Which law applies when a ship fires a cannonball and the ship recoils?

Which law applies when a ship fires a cannonball and the ship recoils?

• A. The Law of Inertia
• B. Law of Universal Gravitation
• C. Newton's Third Law of Motion
• D. Newton's Second Law of Motion

Answer: (C)

When one object pushes on another, there is a matching push in the opposite direction. Firing the cannonball forward is caused by the gases pushing on the ball, and the ball pushes back on the cannon with an equal and opposite force. That reaction force acts on the cannon—and since the cannon is attached to the ship, it transfers to the ship—so the ship recoils backward. Because the ship plus cannon are much heavier than the ball, the recoil speed is small even though the ball speeds away. This is Newton's Third Law in action: every action has an equal and opposite reaction. The other ideas don’t explain why the recoil happens in the first place—inertia is about resisting changes in motion, gravity acts downward between masses, and while Newton's Second Law would tell you how the accelerations relate to the forces, the immediate cause of the recoil is the action–reaction pair.

When one object pushes on another, there is a matching push in the opposite direction. Firing the cannonball forward is caused by the gases pushing on the ball, and the ball pushes back on the cannon with an equal and opposite force. That reaction force acts on the cannon—and since the cannon is attached to the ship, it transfers to the ship—so the ship recoils backward. Because the ship plus cannon are much heavier than the ball, the recoil speed is small even though the ball speeds away.

This is Newton's Third Law in action: every action has an equal and opposite reaction. The other ideas don’t explain why the recoil happens in the first place—inertia is about resisting changes in motion, gravity acts downward between masses, and while Newton's Second Law would tell you how the accelerations relate to the forces, the immediate cause of the recoil is the action–reaction pair.