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How do you get around the scorching problem when heating chili? I use a two-pronged approach. First, I set the heat on low, so that the chili doesn't scorch too quickly. Second, I stir it frequently. Stirring it takes some of the hot chili from the bottom and mixes it up into the rest of the chili. The result is that, instead of having a little hot chili and a lot of chilly chili, I have a pot of all-medium chili. A few minutes later, I stir it again, and I have an entire pot of slightly hotter chili.
This is called mechanical mixing. If I just left the pot alone, the chili wouldn't mix by itself. I have to supply the turbulence myself to force it to mix.
It's a lot simpler to heat up a pot of water. As the bottom of the water heats up, convection currents develop which carry the hot water from the bottom to the top. This happens because hot water is lighter (less dense) than cold water. By the same token, hot chili is lighter than cold chili, but the difference in density is not large enough to overcome the fact that chili is so thick that it strongly resists any movement.
The redistribution of heat within the pot of water is called convective mixing. Even though I leave the pot alone, the water mixes itself, because the temperature variations generate their own turbulence. Without the mixing, the top part of the water would take a long time to heat up.
A word of warning: it's easy to confuse the words conduction and convection. The way to keep them straight is to remember that thunderstorms, which involve violent mixing of air, are often referred to as convection. And when you think of conduction, you might think of a wire (a solid object) conducting electricity. For heat transport, solids tend to be efficient at conducting heat, but because they are solid, they can't transport heat by convection at all.
So, of the following three transport methods, which do you think would be the least important for heating and cooling the atmosphere?
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