first law of motion

noun Physics.
See under law of motion.
Dictionary.com Unabridged

law of motion

noun Physics.
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)
Also called Newton's law of motion.


Origin:
1660–70

Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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Example sentences
Newton's first law of motion is exhibited by the pendulum, albeit with the effects of the second law and his law of gravitation.
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