Find out how you can knock down a tower of blocks without touching them.

For this experiment you'll need:

  • A plastic bottle
  • A carrier bag
  • A pair of scissors
  • A rubber band


  1. First cut the bottom off your bottle.
  2. Then pull the carrier bag over the bottom of the bottle.
  3. Secure the carrier bag with a rubber band.
  4. And there we go! What you've made is an air cannon!
  5. Just give the air cannon a thwack on the back and it will release a little spurt of air.
  6. Now lets knock down that tower!

Science behind the experiment

When the plastic bag is pushed into the interior of the drinks bottle, the volume decreases and pressure increases. The increase in pressure forces some of the air out of the hole.

The speed at which the air leaves the bottle depends upon the diameter of the hole, the smaller the hole the greater the speed of the air.

Key Terms:

  • Volume – is the quantity of three-dimensional space occupied by a liquid, solid or gas. Common units used to express volume include: litres, cubic meters, gallons, millilitres, teaspoons, and ounces.
  • Pressure – is the force per unit area. To increase the pressure you need to either increase the force or reduce the area the force acts on.

Activities and Questions

Try using bottles of different sizes, which shape and size creates more pressure?

Experiment with different objects. Weigh the object and find out when they are to heavy to knock over. Can you then adapt your cannon to overcome this?