 So we've talked about conduction, which is the main way that heat goes through a solid. In principle, you can get conduction inside a liquid or a gas, but in practice, convection is the main way, a different way, that heat goes around inside a fluid. How does convection work? Well, let's imagine we have a hot object over here immersed in some fluid, like air. It will heat up the air next to it. The air next to it, because it heats up, becomes less dense, and because it's less dense, it rises, hot air rises, so it'll flow up. And it might eventually cool down and come back down again, forming a convection cell, especially if there's a cold object over here, there's a cold object over there, the air near it will get cold and therefore become dense and will tend to fall. And so before long, very long, you're getting a cycle of air moving from the cold, from the hot to the cold, back and forth transporting heat. And that's what convection is. Let me show you a simulation of this. This simulation is using the Energy2D program. And what I've got here is a simulated room. And down here is a plate on the floor that I'm going to heat up. And we'll see what happens to the air. So let's run the simulation. So you see a plume of hot air rising. Before long what you can see is the heat is moving all the way around the room spreading out, cold air coming down, or the complicated it is in the middle. And this is indeed, generally speaking, how heaters will heat your room, whether you've got ducted gas heating or a radiator or something like that. It will generate heat, that heat will contact with the air near it and move all the way around. This is also how heat tends to flow through the oceans and tends to flow through the atmosphere. So it's a very common way for heat to move inside fluids. And in fact it's generally much faster than conduction in a solid. So generally speaking, if you want to get heat from one side of the room to another, you could put in some big metal pipes and let the heat conduct through it. But just heating up the air, letting the air flow around will generally transport it much faster.