Britannica Sources used in this answer

Why do action and reaction forces not cancel each other on a single object?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Title page of Isaac Newton's Philosophiae Naturalis Principia Mathematica, 1687, featuring large Latin text and publication details in a bordered layout. — Newton’s laws of motion The title page of Isaac Newton's *Philosophiae Naturalis Principia Mathematica* (1687; *Mathematical Principles of Natural Philosophy*), the work in which the physicist introduced his three laws of motion.

Action and reaction forces do not cancel each other out on a single object because they never act on the same body. According to Newton’s third law of motion, when two bodies interact, they exert equal and opposite forces upon each other, with each force acting on a different object.1

For example, when an object rests on a table, the downward force of gravity acting on the object and the upward force exerted by the table on the object are equal and opposite, but they act on the same body; therefore, they balance each other to produce equilibrium. In contrast, the action-reaction pair consists of the object pushing down on the table and the table pushing up on the object. Because these two forces act on different bodies—one on the table and one on the object—they cannot cancel each other out.1