Chetak knew only that action and reaction are equal and opposite. But since Sam had secured 100/100 marks in physics, he very well knew that action and reaction act on different bodies. So he patiently explained to Chetak about forces which is as under....
Suppose the horse pulls the cart by a force F1 in the forward direction and the cart exerts the force F2 on the horse in the backward direction Here F1 =F2
We should first decide the system. If we take the horse as our system then we should consider only those forces which are acting on the horse. Since force f1 is on the cart we do not consider it but we have to consider the force f2 which acts on the horse. Then a question arises that why the horse goes forward when the force f2 on it is acting backward? The answer to this question is that still we have not considered all the forces acting on the horse.
In these process three action-reaction pairs are there...
- a pair of forces exerted by the horse on the cart and that by the cart on the horse.
- a pair of forces exerted by the horse on the ground and that by the ground on the horse.
- a pairs of forces exerted by the cart on the ground and that by the ground on the cart.