Balloon Rocket
✨ Let go of the balloon and it flies the whole length of the room along a string, like a tiny rocket.
🧰 You need
- a balloon
- about five metres of smooth string
- a drinking straw
- sticky tape
- two chairs
- a measuring tape
⚠️ Keep balloons away from babies and small children, who can choke on burst pieces.
👀 What you will see
The balloon shoots forwards while air rushes out of the back. It slows down as the air runs out and stops before the far chair if the string sags. Each run goes a slightly different distance, so three runs give a fairer picture.
🧪 Do it
- Thread the string through the straw.
- Tie the string between two chairs so it is high and pulled tight.
- Blow up the balloon and hold the neck closed without tying it.
- Tape the balloon to the straw so the neck points backwards along the string.
- Slide it to one end, count down and let go.
- Measure how far it travelled and run it twice more.
💡 Why it happens
When you let go, the stretched rubber squeezes air out of the neck in one direction, and the balloon moves in the opposite direction. Every push comes in a pair: the balloon pushes the air backwards and the air pushes the balloon forwards with an equal push. That forward push is called thrust. A real rocket does exactly the same thing, throwing hot gas out of its nozzle rather than cold air.
🔁 Now try this
Send the rocket again with the balloon only half filled, measure the distance, and compare it with the full balloon.
🤔 Think about it
There is no air outside a spacecraft to push against, so how does a rocket engine still work in space?
🧘 Ask the Acharya
“There is no air outside a spacecraft to push against, so how does a rocket engine still work in space?” — ask him and he will explain it from your own chapters.
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