From times immemorial, man has used machines to help him in his work. Today, we are dependent on machine for almost every task. When we think of machines we always tend to think of big and complicated units with many moving parts like wheels and rollers and gears and shafts. A bicycle is a machine which is used to gain speed. We gain speed by exerting additional force. When we try to ride a bicycle up a steep hill, we soon realize that we gain speed by applying greater force. It is impossible to multiply both the force and gain the speed at the same time.