Question

Professor Walter Lewin, for his famous Physics experimental demonstration, hanged a bowling ball from the ceiling by a rope. He then pulls the ball away from its equilibrium position and holds it adjacent to his nose, as shown. He releases the ball so that it swings directly away from him. Does he get struck by the ball on its return swing? What is he trying to show in this demonstration?

Answer 1

No, he didn't get struck by the ball on its return swing. This is due to principle of conservation of mechanical energy. If there is no dissipative forces on the system total mechanical energy which is given by sum of kinetic and potential energy is conserved. When proff Lewin released the ball at some height, after the return swing the maximum height reached by the ball will be same, it can't be greater otherwise it will violate conservation of energy. In fact in the room there wilere dissipative forces for instance the drag force due to air, because of this the ball reached slightly less maximum height than earlier. But the point is, it can't reach a height higher than it started with.