A rocket launch demonstrates Newton's third law (the rocket pushes down on the ground and the ground pushes back up). Which law is this an example of?

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

Answer: (C)

Think about forces that happen in pairs when two objects push on or push back against each other. This is Newton’s third law: for every action, there is an equal and opposite reaction, and the two forces act on different objects.

In a rocket launch, the rocket pushes exhaust gases downward. The exhaust, in turn, pushes the rocket upward with a force of the same size but in the opposite direction. That pairing of forces is why the rocket accelerates upward—the thrust you feel comes from this action-reaction interaction. If you imagine the rocket pushing on the ground and the ground pushing back, you’re seeing the same principle at work: two objects interact, and the forces on them are equal in magnitude and opposite in direction.

The other laws describe different ideas: Newton’s first law is about inertia when there’s no net force, Newton’s second law connects net force to how fast an object accelerates, and the law of conservation of energy deals with how energy is transformed rather than the interaction forces between bodies.