Illustrate the law of conservation of energy by discussing the energy changes which occur when we draw a pendulum bob to one side and allow it to oscillate. Why does the bob eventually come to rest? What happens to its energy eventually? Is it a violation of the law of conservation of energy?
In given figure a pendulum is hinged at point P, when pendulum moves from its mean position O to either of its extreme positions A or B, it rises through a height h above the mean level O. at this point, the kinetic energy(KE) of the bob changes completely into potential energy(PE). The KE becomes zero and the bob possesses only PE. When bob moves towards point O, it PE decreases and KE increases. When bob reaches at point O, PE becomes zero and only have KE. Same process is repeats as long as pendulum oscillates. Part(b) It comes to rest because of air resistance. The pendulum loses its KE to overcome the air friction and stops after some time. Part(c) Law of conservation of energy is not violated because the energy lost by the pendulum to overcome air friction is gained by its surroundings. Hence, total energy of system + surroundings remains constant.
