Make a Compound Pendulum

Build your pendulum with pennies, string, and plastic bags or film canisters and see what happens!

What you will need:

  • Two 35mm film canisters (and a couple spares) or
    small plastic bags or aluminum foil for penny containers
  • A few rubber bands
  • Two chairs
  • String: One 24″ and two 8″ pieces of string, plus extra string for more experiments
  • 20 or more pennies or other small objects of equal weight
  • A few paper clips
  • Pointy scissors

Film canister option: Carefully punch two holes in each lid with the scissors. Fasten the paper clip through the holes to create a hook. Put a few pennies in each canister and snap on the lids.
Plastic bag or aluminum foil option: Make a bundle to contain several pennies, and close the top with a rubber band. Shape the paper clip into a hook, and fasten each hook through the bundle’s rubber band, so you can hang this “container” by the paper clip hook.

Attach the long string tautly and high across the legs of two chairs. Tie a short string to each paper clip, and then tie each short string to the long string so the containers hang at equal lengths. gently pull one container towards you and release it. Let it swing for a while, and observe what happens.

  • What happens if you use unequal lengths of string?
  • Is there a difference with different weights in the containers?
  • What happens if you add more containers to the line?
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