Law of Interaction states that when an object exerts a force on another object, the second object exerts on the the first a force of the same magnitude but in the opposite direction.
The law of interaction states that 'every force in nature has an equal and opposite reaction meaning there always a back force like for example firing a sniper rifle the force that is opposite to the force of the bullet would be the recoil or like opening a really strong hose its so strong you could be pushed back by the counter force