🎈 Does more air make a balloon rocket go farther?

My hypothesis

If I change how big the balloon is blown up, then how far the balloon rocket travels along the string will ______, because ______.

🔊 You fill in the blanks. Think about what pushes the balloon forward, and how long that push can last. A guess is a good because: the test finds out.

Change, measure, keep the same

Scientists call the thing you change the independent variable and the thing you measure the dependent variable. The things you keep the same are the controls: if one of them changed too, you wouldn't know which change made the difference. Try each of the 3 levels 3 times.

What you need

• 🎈 A balloon: 1 long or round one, and a spare
• 🧵 String or yarn: as long as the room, 5 m or more, and 3 short pieces
• 🥤 Straws: 1
• 🩹 Masking tape, to mark lines
• 📏 A tape measure, or a long ruler
• ✂️ Kid scissors
• 🩹 Tape

Steps

1. Thread a straw onto the long string, and tie it tight between two chair backs across the room.🔊
2. Tie the three short strings into loops 30, 45 and 60 cm around.🔊
3. Grown-up: A grown-up blows up the balloon until it just fills the 30 cm loop, and pinches the neck shut.🔊
4. Tape the balloon under the straw, with its neck pointing back at the near chair.🔊
5. Slide it back to a masking tape start line, and let go of the neck.🔊
6. Measure how far the straw went from the start line, and write it down.🔊
7. Do it two more times with the balloon the same size.🔊
8. Grown-up: A grown-up blows it up to fill the 45 cm loop for three tries, then the 60 cm loop for three.🔊
9. Find the middle distance for each size and draw a line graph.🔊

2 steps are a grown-up's, marked above. Write each number down straight away, in the table below, so nothing is lost.

Your results table

From 4th grade, add the tries for each level and divide by how many there were: that's the mean, and it goes in the last column. Then draw a line graph, because the thing you change is a number that goes up.

Why it works

🔊 Air squeezed inside the stretched balloon rushes out of the neck, and as the air is pushed backward it pushes the balloon forward. More air means the push lasts longer, so the rocket usually goes farther. The straw rubs on the string and the air pushes back on the balloon, so twice the size seldom means twice the distance.

Going further (7th and up): Change a second thing: tilt the string uphill at three slopes, test the 45 cm balloon on each, and draw both tests on one graph.

Board layout

This project at your grade

From 4th grade up, the table gets a mean column. See every project for 2nd grade, or print a blank results table.

What a judge will ask

• What did you change, and what did you measure? I changed how big the balloon is blown up and measured how far the balloon rocket travels along the string, in cm.
• What did you keep the same, and why does that matter? I kept the same balloon every time and the same straw on the same string, pulled tight the same, so the only difference was how big the balloon is blown up.
• How many times did you test it? 3 times at each of my 3 levels.
• If you did it again, what would you change or test next? I'd tilt the string uphill at three slopes, test the 45 cm balloon on each, and draw both tests on one graph.

Make it yours

Keep this project on this device and Peabody counts down to your fair day, with a plan for each day. Nothing is sent anywhere.

Try next

• 🚀 Does a pointed nose make a straw rocket fly farther?3rd–7th grade · 1 day of testing · free🚗 How things move · ✂️ Paper, tape and toys
• 🎯 Does a longer arm make a catapult throw farther?3rd–8th grade · 1 day of testing · free🚗 How things move · ✂️ Paper, tape and toys