If there is a force pushing in one direction, there is an equal force pushing in the opposite direction.
This is what Isaac Newton said around 300 years ago. The rocket age is very modern, but the science which explains how rockets work was understood hundreds of years ago. Rockets burn in a fuel chamber shaped like a bottle with a neck pointing down. The burning fuel produces large amounts of gases expanded by heat. The gases are forced down through the neck at high speed, forcing the rocket up in the opposite direction.
This fun activity explores this scientific principle using plastic bottles to make water rockets. Choose a large open area outside for this activity.
You will need
- plastic PET bottle
- bicycle pump
- rubber stopper to firmly fit inside the neck of the bottle
- inflating nozzle like those used for inflating basketballs
- cardboard carton with hole to support neck of bottle
What to do
With an adult to help, drill a hole in the rubber stopper to fit the inflating nozzle. Attach the nozzle to the pump. Fit the stopper and nozzle firmly into the neck of the bottle. Place the bottle upside down on the cardboard carton - your launch pad! Pump air into the bottle until the air pressure inside forces the stopper out of the bottom. What happens to the bottle?
Try it again, but this time put some water into the bottle before fitting the stopper. Pump air into the bottle until the air pressure forces the stopper out of the bottom. This time, water and air are forced down through the neck. This causes a force pushing the bottle up. How high did the water rocket go?
Try different amounts of water. What is the best amount of water to make the rocket go high?
Design fins for your water rocket. Do they improve the flight of the rocket?
CAUTION: Do not make any point at the top of the rocket — this could be dangerous.
From: Fun 'n' Science Activity Book, published by Questacon – The National Science and Technology Centre.