Which statement best describes Newton's third law?

• A. Every action is accompanied by an equal and opposite reaction.
• B. Gravity is the only force between objects.
• C. Mass creates momentum without velocity.
• D. Inertia causes an object at rest to remain at rest.

Answer: (A)

Forces come in pairs that oppose each other when two objects interact. This is Newton's third law: the force one object exerts on a second is met with an equal in magnitude, opposite in direction force by the second on the first. These action-reaction forces act on different objects, so they don’t cancel each other out even though they are equal and opposite. A common example is pushing against a wall—the wall pushes back with the same strength in the opposite direction, even though you and the wall are separate objects.

The other statements don’t fit because gravity isn’t the only force between objects; there are many contact forces like friction and normal forces. Momentum is mass times velocity, so mass alone doesn’t create momentum without motion. Inertia is about resisting changes in motion and is described by Newton’s first law, not the action–reaction pairing.