Page 19 - mechanics

Chapter – 4 Non-Concurrent forces and Moments

4.1 Moment

What is the difference between the force effects on a particle
(point) and on a body?

On a point particle, the only possible effect a force might
have is translation. This means that if the force is large enough
it may move the particle to a new position along its line of
action. Yet, when a body is subjected to a force, it may move
or rotate. A force thus has two effects on bodies: translational
and rotational.

The moment of a force is the measure of its tendency to
cause rotation. Moments cause the rotation of machinery such
as the wheels of a vehicle, crankshafts, and turbines. Like
force, moment is also a vector and to study the state of bodies
now, we have to consider both of them. For example,
equilibrium cannot be defined now as the resultant of forces
acting on the body equals zero as this could be the case yet the
body is rotating under the effect of moments. In subsequent
sections we study moments in two and three dimensions and
we begin by stating the principle of transmissibility.

The principle of transmissibility states that the conditions
of equilibrium or of motion of a rigid body will remain
unchanged if the force F acting at a given point of the rigid

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