Hey! Did you know that wind and air currents aren’t the same thing? Do your students know that? If the answer to either of those questions, but especially the second one, is “no”, then you’re in luck, Slappy! This Demo Science experiment will help you explain the difference in a fun and only moderately messy way. Huzzah!
The Ol’ Powdered Lamp Routine
This one requires but two pieces of equipment (equipments?) that you very well may already have in your classroom: a table lamp with the lampshade removed, and a canister of talcum powder. For starters, with the overhead lights on but the lamp off, hold the canister of talcum powder over the lamp and squeeze out a puff of the stuff. What happens? Jimmy Jack Nothin’, that’s what!
Then, turn the lamp on and give it a few minutes to warm up. While you’re waiting, regale students with the story of the time you and your cousin Pete shaved an entire cow on a dare. If you don’t have that particular Cousin Pete story in your pocket, just make something up. They’re kids, they’re not gonna know the difference. Lil’ dummies.
Anyway, once the lightbulb is nice and hot (speaking of, if you can still find an old-school incandescent bulb anywhere, install that in the lamp prior to this demo—those bulbs get way hotter than the twisty CFL bulbs do) turn the overhead lights off and repeat the talcum squeezin’ process.
What happens this time? Jimmy Jack Somethin’, that’s what!
See the Light Physics
If you did it right, the powder will rise up over the hot lightbulb. The bulb is, of course, producing heat, which causes the air above it to rise and carry the powder with it. The process in which warmer air pushes upward—due to its lighter density, which is, in turn, due to the heat—through cold air is called convection.
With the unlit, cold lamp, the talc just floated down through the colder, denser air surrounding the lamp. But when the heated air around the lit bulb rose, the cooler air around it flows into the void to take its place. The resulting vertical air movement is, in fact, and air current. Horizontal air movement—which is the same thing but sideways—is wind.
Wind and air current speeds are directly affected by the temperature difference between adjacent masses of air. Wind direction is affected by the location of these masses in relation to each other.
For an even better version of this Demo Science science demo, repeat the experiment in a room with little to no air flow. Your classroom almost certainly has the HVAC running right now–whether heating or A/C–or at least the windows open, any of which will affect the air currents in the demo. If you can’t find any rooms in your school that will work, perhaps you can convince the superintendent to spring for a modular cleanroom in which to perform this and other experiments. It’s probably not the worst use the school could put money to. The football team does not need new uniforms again.
Anyway, BOOM. #scienced