The Moment Vector

Moment Vector

Effect of Force Angle


The moment about a point in 3-D space can be determined from the same basic scalar equation as in previous section on 2D scalar moments.

     Mo = r F

Here F is the magnitude of the force, and r is the perpendicular distance to the line of action of the force.

A force acting on a body in 3-D space tries to rotate the body in a plane defined by the force's line of action and the point under consideration. Since this plane is often difficult to visualize or define, a double-headed vector is used to define the axis about which the force is tending to rotate the body. The magnitude of the vector is the magnitude of the moment generated by the force.

The moment of a force in 3-D space can also be calculated using the Principle of Moments discussed in in the previous section. However, as it was seen, determining angles and distances in 3-D space can be very difficult. The next section will introduce a vector approach to calculating moments that greatly simplifies the process and reduces the number of steps necessary in calculating a moment vector.


Right Hand Rule
Moment vs Actual Rotation
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