Newton's Laws of Motion (redirected from Weak form of Newton's Third Law)

Newton's laws of motion: see motion.

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Newton's laws of motion

Relations between the forces acting on a body and the motion of the body, formulated by Isaac Newton. The laws describe only the motion of a body as a whole and are valid only for motions relative to a reference frame. Usually, the reference frame is the Earth. The first law, also called the law of inertia, states that if a body is at rest or moving at constant speed in a straight line, it will continue to do so unless it is acted upon by a force. The second law states that the force F acting on a body is equal to the mass m of the body times its acceleration a, or F = ma. The third law, also called the action-reaction law, states that the actions of two bodies on each other are always equal in magnitude and opposite in direction.

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Newton's laws of motion [′nüt·ənz ′lȯz əv ′mō·shən]

(mechanics)

Three fundamental principles (called Newton's first, second, and third laws) which form the basis of classical, or Newtonian, mechanics, and have proved valid for all mechanical problems not involving speeds comparable with the speed of light and not involving atomic or subatomic particles.

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Newton's laws of motion

Three fundamental principles which form the basis of classical, or newtonian, mechanics. They are stated as follows:

First law: A particle not subjected to external forces remains at rest or moves with constant speed in a straight line.

Second law: The acceleration of a particle is directly proportional to the resultant external force acting on the particle and is inversely proportional to the mass of the particle.

Third law: If two particles interact, the force exerted by the first particle on the second particle (called the action force) is equal in magnitude and opposite in direction to the force exerted by the second particle on the first particle (called the reaction force).

The newtonian laws have proved valid for all mechanical problems not involving speeds comparable with the speed of light and not involving atomic or subatomic particles. See Dynamics, Force, Kinetics (classical mechanics)

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Newton’s Laws of Motion 

three laws that form the foundation of classical mechanics. They were formulated by I. Newton in 1687. The first law is: “Every body continues its state of rest or uniform motion in a straight line, except insofar as it is compelled to change that state by an external impressed force.” The second law is: “The rate of change of linear momentum is proportional to the impressed force and takes place in the direction of the straight line along which the force acts.” The third law is: “To every action there is an equal and opposite reaction, or, in other words, the mutual actions between any two bodies are always equal and act in opposite directions.”

Newton’s laws of motion followed from a generalization of numerous observations, experiments, and theoretical investigations conducted by Galileo, C. Huygens, Newton himself, and others.

According to modern concepts and terminology, in the first and second laws the term “body” should be understood to mean a mass point, and “motion” to mean motion with respect to an inertial frame of reference. The mathematical expression of the second law in classical mechanics has the form d(mv)/dt = F, or mw = F, where m is the mass, ν the velocity, and w the acceleration of the point, and F is the impressed force.

Newton’s laws of motion cease to be valid for objects of very small dimensions (elementary particles) and for velocities close to the velocity of light.

REFERENCES

Galilei, G. “Besedy i matematicheskie dokazatel’stva, kasaiushchiesia dvukh novykh otraslei nauki, otnosiashchikhsia k mekhanike i mestnomu dvizheniiu.” Soch., vol. 1. Moscow-Leningrad, 1934. (Translated from Latin.)
Newton, I. “Matematicheskie nachala natural’noi filosofii.” In A. N. Krylov, Sobr. trudov, vol. 7. Moscow-Leningrad, 1936. (Translated from Latin.)
See also references under MECHANICS.

S. M. TARG