The law that states for every action there is an equal and opposite reaction is known as Newton's Third Law of Motion. This fundamental principle of classical mechanics emphasizes that forces always occur in pairs. When one object exerts a force on another, the second object simultaneously exerts a force of equal magnitude in the opposite direction. For example, when you push against a wall, your push exerts a force on the wall while the wall exerts an equal and opposite force back on you, demonstrating the balance of forces in action.