This experiment demonstrates how a build up in pressure can launch a rocket.
As we pump air through the water the pressure inside the bottle builds up until the force of the air pushing on the water is enough to push the cork out of the end of the bottle. The water rushes out of the bottle in one direction whilst the bottle pushes back in the other. This results in the bottle shooting upwards.
What you need
- an empty plastic bottle
- cardboard made into a cone and 4 fins
- a cork
- a pump with a needle adaptor
- Push the needle adaptor of the pump through the cork, it needs to go all the way through so you might have to trim the cork a little bit.
- Decorate the bottle with the cone and fins.
- Fill the bottle one quarter full of water and push the cork in tightly.
- Take the bottle outside and connect the pump to the needle adaptor. Ours wouldn’t stand up on the fins so we rested it on a table, but if you make some strong fins it should stand up by itself.
- Pump air into the bottle, making sure all spectators stand back, the bottle will lift off with force after a few seconds.
Please make sure an adult is around as the rocket takes off very suddenly and forcefully as you can see in this video clip. Do not approach the rocket once you have started pumping even if it looks like nothing is happening.
The Science bit
Space rockets work in a similar way to the bottle, but instead of squirting water they burn fuel to make a powerful jet of hot gas. The force of the gas downwards pushes the rocket upwards.
Isaac Newton worked out the three laws of motion which describe how all objects move. The third law says:
‘for every action there is an equal and opposite reaction’
This is demonstrated by the bottle rocket.