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Physics Force and motion
Class 9 Intermediate About 15 min Free

Action and reaction: the balloon rocket

Launch a balloon rocket along a string. Change the amount of air, the nozzle and the load, and compare the action and reaction forces.

Core concept

When one object pushes on another, the second pushes back with an equal and opposite force

Topic: Force and motion

Newton's third law says that force: A push or a pull. Forces can start, stop or turn things. All key words always come in pairs: if object A pushes on object B, then B pushes on A with a force of the same size in the opposite direction. The two forces act on different objects. In a balloon rocket, the stretched balloon squeezes air out backwards (the action) and the air pushes the balloon forwards (the reaction). Rockets, jet engines and even swimming work in the same way.

Key words explained

What you will learn

  • State Newton's third law of motion.
  • Identify the action and reaction forces in a balloon rocket.
  • Explain how the amount of air and the load affect how far the rocket travels.

Before you start

  • Know that forces have a size and a direction.

Materials

  • Long balloons and a pump
  • Drinking straw, sticky tape and paper clips
  • 5 m of smooth string

Equipment

  • Two supports to hold the string tight
  • Measuring tape

Procedure

  1. Launch the balloon with 1 L, 2 L and 3 L of air and record how far it goes each time.
  2. Remove the paper clips and launch it again, then launch it with the 40 g load.
  3. Change to the wide nozzle and compare the forces and the distance.

How this simulation is simplified

  • The balloon, straw and tape have a mass of 20 g.
  • Each nozzle gives a steady push while the air escapes; friction on the string then slows the rocket at 2 m/s².
  • The string is 5 m long, so the rocket cannot go further than 5 m.
Bench