PHYSICS   LECTURE   DEMONSTRATIONS

M-S2   :   Dumbbell Molecule

UNIT: Center of mass
PURPOSE: Show how CM can simplify the description of motion
EQUIPMENT:
1. Dumbbell model (two balls of different size and mass connected by a rigid light rod) OR
2. Two unequal hacky sacks connected by a string
3. CM marker
SUGGESTIONS: Discuss motion of CM and motion relative to CM for 
1. Dumbbell dropped from rest
2. Rotation with one mass at the center
3. Dumbbell thrown spinning in the air
DISCUSSION: For cases 1 and 3, the center of mass moves like a projectile as if it were a point particle of mass equal to the total mass of the system.

1.                              2.                              3.
  

1. Hacky sacks with the CM marker
2. Dropping the hacky sacks aligned vertically
3. In flight, with the CM marker describing a parabola and the two sacks rotating about it.