- 4 plastic lids from soft-drink or water bottles
- A drill or rotary tool
- A straight straw
- Masking tape or sticky tape
- A 15 cm by 10 cm piece of thick corrugated (rippled) cardboard
- 2 bamboo skewers
- Plasticine or Blu Tack
- A bendable straw
- A balloon
- A rubber band
What to do
- The plastic lids will become the wheels of the car. Ask an adult to make a hole in each lid with a drill or rotary tool. The hole should be just big enough for a bamboo skewer to fit tightly.
- Cut the straight straw in half. Tape half of the straw at one end of the cardboard, across the shorter side. Tape the other half at the other end.
- Thread a bamboo skewer through each half-straw to make the car’s axles.
- Put the bamboo skewers through the wheels (plastic lids). You should have a wheel on each end of each skewer. Use plasticine or Blu Tack to hold the wheels in place if they keep falling off.
- Bend the bendable straw. Cut the long part so the two parts are the same length.
- Blow up the balloon and let the air out a couple of times to stretch the rubber.
- Place the neck of the balloon over one end of the bendable straw and use the rubber band to keep the balloon on.
- Place the car so it’s on its wheels. Tape the bendable straw along the length of the car so the balloon rests on the cardboard. The straw should poke over the end of the cardboard.
- Blow up the balloon by blowing through the straw. Pinch the balloon so the air doesn’t come back out.
- Place the car on a clean, smooth surface and let the balloon go!
Questions to ask
Can you make your car go faster or further using the same amount of air? Try changing the size of the wheels.
When you let go of the balloon, the air moves out of the straw. The air moves in one direction and the car moves in the opposite direction.
Sir Isaac Newton developed 3 laws of motion in 1665 – when he was only 23 years old. These laws changed how people explained movement. Newton’s laws describe how the forces acting on an object affect the object’s motion.
Your balloon-powered car is a good example of Newton’s third law of motion – ‘To every action there is an equal and opposite reaction’. This means that if object A pushes on object B, object B pushes back on object A with the same amount of force. For your balloon-powered car, the contracting balloon pushes the air in the balloon backwards. That means the air in the balloon is pushing the balloon forwards. The balloon is joined to the car, so the car rolls. The motion is nothing to do with pushing on the air behind the car. In fact, your balloon car is like a rocket and would even work in space!
Newton’s third law of motion happens all around us every day. But it can be hard to understand. If you lean against a wall it is easy to imagine that your shoulder is pushing, or exerting a force, on it. It’s harder to realise that the wall is pushing back on your shoulder with an equal amount of force.