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تسجيل

The Moment of a Force

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  p-57

2025-11-02

525

 Suppose there are two forces, F and F", acting at right angles to the bar AB, each tending to rotate it about the pivot C (Fig. 1). It is evident that the tendency of each force to produce rotation depends not only upon the magnitude of the force, but also upon its distance from the point C, about which it tends to turn the bar. If the distance CA is d, and CB is d', the tendency to produce rotation exerted by F is proportional to the product Fd, which is called the moment of the force F; so, too, the moment of the force F' is F'd'. The point C, about which the rotation takes place, is called the center of moments. The force F' tends to produce a clockwise and the force F a counterclockwise rotation around the point C.

 If the forces F and F′ do not act in a direction that is perpendicular to the bar AB, as in Fig. 2, then the distances d and d' will not be CA and CB, but CD and CE, which are the perpendiculars drawn from C to the directions of the forces. The moment of a force is the product of the force by the perpendicular distance from the center of moments to the direction of the force.