PHYSICS   LECTURE   DEMONSTRATIONS

M-E3   :   Twin Balls

UNIT: Mechanical Energy, Collisions
PURPOSE: Bring into sharp focus the difference between two apparently "similar" events, one in which mechanical energy is (nearly) conserved and another in which it is not.
EQUIPMENT: Two apparently identical, small black balls, one "happy" the other "sad"
SUGGESTIONS:
1. Drop the "happy" ball on the tabletop
2. Drop the "sad" ball on the tabletop 
3. Ask students what is different between the two collisions. Where did the mechanical energy go in the second case?
DISCUSSION: The only difference in the appearance of the balls is that one is shinier than the other

1.                  2.
 

1. Both balls being released from the same height
2. After the collision, "happy" ball on its way up while "sad" remains on the table