Air is all around us, all the time (except underwater), and it’s always moving. Often, it’s too gentle for us to notice; other times, it can just about knock you off your feet. Horizontal air movement is, of course, wind, while vertical air movement creates an air current. We can “see” wind by the way it moves tree leaves, flying flags, and random debris. Visualizing air currents can be tougher, though these movements are just as important as wind to our weather.
With this handy dandy Demo Science science demo, you can explain what causes air currents and create a neat visual to go along with it. Who’s ready to science?
Powdered Donuts Lightbulbs Make Me Go Nuts
All you’ll need is a freestanding lamp with the lampshade removed, and a little bit of talcum powder. Six pounds or so should be just about right. This experiment will work better with an old-timey incandescent bulb instead of a modern compact fluorescent or LED bulb, so see if you can dig out one of those old dinosaurs from somewhere.
Start with the lamp turned off—it’s best to make sure it’s been off for a while, so it’s cooled completely. Leave the lamp off, sprinkle a light dusting of talcum powder over it from about a foot above, and see what happens. SPOILER
Clear the powder off the bulb and the surrounding fixture, then turn the lamp on. Give it a few minutes to warm up, then sprinkle it with talcum powder as before. What happens now? SPOILER ALERT: something will actually happen this time.
If all goes as planned, some of the powder will float in the air above the lamp, buoyed by the heat the light bulb produces. That heat, um, heats the air around the bulb, making it less dense and allow it to rise above colder, denser air that is not warmed by the lamp. Heated air becomes less dense because, when heated, its molecules (like those of nearly any substance) “expand” and move farther away from each other.
The process of warm air rising above colder air is called convection. Hot air goes up, cold air sinks into the formerly occupied space. The cold air, now closer to the heat source, will be heated and the whole process will repeat ad infinitum.
The greater the temperature difference between the cold and hot air, the greater the speed of the ensuing air current will be. Same goes for wind, but sideways. The direction in which wind blows depends on the relative location of hot and cold air masses.