For every action there is an equal and opposite reaction.

• A. Newton's First Law
• B. Newton's Second Law
• C. Conservation of Momentum
• D. Newton's Third Law

Answer: (D)

When two objects interact, forces come in pairs: the force one object exerts on the other has an equal magnitude but opposite direction to the force the second object exerts back. These action-reaction forces act on different objects and occur at the same time, so you can feel the push and the pushback in any interaction, like you pushing off the ground to jump, or a rocket ejecting exhaust to propel itself forward.

This idea is Newton's Third Law. It differs from the First Law, which is about an object continuing its motion or staying at rest unless a net external force acts on it. It also differs from the Second Law, which relates the net force to how much an object accelerates (F = ma). Conservation of Momentum deals with the total momentum in a system over time, not the existence of paired forces themselves.