A science and math blowout

A simple activity involving candles and the shape of air

A few months ago, I told my students that I could blow out birthday candles from across the classroom. They didn't believe me, of course, and I can't say I blame them. After all, some people have trouble blowing out birthday candles that are only a foot away. I did it, though. What's more, I was able to turn it into a fun activity that involved both science and math. You can do it, too. Here's how you go about it:

Cut an eight-inch hole out of the bottom of a garbage can. Cover the top of the can with a piece of heavy vinyl material like NaugahydeTM. Fasten the vinyl to the can with duct tape and bungee cord. (Use extreme caution when working with the bungee cord; it can cause serious injury if handled carelessly.)

When you hit the vinyl cover with your hand, out will come a great blast of air, which will easily blow out the candles. It's as simple as that.

Question time. Since your students will undoubtedly be impressed, you may want to stop right there. There's nothing like leaving in a blaze of glory. Resist the temptation, however, and start asking questions.

First, ask your students for their thoughts on how the air was forced out of the garbage can. Then ask them what shape the air was when it traveled out of the can. A ball? A cylinder? No shape at all?

Change of scenery. The next part of the activity - observing the shape of the air must take place in the great outdoors.

Take the can outside, put a smoke bomb in it and hit the vinyl cover.

Your students will be amazed at the shape of the smoke (doughnut-shaped) and at the way the smoke spirals outward (counter-clockwise if you're north of the Equator).

You can continue by experimenting with triangular and square holes. You'll find, as I did, that the shape of the air is roughly the shape of the hole as it leaves the garbage can, but it soon becomes doughnut-shaped.

Where does the math come in? Well, you can have your students explore the volume of the can and the areas of round, triangular and square holes. We even built a rectangular-shaped "wind machine" that equalled the volume of the can. You may not want to go that far, of course, but no matter where you stop, you'll prove to your kids that learning science and math can be fun.

John Cowens teaches fifth grade at Fort Vannoy Elementary School, Grants Pass, OR.

Copyright Early Years, Inc. Jan 1997
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