Density is basically how tightly packed atoms are. Mathematically, density is mass/volume. In other words, it is how heavy something is, divided by how much space it takes up. If you think about atoms as marbles (which we know they’re not from the last lessons but it’s a useful model), then something is more dense if its marbles are jammed close together.
For example, take a golf ball and a ping pong ball. Both are about the same size or, in other words, take up the same volume. However, one is much heavier, has more mass, than the other. The golf ball has its atoms much more closely packed together than the ping pong ball and as such the golf ball is denser.
This experiment builds on the Play With Your Food experiment, so we’ll be learning more about density. Are you ready?
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Gather your materials:
- small paper cups
- a scale that measures small masses (a kitchen scale is good)
- bunches of different small stuff (pennies, cereal, marbles, etc.)
- a little water and/or other liquids (milk, syrup, etc.)
- pencil, paper
- measuring cup (optional)
- container that’s larger and deeper then the small paper cup (optional)
1. Put a line with a pencil on the inside and on the outside of the paper cup about half an inch (centimeter) from the top.
2. Fill the cup to the line with whatever kind of stuff you’re using.
3. Weigh the cup and record its mass.
4. Empty the cup and fill it with something else. Record its mass as well.
5. Continue until you’ve done at least five different masses.
For advanced students:
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The following steps are optional. They will help you find out the volume of the materials you’re using. I recommend doing this only if the math won’t turn you off to the concept.
6. Take your larger container, fill it to the brim and place it into your bowl.
7. Take your paper cup and push it into the larger container. Push it in until it reaches the line on the outside of your cup. You should have water coming out of your glass and going into your bowl. Pull the paper cup out of the container and pull the container out of the bowl.
8. Take the water in the bowl and pour it into the measuring cup. Write down the measurement. This is the volume of the cup. Since you are using the same volume for each measurement, (you’re filling the cup to the same line each time) you only need to do this once.
9. Lastly, take your masses and divide each one by the volume. This will give you the density of each material.
So, there you go. Density is mass and volume. How heavy is it and how much space does it take up. If something has a great density, its atoms are very tightly packed together.
There’s a great story about Archimedes and density. The story goes that the king gave a crown maker a hunk of gold and the crown maker was supposed to make a crown using all the gold. Later the king got the crown but, being suspicious, wondered if the crown maker really used all the gold or if he cheated and kept some of it.
Supposedly the king was really bothered by this and felt he needed to find out. He went to Archimedes and asked him to find out if, indeed, he had been cheated or not. At the time, this was a very difficult question. Archimedes knew how heavy it should be if it was a certain volume, but only knew how to get the volume by multiplying length x width x height. How do you do that with an ornate crown? Needless to say the king was against smashing the crown into a cube!
The story goes that this problem possessed Archimedes and he spent so much time thinking about it that he rarely ate, rarely slept and never bathed! Supposedly, that behavior wasn’t that uncommon for him when he was tackling tough problems. Finally his servants, who could no longer stand it, dragged him kicking and screaming to the bath.
The story goes that Archimedes noticed, as he slipped into the bath, that the water rose around him. He discovered that the water he displaced was a way to measure his volume and lo and behold the same method could be used to measure the volume of the crown! Supposedly, he was so excited about this that he jumped out of the tub and ran through the streets stark naked yelling “Eureka! Eureka!” Which means “I found it! I found it!”. He used this method on the crown and to the king’s disappointment (and the crown maker’s too) the crown was indeed missing some gold.
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Thank you!
Yes mass is in grams or kg (kilograms). Ounces can be tricky since it’s a measure of volume and also mass. Fluid ounce is volume, and ounce is mass. Density is mass per unit volume, so kg per m3 is common. You can also have:
kilograms per liter (kg/L)
grams per milliliter (g/mL)
metric tons per cubic meter (t/m3)
kilograms per cubic decimetre (kg/dm3)
grams per cubic centimetre (g/cm3)
1 gram/cm3 = 1000 kg/m3
megagrams (metric tons) per cubic metre (Mg/m3)
pounds per cubic foot (lb/cu ft)
pounds per cubic yard (lb/cu yd)
pounds per US liquid gallon (lb/gal)
pounds per US bushel (lb/bu)
slugs per cubic foot
We just figured out the water should be in ml to “match” the grams of the mass. But, we’d still like to know the proper way to express units of density.
Thanks!
The mass would be in grams. When we measure the water, is this in ounces? What is the unit of measurement for density?
Thank you,
Lesa