The law of interaction, also known as Newtons third law of motion, states that in every interaction, there is a pair of forces acting on the two interacting objects. The size of the forces on the first object equals the size of the force on the second object, and the direction of the force on the first object is opposite to the direction of the force on the second object. These forces always come in pairs, which are equal and opposite action-reaction force pairs. For example, when you sit in a chair, your body exerts a downward force on the chair, and the chair exerts an upward force on your body. The law of interaction helps us understand what happens when two moving forces meet and how different forces interact to create motion.