What principle states that every action has an equal and opposite reaction?

The principle that states every action has an equal and opposite reaction is known as Newton's Third Law of Motion. This law emphasizes the interaction between two objects. When one object exerts a force on another, the second object exerts a force of equal magnitude but in the opposite direction on the first object. This fundamental principle illustrates the nature of forces and how they operate in pairs, contributing to our understanding of how objects move and interact in physical systems. For example, if you push against a wall, the wall pushes back against you with the same amount of force, allowing us to understand the balance and conservation of momentum in different scenarios.