What is an action-reaction pair?

• A. A single force acting on an object
• B. Two forces that are identical in size
• C. Two forces that are equal in size but opposite in direction
• D. A force that acts on a stationary object

Answer: (C)

An action-reaction pair consists of two forces that are equal in size but opposite in direction, as described by Newton's Third Law of Motion. This principle states that for every action, there is an equal and opposite reaction. When one object exerts a force on a second object, the second object exerts a force back on the first object that is equal in magnitude and opposite in direction. This interaction is fundamental to understanding how forces work in pairs, allowing objects to move in response to each other's actions.

For instance, when you push against a wall, your hand applies a force to the wall (the action), and the wall applies an equal force back to your hand (the reaction). This dynamic is essential for analyzing motion and force interactions in various physical situations, whether they involve contact forces, like friction, or non-contact forces, like gravitational or magnetic forces.