Force may be defined as an agent which produces or tends to produce, destroy or tends to destroy the motion of a body.A force while acting on a body may
(a) change the motion of a body
(b) retard the motion of a body
(c) balance the forces already acting on a body
(d) give rise to the internal stresses in a body
In order to determine the effects of a force acting on a body, we must know the following characteristics of a force:
(a) Magnitude of a force
(b) The line of action of force
(c) The nature of force,i.e. pull or push
(d) The point at which the force is acting.
In M.K.S. system of units, the magnitude of force is expressed in Kilogram-force (kgf) and in S.I. system of units, the force is expressed in Newtons (N).
It may be noted that
1 kgf = 9.81 N