Demonstrate Newton's Third Law with a Balloon
Turn an ordinary balloon into a fast-moving rocket and watch action and reaction forces work together. This simple activity makes an important law of motion easy to see, test and remember.
Image: Samrudh Srinivas via Wikimedia Commons, licensed under CC BY-SA 4.0.
What will you discover?
Action force
Air rushes out of the open end of the balloon in one direction.
Reaction force
The balloon is pushed in the opposite direction and moves along the string.
Rocket connection
A rocket also throws gas backward, and the reaction force pushes the rocket forward.
Materials needed
One balloon
A long balloon works well, but a round balloon can also be used.
String
Use about 3 to 5 metres of smooth string or fishing line.
Drinking straw
A straight straw will guide the balloon along the string.
Adhesive tape
Two small pieces are enough to attach the balloon to the straw.
Two supports
Use chairs, door handles or other stable points at a similar height.
Measuring tape
Optional, but useful for comparing distance and travel time.
Stopwatch
Optional. A phone timer can help you measure each launch.
Helper
A partner can hold the balloon while you prepare the track.
Interactive balloon rocket simulator
Choose how much air is inside the balloon, inflate it and press launch. More stored air produces a stronger and longer push in this simplified model.
Step-by-step method
Prepare the guide
Pass the string through the drinking straw before tying the string to anything.
Make the track
Tie the string tightly between two stable supports. Keep it as straight and level as possible.
Move the straw
Slide the straw to one end of the string. This will be the launch position.
Inflate the balloon
Blow up the balloon but do not tie its opening. Pinch the opening so that air cannot escape.
Attach the balloon
Hold the balloon below the straw with its opening pointing away from the travel direction. Tape it to the straw.
Launch
Release the balloon opening. Observe the air moving backward and the balloon moving forward.
Why does the balloon move?
Inside the inflated balloon, stretched rubber pushes on the air. When the opening is released, the air escapes rapidly backward. The balloon pushes the air backward, while the air pushes the balloon forward with an equal force in the opposite direction.
Force on the air
The balloon pushes escaping air backward.
Force on the balloon
The escaping air pushes the balloon forward.
Turn it into a fair investigation
| What you change | What you measure | What you keep the same | Prediction |
|---|---|---|---|
| Amount of air in the balloon | Travel time or distance | Balloon type, string, straw and track length | More air may create a stronger or longer push. |
| Balloon size or shape | Travel time | Amount of air and track setup | Different shapes may change air flow and drag. |
| String angle | Travel time | Balloon and amount of air | A downward slope may help, while an upward slope may slow the rocket. |
Where else can you see this law?
Rocket launch
Hot gases move downward, while the rocket is pushed upward.
Swimming
A swimmer pushes water backward, and the water pushes the swimmer forward.
Jumping
Your feet push the ground downward, and the ground pushes your body upward.
Walking
Your foot pushes backward on the ground, and the ground pushes you forward.
Rowing a boat
The oar pushes water backward, and the water pushes the boat forward.
Releasing a balloon
Escaping air moves one way, while the untied balloon moves the other way.
Quick knowledge check
Which statement correctly describes the action and reaction in the balloon rocket?
Safety notes
Keep uninflated and burst balloon pieces away from babies and young children because they can be a choking hazard. Do not overinflate the balloon. Keep faces away from the balloon while inflating it. Ask an adult to help when cutting string or placing the track high above the floor.
Frequently asked questions
How does a balloon demonstrate Newton's Third Law?
The balloon pushes air backward through its opening. The escaping air pushes the balloon forward with an equal force in the opposite direction.
Why is a straw used in the experiment?
The straw slides along the string and keeps the balloon moving on a clear, controlled path.
Why must the string be tight?
A tight string reduces sagging and helps the straw move more smoothly. A loose string can increase friction and make the results less consistent.
Will more air always make the balloon faster?
More air can provide a stronger or longer push, but the result also depends on balloon shape, air leakage, friction, drag and how straight the track is.
Do action and reaction forces cancel each other?
No. They are equal and opposite, but they act on different objects. One acts on the escaping air and the other acts on the balloon.
Can this experiment be done without a straw?
You can release a balloon freely, but its path will be unpredictable. The straw and string make the motion easier to observe and compare.
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