The speed of the induction generator will vary with the rotational force (moment, or torque) applied to it by the winds energy but it will continue to generate electricity until its rotational speed falls below idle. In practice, the difference between the rotational speed at peak generating power and at idle, (synchronous speed) is very small, only a few percent of the maximum synchronous speed. For example, a 4-pole generator with a synchronous idle speed of 1500 rpm attached to the utility grid with a 50 Hz current, may produce its maximum generated power rotating at only 1-to-5% higher, (1515 to 1575 rpm), easily achieved using a gearbox.