of moving charged particles or electrons, such as a current in a wire. Chemical energy is the energy stored in bonds that hold atoms together. Light is any form of electromagnetic waves, such as X rays, microwaves, radio waves, ultraviolet light, or visible light.

Energy can be converted from one from to another. For example, the nuclear energy of the sun is converted to light, which goes through space to the earth. Solar collectors of mirrors can be used to focus some of that light to heat water to steam. This steam can be used to turn a turbine, which can power a generator to produce electricity.

Most of our energy needs are met by burning fossil fuels such as coal, oil, gasoline, and natural gas. The chemical energy stored in these substances is released by burning these fuels. When fossil fuels burn, they combine with oxygen in the air and produce heat and light.

Fossil fuels are not renewable. When they are used up, they are gone forever. However, renewable energy sources such as wind, sun, geothermal, biomass and water power are renewable. They can be used over and over to generate the energy to run our society.

Tremendous amounts of renewable energy are available. For example, the solar energy that falls on just the road surfaces in the United States is equal to the entire energy needs of the country. Although there are sufficient amounts of renewable energy, we must improve our methods of collecting, concentrating, and converting renewable energy into useful forms.

In the following experiments, you will learn something about the amount of energy the sun produces at the earth’s surface and how heat energy can be stored.
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Materials

Water
Disposable, aluminum pie pan
Paint brush
Measuring cups
Watch or clock
Newspaper
Black paint or spray paint (flat, not shiny)

Procedure

Go outside and spread out a sheet of newspaper. Place an aluminum pie pan on the newspaper. Carefully bend one spot on the edge of the pie pan to make a spout shape. This will allow you to more easily pour water out of the pan. Have an adult help you paint the inside of the aluminum pie pan. You can use a brush and a can of paint or spray paint. Be sure not to get the paint on anything except the disposable pie pan and the newspaper. After painting, set the pie pan where the paint can dry overnight.

You will need to do the rest of this experiment on a warm, sunny day. You do not want the pie pan to be in the shade. Set the aluminum pie pan in a warm, sunny spot. The sun will need to constantly shine on the pie pan. The black color of the pie pan allows it to absorb, rather than reflect, solar energy. You will need to begin the experiment about

11:00 A.M., so the solar heating will be done when the sun is high in the sky.

Add exactly one cup of water to the pie pan. Wait four hours while the sun is shining on the pan of water. After exactly four hours of sunshine, carefully pour the remaining water from the pie pan into a one-half or one-fourth measuring cup. Use these measuring cups to estimate the amount of remaining water to the nearest one-eighth of a cup.

Observations

Is the amount of water in the pie pan less than when you began the experiment? How much water is left in the pie pan after four hours of sunlight?

Discussion

You will probably observe that the amount of water in the pie pan is less after four hours of sunlight exposure. Where did the water go? As the sunlight shines on the dark surface of the painted pie pan, solar energy is absorbed and heats the pan and the water. This energy causes a portion of the water to evaporate. As water evaporates, it leaves the liquid form and goes into the air as a gas (water vapor). You will probably find that some, but not all, of the water evaporated.

Scientists use the unit of joule as a measure of energy. However, you may find it helpful to think in units of dietary calories instead of joules. One dietary calorie is equal to 4,184 joules of energy. One cup of breakfast cereal with one-half cup of milk would have about 240 dietary calories, or approximately 1,000,000 joules of energy. Although the earth receives only a tiny portion of the total energy output of the sun, the earth has a constant supply of 173 million billion (173,000,000,000,000,000) watts of solar power. A watt is a unit of power equal to a joule of energy used per second. For comparison, a typical light bulb to run a lamp in your home might require 100 watts of power. A million watts could supply the energy needs of about 500 average American homes.

Use the table below to determine the solar energy required to evaporate a certain amount of water. The amount of water remaining in the pan will allow you to determine how much energy was used, how much power was used, and the amount of power per area.

Your results will probably be in the middle range of this table. For example, if one-half of your water evaporated, then the water remaining would be one-half cup. Thus, the energy used to evaporate this water would be 289,000 joules of energy. This energy would give a power of 20 watts, and a power per area of 800 watts per square meter (watts / meter²).

Solar Energy Required to Evaporate Water
Water Remaining (cup)	Water Evaporated (cup)	Energy Used (joules)	Power Used (watts)	Power per Area (watts / meter²⁾
1	0	0	0	0
7/8	1/8	72,250	5	200
3/4	1/4	144,500	10	400
5/8	3/8	216,750	15	600
1/2	1/2	289,000	20	800
3/8	5/8	361,250	25	1000
1/4	3/4	433,500	30	1200
1/8	7/8	505,750	35	1400
0	1	578,000	40	1600

The following procedure was used to generate the numbers in the Table. It is known that it takes 578,000 joules of energy to evaporate one cup of water. This known energy per cup is multiplied by the fraction of a cup that was evaporated. This gives the solar energy used to evaporate the water in the pie pan. The energy is divided by the number of seconds in four hours (14,400 seconds). This gives the power of the solar energy striking the pie pan, since a watt is equal to a joule per second. Finally, the power (in watts) is divided by the surface area of the pie pan (0.025 square meters) to give the power per area.

When the sun is overhead, the intensity of solar energy can be as much as 1,000 watts per square meter. If all of this energy could be converted to electricity, one square meter of sunshine would be enough to run ten 100-watt light bulbs. However, our current solar cells that convert sunlight to electricity are able to change only about 15 percent of the light to electricity.

You can see from this experiment that there is tremendous energy available from our sun. Most of this energy warms our planet or is reflected back into space. Among other things, the remaining portion of energy powers our water cycle, producing rain and snow, or provides plants with the energy they need to live.

Scientists and engineers are learning more about trapping solar energy and converting it to useful power. It has been estimated that all forms of potentially available renewable energy (wind, water, biomass, and direct solar) have an energy equivalent to 80 trillion barrels of oil. In other words, one year of renewable solar energy is 5,000 times greater than the current yearly energy needs of the United States. In comparison, it has been estimated that all the remaining coal, oil, natural gas, and other potential nonrenewable energy reserves of the United States are equal to about 8 trillion barrels of oil.

Since we do not yet know how to use a significant portion of this renewable energy, much work remains to be done. In the remainder of this book you will learn more about our current ability to use renewable energy and the promise it may hold for the future.

Other Things to Try

Repeat this experiment using different amounts of water on different days and compare the solar power you find.

Repeat this experiment in the late afternoon, when the sun is lower in the sky. How do your result compare to this experiment?
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