Video: Watch this demo
Bruce Yeany does this demo (small track starts at 1:02)
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.
Equipment:
- Track
- Two identical ball bearings
Demonstration Procedure:
- Release the balls from rest at the same time, from the start of the track.
Tips:
- 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!
- The two balls are found in the box attached to the track.
22-LEFT3
