Which of Newton's laws explains action-reaction pairs such as pushing against a wall and the wall pushing back?

Which of Newton's laws explains action-reaction pairs such as pushing against a wall and the wall pushing back?

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

Answer: (D)

Action-reaction pairs come from Newton's Third Law: for every force there is an equal in magnitude and opposite in direction force that acts on a different object. When you push on a wall, your hand exerts a force on the wall, and the wall pushes back on your hand with the same strength in the opposite direction. These two forces are paired and simultaneous, and they act on two separate bodies, so they don’t cancel each other out. The other laws describe different ideas. The universal gravitation law explains how masses attract each other, not the existence of paired contact forces. Newton's first law (inertia) tells us about motion staying the same unless a net force acts, not about paired forces. Newton's second law links the net force on an object to its acceleration, F = ma, but it doesn’t describe the existence of action-reaction force pairs. So, the explanation for action-reaction forces—the fact that you feel resistance when pushing and the wall pushes back with equal force—is Newton's Third Law.

Action-reaction pairs come from Newton's Third Law: for every force there is an equal in magnitude and opposite in direction force that acts on a different object. When you push on a wall, your hand exerts a force on the wall, and the wall pushes back on your hand with the same strength in the opposite direction. These two forces are paired and simultaneous, and they act on two separate bodies, so they don’t cancel each other out.

The other laws describe different ideas. The universal gravitation law explains how masses attract each other, not the existence of paired contact forces. Newton's first law (inertia) tells us about motion staying the same unless a net force acts, not about paired forces. Newton's second law links the net force on an object to its acceleration, F = ma, but it doesn’t describe the existence of action-reaction force pairs.

So, the explanation for action-reaction forces—the fact that you feel resistance when pushing and the wall pushes back with equal force—is Newton's Third Law.