03-16-09

An objects mass depends on both its ordinary mass and how the mass is distributed within the object. 1. If the rotating object has more mass, the object will have more rotational inertia. 2. If a rotating objects mass moves closer to the axis of rotation, the object will experience a slower rotational speed. 3. If a rotating objects mass moves closer to the axis of rotation, the object will have rotational inertia.

Friction causes the spheres and disks to roll down the incline plane.

Spheres always win because they have more mass and they have more friction on the surface.

Dan shows how rotational inertia effects movement. In the picture above, with his hands out, he goes slower. In the picture below, with his hands in the center, rotational inertia causes him to move faster. This is used in figure skating when the skater jumps. If you watch the skater closely, when just before the skater jumps her arms are out causing her radius to be greater, when she pushes off her feet with some force and brings her arms closer, causing her radius to be smaller, she spins.