Jet balloon

Follow these instructions to make your own jet balloon and learn how aeroplane jets work.

• 19 May 2006 | Updated 14 October 2011

• What you need
• What to do
• What's happening

What you need

To do this activity you will need

• a balloon (not blown up)
• a short piece of drinking straw
• a long piece of string
• sticky tape
• two friends.

What to do

Cartoon of the jet balloon experiment

1. Blow up the balloon and hold the neck to stop the air escaping.
2. Ask your friends to hold either end of your string so the string is taut.
3. Thread the straw onto the string and tape it to the balloon so that one end of the straw points to the neck of the balloon.
4. Hold the balloon at one end of the string and let go of it.

What's happening

The balloon should fly to the other end of the string as it deflates.

Many years ago, a scientist named Isaac Newton realised that when an object applies a force onto another object, the other object pushes back with an equal force in the opposite direction.

When you let go of the balloon, the air is pushed out of the neck of the balloon. As it does, the air pushes on the balloon with equal force in the opposite direction, so the balloon is pushed along the string. The air comes out of the balloon faster than the balloon is pushed along, because the air is much lighter than the balloon.

All rockets work by using the same principle. In a rocket, fuel is burned in a combustion chamber, which is open at one end. As the fuel burns, it produces hot gases, which rush out the open end of the chamber. Since the gases are being pushed in one direction by the rocket, the rocket is pushed in the opposite direction with equal force.

For more hands-on activities, join CSIRO's Double Helix Science Club.