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 19th 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:


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

Answers:


  1. How many poles do magnets have, and what are they? Two. North and South poles.
  2. What happens when you bring two like poles together? They repel each other.
  3. 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.
  4. Is the magnetic force stronger or weaker the closer a magnet gets to another magnet? Stronger.
  5. What kinds of materials are magnets made from? Iron, nickel and cobalt.
  6. Name three objects that stick to a magnet. Paperclips, pipe cleaners, and staples.
  7. Name three that don’t stick to a magnet. US quarter, glass, plastic.
  8. 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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A ferrofluid becomes strongly magnetized when placed in a magnetic field. This liquid is made up of very tiny (10 nanometers or less) particles coated with anti-clumping surfactants and then mixed with water (or solvents). These particles don’t “settle out” but rather remain suspended in the fluid.


The particles themselves are made up of either magnetite, hematite or iron-type substance.


Ferrofluids don’t stay magnetized when you remove the magnetic field, which makes them “super-paramagnets” rather than ferromagnets. Ferrofluids also lose their magnetic properties at and above  their Curie temperature points.


Ferrofluids are what scientists call “colloidal suspensions”, which means that the substance has properties of both solid metal and liquid water (or oil), and it can change phase easily between the two. (We as show you this in the video below.) Because ferrofluids can change phases when a magnetic field is applied, you’ll find ferrofluids used as seals, lubricants, and many other engineering-related uses.


Here’s a video on toner cartridges and how to make your own homemade ferrofluid. It’s a bit longer than our usual video, but we thought you’d enjoy the extra content.


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Download Student Worksheet & Exercises


Engineering and scientists use ferrofluids to make a liquid seal in hard disks around the spinning disks to keep out dust and grit (hard drives must be kept exceptionally clean!). They do this by adding a layer of ferrofluid between the rotating shaft and magnets which surround the shaft.


You can also use ferrofluids to reduce friction, the way ice and water are used in ice skating rinks. If you coat a strong magnet with ferrofluid, you can get it to glide across a smooth surface like a hockey puck.


NASA uses ferrofluids in the flight instruments for spacecraft, also!


Each particle of ferrofluid is like a each grain or a micro-magnet, which not only interacts with magnetic fields, but also with light.


With loudspeakers, the large magnets that interacting with the coil often heat up. If we replace the magnet with ferrofluid (which is a liquid, remember!) it will actively conduct the heat away from the coil and cool it down because cold ferrofluid is more strongly attracted than hot, and thus the cooler fluid flows toward the coil, and the warmer fluid moves away from the coil.


Exercises


  1. Is the ferrofluid a solid or a liquid?
  2. Does the strength of a magnet matter?
  3. What would happen if the magnet went over the rim of the cup?
  4. Does the ferrofluid have a north and south pole?
  5. What happens if you bring a compass near the ferrofluid?
  6. Name three specific ways ferrofluid makes our lives easier. How might you use a ferrofluid if you were inventing something?

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Eddy currents defy gravity and let you float a magnet in midair. Think of eddy currents as brakes for magnets. Roller coasters use them to slow down fast-moving cars on tracks and in free-fall elevator-type rides.


Here’s what you need to do this activity:


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Find a thick piece of metal, like copper or aluminum to work with your neodymium magnets.


Materials:


  • aluminum block (the thicker the better, although you can try a cookie sheet)
  • neodymium disc magnets

When you have your parts, you can watch the video:




What’s going on? Here’s the basic idea: when a magnet moves near an object that conducts electricity (usually metal), it creates electric currents called eddy currents which start to flow in the conductor. These eddy currents create magnetic fields (electricity causes magnetism, remember?) in the opposite direction of the moving magnet, slowing an object down so it appears to float.


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