What is the name of the principle stating that for every action there is an equal and opposite reaction?

The principle that states for every action there is an equal and opposite reaction is known as the Law of Action-Reaction, which is part of Newton's third law of motion. This law illustrates the relationship between forces in a system, indicating that if one object exerts a force on another, the second object exerts an equal force in the opposite direction on the first object.

This concept is fundamental in understanding motion and forces in both physics and fitness training, as it explains how movements impact the body. For instance, when performing a squat, the force exerted downwards into the ground will result in an equal and opposite force pushing upward, which supports the body in its movement.

In contrast, other options refer to different principles of motion. The Law of Acceleration refers to Newton's second law, which states that the acceleration of an object depends on the mass of the object and the amount of force applied. Newton's Second Law specifically addresses how force affects the motion of an object rather than the equal and opposite forces of action and reaction. The Law of Friction pertains to the resistance encountered when two surfaces contact each other, which is unrelated to the action-reaction principle.