# Moment of a Force

Moment Resultant

Scalar Representation: Consider force acting at point A. The magnitude of the moment of this force about point B is determined from the scalar product

 (1)

where F is the magnitude of the force, and d is the perpendicular distance between point B and the line of action of the force. Distance d is commonly referred to as the moment arm of the force while point B is called the moment center.

In this case, the moment about point B can be interpreted as the measure of the tendency of force F to cause the body to rotate about B. The key word is tendency. It is not necessary for the body to actually rotate about B for the moment to be created. The sense of the moment is determined based on the right-hand rule. The axis of the moment vector is perpendicular to the plane containing and d.

To calculate the moment of a force using the scalar approach, we must know:

Force magnitude

Location of the moment center

Perpendicular distance from the moment center to the line of action of the force

Example 1

Moment Resultant