Newton's Third Law of Motion states that when an object exerts a force on another object, the second object exerts a force of equal strength in the opposite direction on the first object.
With Newton's third law, objects exert force in action-reaction pairs. When a person jumps off the ground, they push down on the ground and the ground pushes up with an equal and opposite force.
If a man pushes a box, the box exerts an equal and opposite force on the man.
