Newton's Third Law Force Pairs · PhysicsBowl 2011 #13
Physics · mechanics
Problem
A physics book sits at rest on a table. On top of the book is a calculator, also at rest. Which one of the following choices is the Newton's Third Law pair force to the force that the table exerts on the book? (A) The contact force on the table by the book. (B) The gravitational force on the book by the Earth. (C) The gravitational force on the combination of the book and calculator by the Earth. (D) The contact force on the book by the calculator. (E) The contact force on the table by the ground supporting it.Intuitive explanation
Newton's Third Law pairs are action–reaction forces between the same two objects: they're equal in magnitude, opposite in direction, and act on different bodies. The table pushes up on the book with a normal force; its Third Law pair must be the book pushing back on the table with equal force. The key is identifying which force involves the same two interacting objects (table and book) but reversed roles.
Intuitive explanation
Newton's Third Law pairs are action–reaction forces between the same two objects: they're equal in magnitude, opposite in direction, and act on different bodies. The table pushes up on the book with a normal force; its Third Law pair must be the book pushing back on the table with equal force. The key is identifying which force involves the same two interacting objects (table and book) but reversed roles.