Here is the latest experiment in our ‘home science for kids’ series – how to make your own balloon-powered car.
**You will need an adult to help you to build this car**
An empty water bottle
Four plastic bottle caps (or you could use four tealights like we did)
A wooden skewer
Scissors and sticky tape (and a drill if available)
1. Cut the wooden skewer and one of the straws in half.
2. The water bottle will be the chassis of your car. Mark 4 dots onto your water bottle as shown below. Ask an adult to help you to make holes where these marks are that are large enough to push a straw through.
3. Push one of the cut straws through the two holes at the front of your car and the other one through the two holes at the back of your car. These make the axles for the wheels to fix on to.
4. Push one half of the wooden skewer through the front axle and one half of the wooden skewer through the back axle.
5. Get an adult to help you to make a hole in the middle of each of the four bottle caps, just large enough to fit the end of the skewer through. (They could use scissors but if they have a drill that would be easier).
6. Fit your bottle cap wheels onto your axles. (You could secure them with blue tac if they don’t hold on well enough).
7. Check that your car rolls nicely when pushed along a flat surface; make any necessary adjustments to it if it doesn’t.
8. Blow the balloon up a couple of times to make sure it is easy to do. Take the second straw and attach the neck of the balloon to it with sticky tape.
9. Make a hole in the top of your car and push the straw through and out of the open neck of the bottle (take off the cap). Tape it into place to hold it firm.
10. Blow through the straw to inflate your balloon and put your finger over the end of the straw to hold the air inside the balloon.
11. Put the car on a nice flat surface and take away your finger. What happens?
How can you make your car go further?
Try changing the amount of air you blow into the balloon.
Change the direction of the straw, can you make it more upright or make it more horizontal?
Try making your car from wood or cardboard and test out different designs.
Make your wheels from cardboard or wood, does this make it go faster or further?
Try making ramps to send your car up or down.
The science behind this experiment is all about energy.
When the balloon is inflated it stores the compressed air and stretched rubber as potential energy. When you let the air out of the balloon, the potential energy is converted into kinetic energy; this is the energy of motion, which is why the car moves. The more air in the balloon, the more kinetic energy and the faster or further your car will travel.
This experiment also demonstrates Newton’s Third Law of Motion. “For every action there is an equal and opposite reaction.’ The air pushes back on the balloon and this pushes the car forwards.