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Did you ever wonder what makes the wind blow? Or maybe how thunderstorms form? Both of the answers are really complex if you dig deep enough, but you can start with a basic understanding of something called convection. Convection is basically the way that fluids, things like air and water, move when parts of them have more heat than others. There’s a very important universal law that heat always moves to colder areas, and when this happens in fluids we get convection. All sorts of different weather affects can occur thanks to convection. Today’s activity is a way to visualize convection to see how heat can move and how it might affect the weather in your neighborhood.
Materials:
- Water (you’ll need lots!)
- A large clear Tupperware container (rectangles are best, and the longer the better)
- An ice cube tray
- A cup or glass
- Red and blue food coloring
Process:
- Fill your ice cube tray with water and add a drop or two of blue food coloring to each cube. When all of the water is nice and blue, pop it in the freezer.
- Wait. That stuff needs time to freeze.
- Check the freezer. Is it ice yet? Nope? Better put it back in, I guess.
- Wait some more.
- How long does it take for water to freeze? Jeez.
- Okay, it’s finally frozen. Whew. I was about to fall asleep. Take out your blue ice and set the tray aside for a moment.
- Fill your Tupperware container with water.
- Drop a few of your blue ice cubes into one of the short ends of your rectangular Tupperware. They’ll start to melt immediately. What happens to the cold, blue water as the ice cubes melt?
- Fill your cup or glass with hot water from the faucet and mix some red food coloring into it. Pour it into the opposite side of your Tupperware.
- Observe this system you’ve created. What is happening to the hot, red water? How is it moving differently from the cold, blue water? Do you see any convection?
- Bonus step: wait for a really long time, maybe go do something else, and then come back to your convection system. What color is it? How is it moving? Dip your finger in and test the temperature. What happened to it over a longer period of time?
Summary
If everything went to plan you should have seen the cold, blue water moving to the bottom of the Tupperware as the ice cubes melted while the hot, red water moved across the top. If you watched long enough you may have even seen some of the red water reach the ice cubes, mix with the blue water, and start to sink to the bottom. You just watched convection happen. You may have heard that heat rises, and it’s true in water just like it is in a hot air balloon. The red water was hot, so it stuck to the top, while the blue water moved along the bottom. But because heat likes to travel to places where there is less of it, your red water started moving towards the blue water on the opposite side. When it mixed with the blue water it cooled down, causing it to sink, and clearing the way for more red water to move into the place it had been before. While that’s happening, blue water is moving to fill in the places the red water used to be on the other side.
That’s cool and all, you may be thinking, and it makes the water look all swirly and pretty, but what does it have to do with wind and thunderstorms?
Well, imagine that you’re standing on the beach feeling a nice, cool sea breeze in the morning. Convection is happening here: the rising sun heats up the ground faster than it heats up the water. This makes the air above the ground heat up quickly as well, and since heat rises, the hot air starts to go up. Convection! This means that there’s more air pressure high up above the land than there is down close to it, since lots of air is moving in that direction. The air right above the water is colder, so it hasn’t started to rise yet, but suddenly there’s low air pressure right next to it on the land, and it moves in to fill up that air pressure void. You feel that moving air as wind.
But what about thunderstorms? Here’s where it gets even more complicated. Not only does a thunderstorm require warm air to start rising, the air also has to be humid, or have moisture in it. As it gets higher and higher the temperature begins to drop, which causes the moisture to condense out of the air, or form tiny water droplets. This is how clouds form. When water condenses out of the warm air, a little bit of extra heat, called latent heat, is released, which makes it keep rising, and more warm, moist air just keeps moving up under it and condensing, creating a bigger and bigger cloud. If this goes on long enough, the cloud can’t go up and higher and it starts to spread out into a wide, flat anvil shape, the classic shape of a thundercloud, or a cumulonimbus cloud. These clouds eventually dump their water onto the ground in the form of rain and they can also create lightning and thunder.
Of course, even that much information is still just scratching the surface, but it gives you a good place to start in your understanding of weather. And it all begins with convection.
Want more Saturday Science? See all of our at-home activities on the blog or Pinterest.
