Here's a clip from the BBC's Fun to Imagine series, in which Richard Feynman explains the amazing thing that happens when you stretch and release a rubber band. I'd always wondered why wide rubber bands got warm when you stretched them, and now I know! Feynman was a brilliant physicist and an even more brilliant physics-explainer, who busts out lines like "The world is a dynamic mess of jiggling things if you look at it right" (here's a transcript).
But these strings are being bombarded on the side by these other atoms trying to shorten them, by kicking them. So it pulls back – it’s trying to pull back, and this pulling back is only because of the heat. So if you heat a rubber band, it will pull more strongly. For instance, if you hang a weight on the rubber band and put a little match to it, it is kind of fun to watch it rise – the way it heats more, and there’s another thing you could check this idea is right – that it’s heat that drives the rubber band: if you pull the band out, just like you push the piston on the gas, if you pull the band out, these tightening string hitting the molecules makes them move faster, and so it is warmer. And if you take the band and let it in, then the molecules hitting the strings which sort of give as the thing hits, they they give in to the the soft like, and they lose energy when they hit this retiring band, straight string. So it cools. And there is a little way you could do this – you’re not very sensitive; it’s a small effect. If you take a fairly wide rubber band, and put it between your lips, and pull it out, you’ll certainly notice it’s hotter.
And then if you then hold it out and let in, you will notice that it is cooler; at least you will notice there’s a certain difference in what happens when you expand it and when you contract it. And that’s I’ve always found rubber band fascinating to think. When they’re sitting on an old package of paper for a long time, holding those papers together, it is done by a perpetual pounding pounding pounding, and the atoms that gets these chains to hold it, trying to keep them and [kink] keep them, year after year well, rubber bands don’t last that long, but, any how, for a long time, trying to hold this whole thing together.
The world is a dynamic mess of giggling things if you look at it right. And if you magnify, you will hardly see a little thing anymore, because everything is jiggling in its own pattern, and there’s a lot of little balls. It’s lucky that we have such a large scale of view of everything, that we can see these as things, without having worry about all these little atoms all the time.