Getting Hot

If you were a vulture flying for the first time across certain parts of the desert, you would notice the waves. Not cool wet ones, but yellow, lumbering ones spread out across the land. The jagged, up-and-down ones made by the slow-moving winds, and long travel-lines by the faster ones. The well-known dunes shaped like the edge of a fingernail, in places where the ground is stiffer. And the spectacular, unmoving star-dunes made by colliding winds blowing from all directions.

Then, if you fly down and look closely at the waves, you will find they are actually made of many small, tiny particles called “grains of sand”.

If you were an albatross, looking down as you flew across the ocean from home to home, you would notice the waves. Not so much in the middle of the sea, but at the edges, near the land, at places where it had something to bump into. Near the middle, it’s more common to find swirling or running currents of water, but usually under the surface of the ocean. Sometimes great movements can be brought on by a strong wind or an earthquake, but in that case you should fly on fast and not bother looking down.

If you could look closely at the waves, very closely, through a very strong microscope, you would find they are actually made of many small, tiny particles called “molecules of water”.

If you were a puffin, travelling the sea on a ship of ice, you would be standing on the same kind of water molecule. Unless, of course, you were not standing but sitting. The difference is that the molecules of your iceberg would have much less energy than the molecules of the ocean waves. So they would be sitting quietly together in one solid block, without moving around. As your iceberg drifted to warmer lands, or lands where molecules have more energy (which is the same thing), the iceberg’s molecules too would become restless and start fidgeting. At last, they would be fidgeting so much that they wouldn’t be able to sit together any longer, and would start wandering about in liquid ways. Thats when your ship would become less iceberg and more water.

Why would going to warmer areas make your molecules more restless? That’s because “being warmer” actually means “having molecules which are more energetic and move around faster”. When you touch something and it feels hot, what you’re feeling is actually millions of molecules bumping into your skin. Unless of course you feel it with your teeth, because your teeth don’t have any skin. Now, to get back to the question, imagine you’re a molecule. A quiet one, which isn’t moving around much. And then, suddenly, one of the fast-moving molecules of the “warm” area comes and bumps into you. What do you do? You get pushed, and you start moving, too! Now you’re as much part of the “warmth” as the rest.

Of course, when that molecule bumped into you, it would have also slowed down a bit, because some of the movement-energy got transferred to you. That’s why water gets colder when you put ice into it, and ice gets warmer when you put water onto it.

If something disturbs the ants in an ant-line, the ants start moving a bit faster, and get a bit more spread out. That’s because whenever an ant is going to bump into another ant, they both quickly change direction. When they are moving faster, they almost-bump more often, so the change direction more often, so there are more times when the direction points outwards to where the ants hadn’t been before.

When the ants get very disturbed, they move around so fast that they spread out all over the place. That’s the same thing that happens to water-molecules, when they begin moving so fast that they turn into steam. Actually, this doesn’t happen just with water-molecules, but with any kind of molecule (and many kinds of ant). The difference is in how much energy they need, or how hard the have to be bumped, to move fast (like in stead) or slower (like in liquid water) or almost not at all (like in solid ice). Some molecules are heavier than others, and need harder bumps to get moving. So when we speak of things “melting” or “evaporating” or “freezing”, we really just mean that the molecules are changing their speeds.

There’s also something called “burning”. That’s when there’s so much energy to go around that completely different things start happening. Some of the molecules break apart, and the bits go and join onto other bits. But then they’re not the same molecules any more.

This article was originally published in Sirius #241, 19 Mar — 1 Apr 2017 “The Pokémon Maker”.