Reduction of Forces

the transformation of a system of forces applied to a rigid body into another, equivalent system, in particular, a simpler one. In general, any system of forces, when reduced to an arbitrary point (the point of reduction), can be replaced by a single force (the resultant force) equal to the geometric sum of the forces in the system and applied to the point of reduction, and by a single couple with a moment (the resultant torque) equal to the geometric sum of the moments of all the forces relative to the point of reduction.