about
a point is the cross product of the vector
from
the point in question to point of application of the force with the
force, that is
A Level Maths Notes: M5 – Finding the Moment of a Force About a Point in Three Dimensions
The torque or moment of a
forceabout
a point is the cross product of the vectorfrom
the point in question to point of application of the force with the
force, that is
For example, the moment
of
acting
at
about
the point
is
Properties:
The moment is at right angles to both
and
This
is a consequence of the cross product. In the above diagram the
moment is directed out of the paper, since the cross product defines
a right handed coordinate system.
If a force acts at a point, the moment of the force about that point is zero.
The total moment of a system of forces is equal to the sum of the
moments:
The Total Moment is a vector, with magnitude given by
where
is
the acute angle betweenand