Conservation of Angular Momentum

The conservation of angular momentum has interesting consequences. Here we show two demonstrations that will clarify them.

1. Because the angular momentum is the product of the moment of inertia and the angular velocity, it can remain a constant while the the moment of inertia increases or decreases. What happens is that the angular velocity must decrease or increase accordingly. We show this effect here using a chair which rotates almost friction free on ball bearings. One of the authors is sitting on the chair and changes his moment of inertia by moving weights in his hands in and out. You can clearly see that his angular velocity is changing accordingly.

2. In the second demonstration, one of the authors is holding a fast spinning wheel in his hands. This wheel has angular momentum, a vector quantity. When he reverses the axis of rotation of the wheel, he imparts angular momentum to himself. Because the total angular momentum of the man plus wheel must remain a constant, the man must spin in the same direction as the wheel did originally.