What is Newton's third law?

Newton's third law states that for every action, there is an equal and opposite reaction. This principle highlights the relationship between forces acting on two bodies. When one body exerts a force on another, the second body simultaneously exerts a force of equal magnitude and opposite direction back on the first body. This interaction is key in understanding motion and force balance in various physical systems.

In practical terms, this law can be observed in everyday situations, such as when you push against a wall; the wall pushes back against you with equal force. This principle is foundational in physics and helps explain phenomena in mechanics, such as propulsion and collision dynamics. It also underscores the reciprocal nature of forces, which is crucial in fields like engineering and physics.

Other options, while related to important concepts in physics, describe different principles. One speaks to inertia (Newton's first law), another relates force, mass, and acceleration (Newton's second law), and the last addresses conservation of energy, which falls under a different category of physical laws. Hence, Newton's third law is specifically and uniquely defined by the concept of action and reaction pairs.