Question

If action and reaction are always equal and opposite, why don't they always cancel one another and leave no net force for accelerating a body?

Answer 1

Action and Reaction Forces:

1. According to Newton's law of motion, every action has an equal and opposite reaction.
2. They are always equal and opposite but they do not act upon the same body.
3. As they are acting on different bodies, they can not cancel one another.
4. For example, the swimmer pushes against the water in order to move forward (action force) while swimming.
5. The water pushes back on the swimmer in order to help the swimmer to move in the forward direction (reaction force).
6. The diagrammatic representation of the forces acting while swimming is given below:

Hence, the action and reaction forces do not cancel each other because they act on different bodies at the same time.