Convection: The Movement of Heat

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When matter is heated, it becomes less dense

This is because an increase in heat, which can be imagined as the motion of particles, causes materials to expand by increasing their kinetic energy. We see this plainly when we freeze or boil water:

Phases of Matter (Important Tangent!)

Molecules (like anything in the universe) would prefer to be in the lowest energy state. Less heat slows the movement of molecules, although even molecules in solids move a little bit (by vibrating). With less kinetic energy, molecules assume an orderly arrangement. Order (the opposite of entropy) in molecules gives them an even lower, more desirable energy. As molecules gain more heat, they start to move and can no longer remain in an orderly structure. In the case of water, this causes melting. Even hotter, and the kinetic energy of molecules becomes greater than the energy keeping them associated. This is when a liquid becomes a gas.

It is plainly obvious to us that a gas is less dense than a liquid, and that a liquid is (usually) less dense than a solid. Unfortunately, the simplicity of this example is compromised by the fact that ice is less dense than water.

Anyways, heat makes matter less dense!

And here we can use the example of the less dense ice cube in a glass of more dense water to appreciate that less dense things float on top of more dense things!

And essentially, that is the exact point of this whole blog.

Hot fluids are less dense; they rise. Cold fluids are more dense; they sink. When these fluids move, the heat travels with them.

This, my friends, is Convection

But why do you care?

While this blog is not to help you prepare the perfect pastry, you really should still care about convection! I'm serious!

Lake Stratification

When the top of a lake heats up, it floats! The water that stays cold then sinks. When the top of the lake cools down in Autumn, it sinks back down and all of the water mixes. The water then stratifies (becomes layered) again when it freezes over, and mixes once more in the spring. This is a super important part of lake biology and can play a big part in drinking water treatment! Water in the top layer of the lake, the epilimnion, is often jam packed with Dissolved Oxygen (DO) which is essential for creatures of the lake. The bottom layer of the lake, the hypolimnion, has much less DO, and can even have such low DO concentrations that it is considered to be hypolimnetically anoxic. When a lake develops hypolimnetic anoxia, nutrients from the sediment may be released in the hypolimnion. When all the water in the lake mixes in Fall or Spring, these nutrients can make their way to the top and lead to some nasty business:

Algal Blooms Let's hope it never gets this bad in your local swimming hole!

So that's some nasty stuff, and I guess its a bit of a skip away from Convection

Convection also plays a huge role in winds!

"What's that, John?"
"Wind, Ringo!"

The movement of air all around our beautiful planet is caused by this convection phenomenon.

You may have been able to gather that from the picture at the very top of this post.

Convection shapes our air into cells, called Hadley Cells, which encompass the Earth. They are the cause of the Easterly tradewinds (which blow towards the west along the equator) as well as the Subpolar Jetstream (which causes your return flight from Europe to America to take longer).

Hey, if you're still reading, I gotta say thanks.

It means a lot when I know someone actually spends a little time checking these out.

Yes, there was no bigger kicker to this blog post; in the end it is just a post that gives a decent description of how convection works with maybe a little bit too much background on phases of matter. I just figure that the more you know about physics, the better able to understand science you will be. I hope this has been informative and that maybe the little section on lake stratification will help you decide not to use fertilizers with phosphorus on your lakehouse lawn.

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Til next time, cowboy

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Soreses:

Convection
Phases
Lake
Ringo