🎯 Does a longer arm make a catapult throw farther?

My hypothesis

If I change how long the catapult's throwing arm is, then how far the paper ball flies will ______, because ______.

🔊 You fill in the blanks. Think about how fast the end of a long arm moves compared with a short one when they swing together. 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

• 🪵 Craft sticks: 8
• ➰ Rubber bands: 4
• 🧢 A bottle cap
• 📄 Paper: a scrap, scrunched into one ball
• 🩹 Masking tape, to mark lines
• 📏 A tape measure, or a long ruler
• 🩹 Tape
• 📏 A ruler

Steps

1. Build the craft-stick catapult from the Workshop, but leave the cap off for now.🔊
2. Tape the cap to the very end of the top stick: that's the normal arm.🔊
3. Stand the catapult on the floor with its back edge on a masking tape line.🔊
4. Put the paper ball in the cap, press the arm all the way down, and let go.🔊
5. Aim across the room, never at anyone, and measure to where the ball first lands.🔊
6. Write it down, then launch two more times.🔊
7. Tape a second stick along the arm so it sticks out 3 cm farther, and move the cap to its end.🔊
8. Launch three times, then slide the second stick out to 6 cm and launch three more.🔊
9. Find the mean for each arm and draw a line graph.🔊

Every step is one you can do yourself, with a grown-up nearby. 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

🔊 The bent sticks and stretched bands store energy, and when you let go they swing the arm up. Every part of the arm turns together, so the end of a longer arm travels farther in the same moment and moves faster. A faster ball usually flies farther, but the extra stick adds weight the bands must swing, so the gain can shrink.

Going further (7th and up): Change a second thing: launch the paper ball and a heavier ball of foil from each arm, and draw a line for each.

Board layout

This project at your grade

From 4th grade up, the table gets a mean column. See every project for 3rd grade, or print a blank results table.

What a judge will ask

• What did you change, and what did you measure? I changed how long the catapult's throwing arm is and measured how far the paper ball flies, in cm.
• What did you keep the same, and why does that matter? I kept the same paper ball and pressing the arm all the way down every time the same, so the only difference was how long the catapult's throwing arm is.
• 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 launch the paper ball and a heavier ball of foil from each arm, and draw a line for each.

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 higher start make a marble roll faster?3rd–8th grade · 1 day of testing · free🚗 How things move · ✂️ Paper, tape and toys
• 🚀 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

🔨 From the Workshop: this project grows from a Workshop build, with picture steps of its own.