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Air Cannon

An image showing an air cannon made from a coffee cup with a hole in the base and a balloon over the top

Use pressure in an activity you can get a real blast from!

Australian Curriculum links

  • Science > Chemical Sciences > Year 5 > ACSSU077
  • Science > Physical Sciences > Year 4 > ACSSU076
  • Science > Physical Sciences > Year 7 > ACSSU117

You’ll need

  • A paper coffee cup (corrugated or reinforced cups work best)
  • A balloon
  • Scissors
  • Masking tape
  • Candle & matches (optional)
  • Torn up paper or confetti (optional)

What to do

  1. Cut off the top of the round part of the balloon and keep the section with the neck. Tie off the neck of the balloon.
  2. Stretch the open end of the balloon over the top of the cup, being careful not to squish the cup. Try and align the neck of the balloon with the middle of the cup. You may need to fasten with masking tape.
  3. With your pen, poke a hole about 1cm in diameter in the middle of the bottom of the cup. You have now built your air cannon.
  4. Pull the balloon neck backwards then let it go suddenly so air shoots out of the hole at the bottom of the cup. Test that the air is coming out by having a friend place their hand in front of your air cannon.
  5. You can see the effects of the air cannon by shooting it at some torn up paper or the flame of a lit candle.

What’s happening?

Gases move from high pressure to low pressure. Drawing the balloon back lowers the pressure inside the cylinder, so air rushes in. Releasing the balloon increases the pressure inside the cylinder, so air rushes out, through the small exit hole. That’s where things get a bit more complicated.

The air starts spinning, rather than travelling in a straight line, for a number of reasons. These include friction between the air and the hole in the cup, as well the air outside the cup that resists moving away. The spinning air makes a toroidal vortex, which is a donut-shape of spinning air.

Real world links

Vortices form when fluids flow. You usually only notice them when you can see particles moving in the fluid, or have different coloured fluids mixing. Famous examples of these are smoke rings, which can be blown by volcanos and pirate’s cannons. Toroidal vortices can also be created underwater and are created by dolphins, who “play” with these underwater rings.

Scientists have recently used toroidal vortices to help explain how some waves behave strangely, as well as how they could help develop more efficient underwater travel.