Science / All lessons / Forces and Motion

Balloon Rockets

Change one thing. Measure the result.

Lesson 17 of 41

Try this first

Before we start

Today’s story

A balloon let go zips around the room with a rude noise. Air escapes one way and the balloon goes the other.

The balloon pushes air out. The air pushes back on the balloon. That push is a force. Because the other forces are small, the balloon speeds up.

Rockets work the same way. Today you change one thing and measure.

See it

Hands on

30 minutes · Do this with a grown-up nearby

Thread the string through the straw and tie it across a room at a slight height.
Blow up a small balloon and pinch it shut.
Tape the balloon to the straw and slide it to one end.
Release the balloon and measure how far it travels.
Repeat three times.
Do the same with a large balloon.

Write or draw: A table with balloon size, three distances and the average.

Watch for: Did the larger balloon go farther? Was the string straight and tight?

Safety: Keep balloons away from faces when releasing and pick up popped pieces.

Same every time

Rule 1Change one thing

Only one change per test.

Rule 2Measure the same way

Same string, same start.

Rule 3Compare results

Look for the pattern.

Grandpa Fenn’s notebook

thrust
A push that moves an object forward.

force
A push or a pull.

variable
A thing you change in a test.

rocket
A device pushed forward by gas pushed out the back.

Poppy’s quiz

Tap an answer. Green means right. You will see why.

Talk about it

Did you know

Real rockets carry fuel that burns and shoots gas out the back to move forward.

Someone who does this

An aerospace engineer designs rocket engines and tests how they push.