Parallelogram of Forces

a geometric representation of the law of composition of forces. The law of parallelogram of forces states that the vector representing the force equal to the geometric sum of two forces is given by the diagonal of a parallelogram whose sides are the vectors of the two forces. Thus, when two forces are applied to a body at the same point, the resultant of the forces can be found by constructing a parallelogram of forces. In dynamics this result is valid only for motion at velocities much less than the velocity of light.