Pendulum Test: Heavy or Long?

What you need

• Painter's tape, 1 roll
• Paper bag, 1 small bag
• Phone, 1, for the 15 second timer
• Paper, 2 sheets
• Crayons or markers, pencils or markers
• String, 2 pieces, 40 cm and 20 cm
• Coins, about 20

How to do it

Grown-up prep: Choose a sturdy table with clear space below the edge. Use coins in a bag rather than keys for little hands, and stay close while the weight swings.

1. Put 10 coins in the small bag and tie it to the long string.
2. Tape the string to the table edge so the bag hangs freely.
3. Write your prediction: does weight or string length change the swing speed?
4. Pull the bag to the side, let go, and count swings for fifteen seconds.
5. Double the weight by adding 10 more coins, then test again.
6. Now halve the string length and test again, changing only that.
7. Record every count in a table and draw a bar chart.
8. Present your findings like a science fair, and compare with your prediction.
9. Now test more! What else could you change on your pendulum?

Play it again

• Length ladder: test four string lengths and line up the results from slowest to fastest.
• Mystery weight: a friend secretly changes the weight, and you work out whether it changed using only swing counts.
• Start height: keep everything else the same and test whether a bigger or smaller pull changes the swing rate.