What is the key concept of Newton's Third Law?

Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. This means that when one object exerts a force on a second object, the second object exerts a force of equal magnitude but in the opposite direction back onto the first object. This principle can be observed in various scenarios, such as a rocket launching into space; as the rocket engine pushes downward against the ground through the expulsion of gas, the rocket itself is propelled upward. Understanding this concept is crucial as it underlies many interactions and forces in our physical world, emphasizing the interconnectedness of action and reaction.

The other choices do not accurately represent Newton's Third Law. The first option focuses on acceleration, which pertains to Newton's Second Law, while the third option misrepresents forces as unchangeable. The fourth option suggests a limitation on how forces act only when objects are in motion, which ignores the fact that forces can act on stationary objects as well. Thus, the correct understanding of Newton's Third Law lies in recognizing that every action inevitably invites a counteraction of equal force but in the opposite direction.