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

The key principle of Newton's Third Law is that for every action, there is an equal and opposite reaction. This means that whenever one object exerts a force on another object, the second object exerts a force of equal magnitude but in the opposite direction on the first object. This principle is fundamental in understanding interactions between objects. For instance, when you push against a wall, the wall pushes back against you with an equal force, which is why you do not move through the wall.

This law highlights the nature of forces as interactions rather than just the isolated action of a single object. It helps to explain many phenomena in mechanics, such as propulsion, collisions, and the behavior of objects under various forces. Understanding this principle is essential for solving problems related to motion, force, and reaction forces in physical science.