1M40.15-Pendulum and Peg


Video:  Watch this demo

MIT video showing that energy in an interrupted pendulum will never be lost 

Description: This is used to show the conservation of energy in a pendulum bob.


  • Table
  • One table clamp
  • One medium or long post
  • One s-clamp
  • One short, thin post (roughly the length of the pendulum clamp)
  • One adjustable-length pendulum clamp
  • String
  • One mass (roughly between 0.25kg and 1kg works best)

Setup Procedure:

  1. Clamp the medium/long post vertically to the table using the table clamp.
  2. Using the s-clamp, attach the short post horizontally about halfway up the medium/long post.
  3. Attach the pendulum clamp at the top of the medium/long post.
  4. Attach the string to the pendulum clamp and adjust it to be the correct length.
  5. Tie a loop at the bottom of the string and attach the mass to the string.
  6. Make sure the string swings and catches on the peg.

Demonstration Procedure:

  1. Optional: you can release the pendulum from rest without the peg in the way to show that, of course, the mass swings up to the same height on the other side before coming back.
  2. Release the pendulum from rest WITH the peg in the way to show that, because of conservation of energy, the mass still goes to the same height, even with a peg there to effectively shorten the string.