The relationship between the speeds of the first and last shafts, respectively, of a train of gears. If a certain force drives a machine at a given speed and the output shaft runs at one-tenth of the speed of the input shaft, then the output force will be 10 times the input. If the gear ratio of a motor-driven machine is 10 to 1, then the turning force of the last shaft will be 10 times that of the motor, apart from force used up in friction.