Which scenario best demonstrates an action-reaction pair?

Which scenario best demonstrates an action-reaction pair?

• A. A rocket expelling gas backward
• B. A person pushing a wall
• C. Both illustrate action-reaction pairs
• D. Neither illustrate action-reaction pairs

Answer: (C)

The scenario tests Newton’s third law: for every force there is an equal and opposite force acting on the other object involved in the interaction. These action and reaction forces happen at the same time and act on two different objects. In the rocket example, the engine pushes on the expelled gas backward, and the gas pushes on the rocket forward with the same magnitude in the opposite direction. That forward push on the rocket is the thrust that propels it. In the wall example, the person pushes the wall, and the wall pushes back on the person with equal magnitude in the opposite direction. That push is the resistance the person feels. Since both cases involve a pair of forces on two different objects, both illustrate action-reaction pairs. The fact that the wall is anchored to the ground doesn’t negate the pair—the forces still act on two separate bodies.

The scenario tests Newton’s third law: for every force there is an equal and opposite force acting on the other object involved in the interaction. These action and reaction forces happen at the same time and act on two different objects.

In the rocket example, the engine pushes on the expelled gas backward, and the gas pushes on the rocket forward with the same magnitude in the opposite direction. That forward push on the rocket is the thrust that propels it.

In the wall example, the person pushes the wall, and the wall pushes back on the person with equal magnitude in the opposite direction. That push is the resistance the person feels.

Since both cases involve a pair of forces on two different objects, both illustrate action-reaction pairs. The fact that the wall is anchored to the ground doesn’t negate the pair—the forces still act on two separate bodies.