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A bowling ball is suspended from the ceiling by a thin stainless steel wire. The "victim" stands with the back of his head against a wall with a bowling ball held snugly against his nose. The bowling ball is released (not pushed!), and the ball swings back to within a few centimeters of the nose.
If the victim is selected from the audience, then a point on the wall can be marked ahead of time to indicate the proper position for the head. The selected person should be of approximately the correct height, or a step stool can be used. It is best if the pendulum is as long as possible, if the victim is far back from the point of suspension and if the audience views from the side. Protective gear on the victim can add to the drama, so long as the face is still exposed.
This illustrates the conservation of energy for a closed system. The potential energy acquired when the ball is lifted above its resting position is transformed into kinetic energy as the ball's velocity increases, and back again. Small energy losses are due to air resistance and friction at the wire’s pivot point.
This demonstration works for low to middle level audiences of all sizes. Securing a bowing ball pendulum is the most difficult part; the demonstration itself is fairly simple.
Shock Value: 4