1M40.33a-Conservation of Energy (large)

Video:  Watch this demo

Instructor’s video

Bruce Yeany does this demo (large track starts at 2:01)

Brown triple track demo

Description: When two identical balls are simultaneously released from rest at the same position, most students guess that the ball on the top track (the straight track) will win, perhaps because it is a much shorter path. In fact, the bottom track wins, because the ball traveling along the lower path has a higher kinetic energy and a higher horizontal velocity the entire time it is traveling at a lower gravitational potential energy, despite the fact that both balls have the same initial and final kinetic energies, and thus the same FINAL velocity.


  • Track
  • Two identical ball bearings

Demonstration Procedure:

  1. Release the balls from rest at the same time, from the start of the track.
  2. Make sure someone is at the other end to catch the balls.


  • Often used in tandem with the other track (1M40.33b). This track is the LESS intuitive of the two, because it does not have a level stretch on the lower track along which the ball could “catch up”.
  • The two balls are found in the box on the other track.