Council on Law Enforcement Education and Training (CLEET) Law Enforcement Driver Practice Test

What is Newton's third law of motion?

1. Energy cannot be created or destroyed

2. Mass times acceleration equals force

3. For every action, there is an equal and opposite reaction

4. Objects in motion tend to stay in motion

The correct answer is: For every action, there is an equal and opposite reaction

Newton's third law of motion articulates a fundamental principle that describes the relationship between forces and the objects upon which they act. Specifically, it states that for every action, there is an equal and opposite reaction. This means that when one object exerts a force on a second object, the second object simultaneously exerts a force of equal magnitude but in the opposite direction back on the first object. This principle is critical in understanding how forces interact in the physical world. For example, when a car accelerates forward, the tires push backward against the road, and in response, the road pushes the tires forward with an equal and opposite force. This action-reaction pair illustrates how forces must always occur in interactions, leading to motion or equilibrium depending on the context. The other statements pertain to different aspects of physics. The idea that energy cannot be created or destroyed relates to the conservation of energy, while mass times acceleration equating to force is Newton's second law of motion. Finally, the statement regarding objects in motion relates to inertia, which is explained by Newton's first law. Understanding these distinctions helps clarify why the third law specifically involves the concept of action and reaction.