 Now we've seen that heat is just a type of energy, it's the energy in the microscopic motions of vibrating atoms and in the chemical bonds between them. But can we turn more traditional forms of energy, like kinetic energy or electrical energy, into heat and vice versa? Well we can. Let's imagine for example someone diving into the sea. They start off at the top of the pier because they've got gravitational potential energy. As they jump off, they fall, the gravitational potential energy turns into kinetic energy, they're moving faster, then they splash into the water. And before long they're just bobbing up and down on the sea. So where did the energy go? Where did all that kinetic energy go? Energy is conserved, it can't just disappear. What's happened is, is as they dive in, the water swirls around them, splashes into the air. Those big swirling motions soon break down into small swirling motions, and the smaller and smaller, and it just ends up as jiggling atoms. And so the energy of their fall turns into the energy of swirling water, which turns into hot water. So principally if enough people jumped off enough piers into the sea, you could warp up the sea by a measurable amount. That would take an awful lot of people jumping in, because the sea has a very large heat capacity. Or consider dropping a pen. Once again, we've got to begin with the pen above the table, so it has gravitational potential energy. As it falls it turns into kinetic energy, but where does it go? Some of it goes into sound energy. The sound energy itself hits the walls and your eardrums and gets converted into heat there by making the atoms jiggle. Most of it however goes into warming up the pen and the table. As it hits it bends the table, it bends the pen, and those vibrations of the atoms break down once again into smaller and smaller vibrations, until it ends up with a slightly hotter pen, slightly hotter table, slightly hotter eardrums where you descend into the sound. How about the other way around? Can you turn heat into motion? Well, you can. The most famous example would be like an internal combustion engine. What you have is a cylinder with a piston, and you spray in fine droplets of petrol and set fire to them. So the chemical energy in the petrol turns into heat, and it makes the gas in the cylinder very hot, because the gas is very hot, has a very high pressure, and therefore it pushes down on the piston, and it's that pushing on the piston that makes your car work. Very similar thing happens in steam engines. It happens in power stations and gas turbines and so on. In all cases you're turning heat, which usually comes from chemical energy into motion. So you can go both ways. You can turn motion or electrical energy or something like that into heat, and you can go the other way around. You can turn heat into motion, and if you connect this motion to a dynamo, you can then turn it into electricity if you wanted to.