Answer:
Action force and reaction force
Step-by-step explanation:
According to newton's third laws of motion, the action of a body is always associated with the reaction of the other body.
But these two forces don't act on the same body.
For example,
If a man hits on the wooden board with his fist, he exerts a certain amount of force on the surface of the board. Consider it as action force dented by 'Fa'.
The wooden board exerts a similar force that is equal in magnitude but in the direction opposite to the applied force on his fist. Consider it as action force dented by 'Fr'.
In both cases, the force is acting on different bodies. It is mathematically expressed as
Fa = - Fr