Balloon Car

A balloon, a straw and four wheels. Choose the balloon size, car mass and straw, then let go and see how far your car goes.

Straw
Floor
Thrust
0.170 N
Air left
100 %
Speed
0.00 m/s
Distance
0.00 m
Time
0.0 s
Acceleration
1.73 m/s²

The maths, live

Thrust F = 2 × ΔP × AF = 2 × 3000 Pa × 0.0000283 m² = 0.170 N
3rd law air on car = car on air0.170 N forwards = 0.170 N backwards
Friction f = μ × m × gf = 0.04 × 0.08 × 9.81 = 0.031 N
2nd law a = (F − f − drag) ÷ ma = (0.170 − 0.031 − 0.000) ÷ 0.08 = 1.73 m/s²

Try a wide straw and then a thin one with the same balloon. Which one goes further, and why?

How it works

The stretched balloon squeezes the air inside it and pushes it backwards out of the straw. Newton's third law says forces come in pairs: if the car pushes the air backwards, the air pushes the car forwards just as hard. That forward push is called thrust.

The car only speeds up while the thrust is bigger than friction and air resistance. A wide straw lets the air out fast, giving lots of thrust for a short time. A thin straw gives a gentle push that lasts longer. When the balloon is empty, friction slowly brings the car to a stop.

Try this

  1. Try every straw with a 3 litre balloon. Which one makes the car go furthest?
  2. Find the heaviest car that still moves on carpet with a thin straw.
  3. Double the balloon size. Does the car go twice as far?