The third law of motion states that for every action, there is an equal and opposite reaction. This means that in every interaction, there is a pair of forces acting on the two interacting objects. The magnitude of the force acting on the first object is equal to that on the second object, but the direction is opposite. For example, a gun recoils when a bullet is fired from it. When the bullet is fired, the gun exerts a force on the bullet in the forward direction. In reaction to this, the bullet also exerts an equal force on the gun in the backward direction.