Ans. It is a graphical method of finding the resultant of two forces, according to the following law: If two forces acting on a point be represented in direction and intensity by adjacent sides of a parallelogram, their resultant will be represented by the diagonal of the parallelogram which passes through the point.
Fig. 2,124.—Parallelogram of forces. OC is the resultant of the two forces OA and OB. The length and direction of the lines represent the intensity and direction of the respective forces, the construction being explained in the accompanying text.
Thus in fig. 2,124, let OA and OB represent the intensity and direction of two forces acting at the point O, Draw AC and BC, respectively parallel to OB and OA, completing the parallelogram, then will OC, the diagonal from the point at which the forces act, represent the intensity and direction of the resultant, that is, of a force equivalent to the combined action of the forces OA and OB, these forces being called the components of the force OC.
Ques. Upon what does the magnitude of the resultant of two forces depend?
Ans. Upon the difference in directions in which they act, as shown in figs 2,125 to 2,128.
Ques. Is the parallelogram of forces applied when the difference in direction or "phase difference" of two forces is 90 degrees?
Ans. It is sometimes more conveniently done by calculation according to the law of the right angle triangle.
