I'll bet you are pretty good at holding still. You might run during all of recess , but when the bell rings, you line up with the teacher. You might ride your bicycle, but when there's a stop sign, you stop. You might go to school and the grocery store and to your friend's house during the day, but at night, you lie down and go to sleep. Sigh. If only molecules were as well behaved as you.
In case you forgot . . . and I am sure you have not, the whole world is made of very little building blocks. Atoms are one of the smallest things we know about, and they come together to make all the different things you see in the world. Molecules
are atoms that are stuck together and they make up all the things we see around us. Two that you might know are water and salt. Even though a grain of salt that is sitting on your table may not look like it is doing much, scientists have some other ideas.
When I spill the salt; do I throw it over my left or right shoulder? I can never remember!
Have you ever felt like you were going to burst out of your skin? Have you ever felt like you could run all day and not even break a sweat? Energy
is what can make things change. It can come in all different shapes and sizes, from a ball bouncing to heat coming off something hot to running from here to Alaska. What? You do not want to run that far? You are not alone. Even though they have a lot of energy, molecules do not move very far either.
Look at this glass of water. It's holding still. No one has bumped it. There are no ripples. Look at this salt. It was dropped onto this plate, but now it's just sitting there. Very still. Neither the salt nor the water are moving. Or are they? Molecular motion
is the idea that molecules are always moving. This might seem confusing. How can they always be moving? They are only moving very, very short distances. Think of it this way. If molecules are in the form of a gas, it's like they're at a park and they fly all around, bumping into each other. If they are in the form of water, it's like they are in a busy hallway. They have to stay in a smaller area, but they can still move around. If they are a solid, like a table, then it's like they are in a classroom. They can still move a little in their chairs, but not that much.
Wait a minute, I just saw that table move. No, really!
So wait, if we cannot see these moving molecules and it looks like the salt and the water are holding still, why do we think they are moving? The Kinetic Theory of Matter
says that matter is made of molecules that never stop moving. Scientists came up with this idea because it would help explain a lot about why matter does what it does. Think about heat. In order for something to heat up, something hot has to touch it. The building blocks in the hot thing are very excited, moving all around. When they touch something cold, they will crash into those cold building blocks that are not moving very much and make them move. In order for heat to keep moving through everything in our world, the parts that make it up cannot stop moving.
When things get this hot, it's best not to touch them.
They never rest? Do they ever get tired? Can something become cold enough that it will stop moving? Absolute zero
is the idea that if something gets cold enough, the molecules will stop moving. We have never seen this happen before. It is only an idea. The problem is that, one way or another, everything touches something else in this world. You might not be touching that door, but you are touching the air that touches the air that touches that door. It's hard to keep parts that are moving around from moving something else. Nothing can get cold enough to stop its molecules from moving because the molecules are always touching something that's touching something that has moving molecules.
Even the cold at the North Pole is no where near absolute zero. If it was these polar bears would be frozen solid.
Molecules cannot sit still. They are flying around the air and splashing with the water. Even if they are in something like a table, they are still moving around a little. Even though we cannot see them move, we are pretty sure they are moving because heat has to move from one thing to another when molecules crash into each other. This makes it very hard for something to reach absolute zero, where it would not move at all. So the next time you have so much energy you feel like jumping out of your skin, remember that at least a part of you is moving all around.
School For Champions. "Kinetic Theory of Matter" School For Champions, 2011. <http://www.school-for-champions.com/science/matter_kinetic_theory.htm>