The effect of the location of a force is known as the
MOMENT OF FORCE. It is equal to the force
multiplied by the distance from an axis about which
you want to find its effect. The moment of a force is the
tendency of the force to produce rotation or to move the
object around an axis. Since the force is expressed in
terms of weight units, such as tons or pounds, and the
moment is force times distance, the units for moment
are expressed as foot-tons, foot-pounds, or
inch-ounces.
In figure 12-6 the moment of force (F) about the
axis at point a is F times d; d being called the moment
arm. The moment of a force can be measured about any
point or axis; however, the moment differs according to
the length of the moment arm. It should be noted that
the moment of a force tends to produce rotary motion.
In figure 12-6, for example, the force F produces a
clockwise rotation. If, at the same time, an equal and
opposite force produces a counterclockwise rotation,
there will be no rotation; and the body is in
equilibrium.