Page 20 - mechanics

Chapter – 4 Non-Concurrent forces and Moments

body is placed at any point on its line of action. This principle

is based on experimental evidence.

4.1.1 Moment of a force about a point

We need to specify the magnitude and direction of the

moment vector. Moment of a force about a point has a

magnitude that equals the product of the force magnitude and

the perpendicular distance from the point to the force line of

action. Let MO denote the moment vector about point O, then

MO = F d (4.1)
MO: is the magnitude of the moment about point O.

F: is the magnitude of the applied force.

d: is the perpendicular distance from point O to the line of

action of the force (see Figure (4.1)). This distance is usually

called the moment arm. From equation (4.1), the unit of the

moment magnitude is of force unit times distance unit (N.m).

O F
d

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