Q: A coin is put on the turntable of a record player . The motor is started , but before the final speed of rotation is reached , the coin flies off . Why?
Sol: In the beginning , the frictional force provides the necessary centripetal force to keep the coin on the circular path . With increasing speed , the frictional force also increases . This continues until limiting friction is reached , and exceeded . Then the coin flies off tangentially relative to an observer on the ground , the limiting frictional force now being unable to provide the necessary centripetal force .