Question

What is force? How do two bodies exert force on each other?

Answer 1

In physics, a force is any interaction that, when unopposed, will change the motion of an object.[1] A force can cause an object with mass to change its velocity (which includes to begin moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a push or a pull. A force has both magnitude and direction, making it a vector quantity. It is measured in the SI unit of newtons and represented by the symbol F.

Newton’s Third Law of Motion states: ‘To every action there is an equal and opposite reaction’.
It must be remembered that action and reaction always act on different objects. The Third Law of Motion indicates that when one object exerts a force on another object, the second object instantaneously exerts a force back on the first object. These two forces are always equal in magnitude, but opposite in direction.
These forces act on different objects and so they do not cancel each other. Thus, Newton’s Third Law of Motion describes the relationship between the forces of interaction between two objects.
Whenever two bodies interact with each other, the force exerted by the first body on the second is called action. The force exerted by the second body on the first body is called reaction. The action and reaction are equal and opposite.
For example, when we placed a wooden block on the ground, this block exerts a force equal to its weight, W = mg acting downwards to the ground. This is the action force. The ground exerts an equal and opposite force W’ = mg on the block in the upward direction. This is the reaction force.