THE LAW OF THE PENDULUM
In college a student was asked to prepare a lesson to teach his speech class. He was to be graded on creativity and ability to drive home a point in a memorable way. The title of his talk was, “The Law of the Pendulum.” He spent twenty minutes carefully teaching the physical principle that governs a swinging pendulum. The law of the pendulum is: A pendulum can never return to a point higher than the point from which it was released. Because of friction and gravity, when the pendulum returns, it will fall short of its original release point. Each time it swings it makes less and less of an arc, until finally it is at rest. This point of rest is called the state of equilibrium, where all forces acting on the pendulum are equal.
The student attached a three-foot string to a child’s toy top and secured it to the top the blackboard with a thumbtack. He pulled the top to one side and made a mark on the blackboard where he let it go. Each time it swung back he made a new mark. It took less than a minute for the top to complete its swinging and come to rest. When he finished the demonstration, the markings on the blackboard proved the law of the pendulum.
The student then asked how many people in the room believed the law of the pendulum was true. All of his classmates raised their hands and so did the teacher. The teacher started to walk to the front of the room thinking the class was over. In reality it had only begun. Hanging from the steal beams in the middle of the room was a large, crude but functional pendulum made from 250 pounds of metal weights tied to four strands of 500 pound test parachute cord. The student invited the instructor to climb up on a table and sit in a chair with back of his head against a cement wall. Then the student brought the 250 pounds of metal up to the teachers’ nose. Holding the huge pendulum just a fraction of an inch from the teacher’s face, the student once again explained the law of the pendulum he had applauded only moments before, “If the law of the pendulum is true, then when I release this mass of metal, it will swing across the room and return short of the release point. Your nose will be in no danger.”
After that final restatement of this law, the student looked his teacher in the eye and asked, “Sir, do you believe this law is true?” There was a long pause. Huge beads of sweat formed on his upper lip and then weakly
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