Sir Isaac Newton (1642-1727) realized that if one object applies a force on another, the second object applies the same amount of force on he first object, but in an opposite direction. This is called Newton’s Third Law of Motion. Since these forces are not opposed, they are said to be unbalanced.
An unbalanced force causes the object it is applied to move in the direction of the force. The diagram shows Newton’s third law of motion in action.
When the boy hits the golf ball with the golf club, the ball is pushed forward, and the golf club is pushed backward. The two forces, A and B as shown are needed to make these movements.
Notice that the arrows for the forces are equal in size, are in opposite directions, and are on different objects.
Force A is from the club hitting the ball.
Force B is from the ball hitting the club.
For example: In the figure, the identified action-reaction force pair is Force A/Force B.
Force A : “The club pushes against the ball.”
Force B: “The ball pushes against the club.”