Demos: 1M-01 Bowling Ball Pendulum

This demonstration is an entertaining and dramatic way to illustrate the conservation of mechanical energy. The demonstrator stands against the door and pulls the bowling ball back to touch his/her nose. The ball is released, swings out and returns to approximately the same position. Because no positive work is done on the ball, there is no gain in total energy, thus the ball cannot reach a higher point than it started. The demonstrator is safe (if he doesn’t step forward!).

Directions: Brace your body against the door and hold the ball against your nose. Release the ball (DO NOT PUSH IT!) and stay still. It will head back to your nose, but actually stop just short of it because of frictional losses in the system.

Suggestions for Presentation: Begin by expressing “Faith in the Conservation of Energy!” Hold the ball against your nose and ask whether it would be safe to remain standing there after the ball is released. Once you have performed this, then explain that the ball actually came back a little short because negative work was done on the ball as it plowed through the air.

Applications: Compare this with other pendulum-type motions that obey the conservation of energy.

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