Balloon Car Lab

Explain propulsion with escaping air

Help your child connect backward-moving air with the forward push on the car.

🎈

Every control changes the car you can see.Balloon size, nozzle, body mass and wheel size all update before you test.

Nallo’s guide for parents

Before the first test

The setup is ready. Ask your child what they expect, then start the test.

Steps

Ask your child: “Which way will the air move, and which way will the car move?”
Start the prepared test after discussing your predictions.
Compare how strongly the car starts and how quickly the balloon empties.

2.2 L balloon · 8 mm nozzlebalanced push

Build the car, predict, then race.Simplified pressure-flow + rolling motion model

Make a guess

My distance guess

0.5 m

Discuss the observation

Ask your child what changed and what stayed the same.

READYHow far will your car go?

Run the starter once, then change exactly one visible part.

Show the numbers

Distance—your guess: 0.5 m

Top speed—modeled

Push time—until balloon empties

Start thrust—simplified estimate

WHAT TO TRYRace this design first.

Then make the nozzle much smaller or larger and compare the whole run.

A closer look at this test

💡What this run can teach

A balloon car is a trade-off: thrust helps acceleration, but the same air has to last long enough to keep pushing.

Try changing only the nozzle after your first run.

Why does the car move?

Air rushes backward out of the balloon. The air pushes the car forward in the opposite direction.

Try it: make the nozzle smaller and compare how far the same balloon takes the car.

An explanation to share

How you can explain it

Air shoots backward out of the balloon and pushes the car forward. A wide opening can give a stronger push, but the air runs out sooner. Rubbing at the wheels also slows the car.

NozzleThe opening where air leaves the balloon.

Away from the screen

An activity for you to guide

Prepare a straw on a taut string for your child to observe.
Tape an inflated balloon to the straw while holding the balloon opening shut.
Let go and watch. Keep uninflated balloons and broken pieces away from young children.

Explanation guide for parents

Stay with your child throughout the experiment. Read the task together, compare your predictions and start the test. Operate the controls, then discuss what changed.

Support your child’s reasoning

Ask children to point in both directions: air backward, car forward. Compare opening sizes with the same amount of air. Real balloon activities need close adult help, especially around younger children.

Ask: “What did you change? What did you notice? What will you try next?” A different result is a clue, not a bad score.

Screen and real life

Real balloons do not all stretch the same way. Air leaks and wobbly wheels can make a big difference.

Use the simulation to discuss patterns. You remain responsible for choosing and supervising any physical activity; real results can differ.

A question to take it further

Why might a strong, short push travel less far than a gentler, longer push?

A common misunderstanding

A stronger initial push does not always mean a longer journey. A larger opening can use the air sooner.

How the model works

Balloon pressure is simplified and falls as air leaves. Thrust is estimated from pressure and nozzle area; rolling resistance, axle torque and air drag oppose motion. Wheel radius changes axle force and wheel mass changes rotational inertia. Real balloons, leaks, wheel wobble and nozzle shape add variation.

Quick guide: s = seconds · m = metres · cm = centimetres · g = grams · kg = kilograms.

BUILD 20 · PARENT GUIDE · 29 SEP 2026