Lesson 1 Grades 3–5

Push and go: balloon rockets

Timeabout 45 minutes
WorksheetE1 Balloon rocket
Rocket Builderoptional, on the projector at the end

On this page

Standards
I can…
Words to know
Materials
Steps
Check for understanding
Teacher notes

Standards

Code	In plain words
3-PS2-1	Test how even (balanced) and uneven (unbalanced) pushes change the way something moves.
3.MD.B.3 (math)	Show results on a bar graph.

Practice: planning and carrying out investigations. Crosscutting concept: cause and effect.

I can…

I can explain that a rocket pushes air or gas out the back, and the air pushes the rocket forward.
I can tell an even push (nothing changes) from an uneven push (it starts, stops, speeds up or turns).
I can run a fair test where I change only one thing.

Words to know

Force a push or a pull.
Balanced forces pushes that are even. Nothing changes.
Unbalanced forces pushes that are not even. Something starts moving, stops, speeds up or turns.
Thrust the push that moves a rocket forward.

Materials

For each group of 3–4:

2 long balloons (latex-free if anyone has an allergy)
4–5 m of string or fishing line, tied between two chairs
1 drinking straw, tape, a binder clip or clothespin (to hold the balloon shut)
A tape measure or metre stick
Worksheet E1 and a pencil

45 minutes · learn plan hands-on wrap up

1Hook5 min

Blow up a balloon, hold it up, and let it go without tying it. Ask: Which way did the air go? Which way did the balloon go?

2Learn10 min

Read aloud
When you let go of the balloon, the air rushed out the back. The air pushed back on the balloon, and the balloon zoomed forward. Every push has a push back. A real rocket does the same thing: it pushes hot gas out the back, and the gas pushes the rocket up. That push is called thrust.

Before you let go, your fingers held the balloon still. The pushes were even, or balanced, so nothing moved. When you let go, the push was uneven, or unbalanced, so the balloon moved.

3Do: balloon rockets on a string20 min

Balloon rocket on a string: the air rushes out the back, and the balloon zooms forward.

Setting up, step by step.

Thread the string through the straw. Tie the string tight between two chairs, at least 4 m apart.
Blow up a balloon a little (small). Hold the end shut with the clip. Tape the balloon to the straw, opening toward the start.
Pull the straw back to the start. Take off the clip. Measure how far it went. Do it 3 times.
Now blow the balloon up a lot (big). Do it 3 times again.
Circle the farthest try for each size on E1. Colour a bar for each one.

Fair test: only the amount of air changes. Same string, same straw, same balloon, same start line.

The setup. A string tied tight between two chairs · B straw on the string · C balloon · D tape · E clip holds the air in · F start line.

4Wrap up10 min

Talk about it:

Which balloon went farther? Why? (More air means a longer push.)
Where were the forces balanced? (Before letting go; at the very end, when it stopped.)
Where were they unbalanced? (While the air rushed out.)

Check for understanding

A balloon pushes air out the back. Which way does the balloon go?
A balloon is held still on the string. Are the forces balanced or unbalanced?
In our test, what was the one thing we changed?

Answer key

Forward: the opposite way to the air.
Balanced (nothing is changing).
The amount of air in the balloon.

Teacher notes

Set up before class: tie the strings, and pre-cut tape strips. Long balloons work best; round ones work too.
Grade 3: compare which balloon went farther; skip measuring if time is short. Grade 5: find the average of the 3 tries (add them and divide by 3).
What to expect: big balloons usually go farther. If every balloon reaches the end of the string, make the string longer.
Rocket Builder (optional, 3 minutes): on the projector, open the app in Beginner mode, build any rocket and press ▶ Watch it launch. Point out the flame at the bottom: hot gas going down, rocket going up, the same idea as the balloon.
Real rocket fact: a rocket does not push against the air or the ground. It pushes on its own gas, which is why rockets work in space.
Safety: nobody stands at the end of the string. Watch for latex allergies.
Projector tip: after Build my rocket, open the launch simulator in Simple mode (big buttons and text, made for a projector): press ▶ Watch it launch, or add &simple=1 to the launch page's address.