equilibrium (zero net external force) but also rotational equilibrium (zero net external torque), as we shall see in Chapter . Answer Figures . (b) and . (c) are known as free-body diagrams.
Figure . (b) is the free-body diagram of W and Fig. . (c) is the free-body diagram of point P.
Consider the equilibrium of the weight W. Clearly, T = × = N. Consider the equilibrium of the point P under the action of three forces - the tensions T and T , and the horizontal force N. The horizontal and vertical components of the resultant force must vanish separately : T cos θ = T = N T sin θ = N which gives that Note the answer does not depend on the length of the rope (assumed massless) nor on the point at which the horizontal force is applied.
. COMMON FORCES IN MECHANICS In mechanics, we encounter several kinds of forces. The gravitational force is, of course, pervasive. Every object on the earth experiences the force of gravity due to the earth.
Gravity also governs the motion of celestial bodies. The gravitational force can act at a distance without the need of any intervening medium. All the other forces common in mechanics are