A moment of a force is defined as the product of the force and the perpendicular distance of the force from a pivot. where the force, is perpendicular to the displacement, .
If the force and displacement are not perpendicular then the moment of the force is given by
where is the angle between the force and the displacement.
Or in vector notation
For equilibrium both the sum of the forces and the sum of the moments must be zero, i.e., and