Can you hit the target with your air cannon?
Want to reach out and touch something with a puff of air? This tiny air cannon shoots vortexes of air that can be felt from metres away!
Safety: This activity uses a sharp scalpel or craft knife. You will need an adult’s help.
It’s surprisingly difficult to make a gust of air. Without an air cannon, flicking your finger will only push air a centimetre or two. Blowing as hard as we could, we couldn’t move a feather two metres away with just our lungs. So why does this air cannon work so well?
The first step is amplification. Your fingertip is small and doesn’t push much air. When you tap the plastic, you’re suddenly pushing a much larger area, and that means you’re pushing much more air.
A pulse of air escapes the cup, all through the hole. Since the hole is smaller than the plastic, the air speeds up to get out – so you get a pulse of air that’s bigger and faster!
But there’s one more trick to this device. As the short, sharp pulse of air leaves the cup, it sets up a donut-shaped air current called a vortex ring. This air shape is very stable.
Larger examples of vortex rings can travel many metres before they dissipate. Exactly how they work is very complicated, and not fully understood.
Some species of dolphin blow bubble vortex rings and play with them. Even some volcanoes have been spotted blowing rings filled with smoke or steam!
If you’re after more science activities for kids, subscribe to Double Helix magazine!
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