The third law of motion, also known as Newton's third law, states that for every action, there is an equal and opposite reaction. Synonyms for this law include the law of action and reaction, the law of reciprocal actions, and the principle of reaction. The law is fundamental in physics and helps to explain how objects interact with each other. It applies not just in mechanics but also in other fields, such as electromagnetism and thermodynamics. Understanding this law is crucial in designing and developing technologies that rely on the interaction between objects, such as spacecraft and vehicles.