Demos: 1D-03 Demonstrations of Central Force

A large rotating wheel can accept a variety of objects to show the effects of the central force.

1. a strap spring sphere, when rotated, becomes oblate and illustrates, for example, the flattening of a planet as it spins;
2. Water in a spherical glass container takes on a smooth parabolic surface;
3. Two balls of different masses can slide on a bar. If the axis of rotation passes through the CG, the balls will not slide on the rod.

Directions: Each of the objects, in turn, are placed into the central hole in the wheel. The lock nut is tightened and the wheel is turned manually using a crank.
Suggestions for Presentation: Ask the students what will happen when such things as water surfaces semi-rigid objects, etc are subjected to forces during rotation. You might want to bring up planets and ask about their shapes, especially Jupiter.
Applications: (a) Planetary shapes; (b) a concave mercury mirror has been used in a telescope. The mercury is rotated at a speed that gives the required curvature; (c) the vibrations of out-of-balance systems.

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