Force Couples: A force couple consists of two parallel forces of equal magnitude and opposite direction separated by a finite distance. The net result is a couple moment of magnitude M = Fd. It is important to realize that a couple moment is a free vector meaning that it can be shown at any point on the body as long as its magnitude and direction are not altered.

Force couples appear in many problems, and they represent a practical way for applying moments on a body. For example, when one uses a cross wrench to loosen or tighten the lug nuts on a wheel of a car, the applied forces at the opposite ends of the cross wrench form a couple. Also by having both hands on the steering wheel of a car, we can apply a couple to turn the wheel. 