The Forces

Force is a word that we have all heard about. When you push or pull some object, you exert a force on it. If you push a body, you exert a force away from yourself; when you pull, you exert a force toward yourself. When you hold a heavy block in your hand, you exert a large force; when you hold a light block, you exert a small force. Can nonliving bodies exert a force? Yes, they can. If we stand in a great storm, we feel that the wind is exerting force on us. When we suspend a heavy block from the rope, the rope holds the block just as a man can hold it in the air. When we comb our dry hair and come close to a small piece of paper, the pieces jump to the comb. The come has attracted the paper pieces, i.e., the comb has exerted force on the pieces.

The SI unit for measuring the force is called a newton. Approximately, it is the force needed to hold a body of mass 102 g near the earth's surface. 

Force is an interaction between two objects. Force is exerted by object A on another object B. For any force, you may ask two questions, (i) who exerted this force, and (ii) on which object was this force exerted? Thus when a block is kept on a table, the table exerts a force on the block to hold it.

Force is the vector quantity, and if more than one force act on the particle, we can find the resultant force using the laws of vector addition. Note that in all the examples quoted above, if body A exerts a force on B, body B also exerts a force on A. Thus, the table exerts a force on the block to hold it, and the block exerts a force on the table to press it down. Similarly, When a heavy block is suspended by a rope, the rope exerts a force on the block to hold it, and the block exerts a force on the rope to make it tight and stretched. In fact, these are a few examples of Newton's third law of motion, which may be stated as follows.

Newton's Third Law of Motion

If body A exerts a force F on another body B, then B exerts a force -F on A, the two forces acting along the line joining the bodies.

The two forces F and -F, connected by Newton's third law called the action-reaction pair. Anyone may be called 'action" and the other 'reaction.'

We shall discuss this law in greater detail in the next Topic. The various type of force in nature can be grouped into four categories:

(a) Gravitational           (b) Electromagnetic,

(c) Nuclear            and  (d) Weak. 

To be continued.........