1M40.33b-Conservation of Energy (small)


Video: Instructor’s video

Watch this 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 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.

NOTE: Often used in tandem with the other track. Students are more likely to guess correctly on this track, because they think the level part of the lower track allows the lower ball to “catch up” to the higher one. If they offer this explanation, you can pull out the other track!


  • 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.

Note: The two balls are found in the box attached to the track.