Which law states that for every action there is an equal and opposite reaction?

• A. Newton's third law of motion
• B. Bernoulli's principle
• C. Archimedes' principle
• D. Pascal's law

Answer: (A)

Action-reaction force pairs are being tested here. For every force an object exerts on another, the second object exerts an equal magnitude force back on the first in the opposite direction, and these forces act on different bodies at the same time. This explains propulsion in flight: when a propulsion device pushes exhaust backward, the exhaust pushes the aircraft forward with equal force. The same idea shows up when you push against a wall or when a rocket or gun fires—there’s a backward push on the expelled mass and a forward push on the vehicle. Other choices describe different fluid phenomena: Bernoulli's principle links speed and pressure in moving fluids, Archimedes' principle concerns buoyant force, and Pascal's law deals with pressure transmission in confined fluids. The statement about equal and opposite forces in interactions is Newton's third law.