Page 21 - mechanics

Chapter – 4 Non-Concurrent forces and Moments

4.2 Moment of a Force about a Line (Axis)

The concept of moment about a line is first mentioned when
writing the moment vector in its Cartesian form. We figured
out that like the force components represent forces acting in the
direction of the coordinate axes, moment components represent
moments about coordinate axes as well. The moment of the
force about the line is the measure of the tendency of a force
to cause rotation about that line. An object rotating about a
line (axis) by a fore can be seen in many cases such as a turbine
shaft that rotates about an axis, a wind turbine, a glass globe or
even a revolving door. But not all forces can cause a body to
rotate about an axis. If the force passes through the axis or it is
parallel to it, it causes no moment about the axis.

Fig. 4.6 Rotations about axis.

Following our standard notation, denote by d the

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