2.3.A.1Concept
Newton's third law describes the interaction of two objects or systems in terms of the paired forces that each exerts on the other.
ExampleFinding the real third-law pair for a resting book1 / 3
A book rests on a table, held up by the normal force and pulled down by gravity. Identify the genuine Newton's third-law pair in this situation, and explain why gravity and the normal force (both acting on the book) are NOT that pair.
Try it on paper first, then reveal each step to check your work.
Step 1 — Check what a third-law pair requires
A Newton's third-law pair always involves exactly two different objects, each exerting a force on the other.