The air in the box is made up of a lot of small “particles” called atoms and molecules. We try to imagine what these look like but they are so small that we can’t be totally sure. Usually we imagine an atom looks something like

The center is called the atom’s nucleus and the other things are called electrons. We also imagine a molecule looks something like

Where each of these little balls stuck together to form a molecule is actually an atom.

All of these little atoms and molecules are whizzing around very fast in the box and when they hit a wall or each other they bounce off very hard. Just like if you run at someone, hit them and bounce off each atom or molecule pushes whatever it hits. Each atom or molecule doesn’t hit very hard because they are so small but there are so many of them that all together they can push very hard against a wall. This push is called pressure and it is what makes a balloon get bigger when you blow it up.

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Tags: Physics, Science

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