law of motion

American  

[law uhv moh-shuhn] / ˈlɔ əv ˈmoʊ ʃən /

noun

Physics.

1. any of three laws of classical mechanics, either the law that a body remains at rest or in motion with a constant velocity unless an external force acts on the body first law of motion, the law that the sum of the forces acting on a body is equal to the product of the mass of the body and the acceleration produced by the forces, with motion in the direction of the resultant of the forces second law of motion, or the law that for every force acting on a body, the body exerts a force having equal magnitude and the opposite direction along the same line of action as the original force third law of motion, or law of action and reaction.

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Etymology

Origin of law of motion

First recorded in 1660–70

Example Sentences

The fundamental law of motion of cybernetics is that if you have a control system, it has to have at least as much complexity as the thing it's trying to control.

From Salon • Apr. 26, 2025

This is consistent with Aristotle’s debunked theory of physics, which did not account for the effects of Newton’s first law of motion.

From Scientific American • Jul. 21, 2023

No amount of word salad can repeal Isaac Newton’s second law of motion, F=ma.

From Washington Post • Feb. 16, 2023

Seale and Miller defy Issac Newton’s first law of motion: A body at rest will stay at rest.

From Seattle Times • Aug. 23, 2022

This principle is Newton’s very first law of motion and was considered old news even in Miss Penelope Lumley’s day.

From "The Incorrigible Children of Ashton Place: Book I: The Mysterious Howling" by Maryrose Wood