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Chapter – 4 Non-Concurrent forces and Moments
perpendicular distance (the moment arm) between the force
and the moment axis. Then, a force F will only cause a moment
about an axis AB if it is perpendicular to the plane containing
that axis and the moment arm d. In this case, the magnitude of
the moment about the axis is given by
MAB = F d (4.9)
and directed along axis AB with a positive sign if the right hand
rule points with positive direction of AB or else it is negative.
B
A
MAB
B
A
MAB
Fig 4.7 Positive and negative moments about axis AB.
Another, and definitely a much easier approach, is by vector
analysis. Remember that the moment about a point is a vector
that has Cartesian components. Thus the moment of a force
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