Newton's laws of motion
Also found in: Dictionary, Thesaurus, Medical, Legal, Wikipedia.
Types of Motion
The Laws of Motion and Relativity
The relationship between force and motion was expressed by Sir Isaac Newton in his three laws of motion: (1) a body at rest tends to remain at rest or a body in motion tends to remain in motion at a constant speed in a straight line unless acted on by an outside force, i.e., if the net unbalanced force is zero, then the acceleration is zero; (2) the acceleration a of a mass m by an unbalanced force F is directly proportional to the force and inversely proportional to the mass, or a = F/m; (3) for every action there is an equal and opposite reaction. The third law implies that the total momentum of a system of bodies not acted on by an external force remains constant (see conservation laws, in physics). Newton's laws of motion, together with his law of gravitation, provide a satisfactory basis for the explanation of motion of everyday macroscopic objects under everyday conditions. However, when applied to extremely high speeds or extremely small objects, Newton's laws break down.
Motion at speeds approaching the speed of light must be described by the theory of relativity. The equations derived from the theory of relativity reduce to Newton's when the speed of the object being described is very small compared to that of light. When the motions of extremely small objects (atoms and elementary particles) are described, the wavelike properties of matter must be taken into account (see quantum theory). The theory of relativity also resolves the question of absolute motion. When one speaks of an object as being in motion, such motion is usually in reference to another object which is considered at rest. Although a person sitting in a car is at rest with respect to the car, both in motion with respect to the earth, and the earth is in motion with respect to the sun and the center of the galaxy. All these motions are relative.
It was once thought that there existed a light-carrying medium, known as the luminiferous ether, which was in a state of absolute rest. Any object in motion with respect to this hypothetical frame of reference would be in absolute motion. The theory of relativity showed, however, that no such medium was necessary and that all motion could be treated as relative.
See J. C. Maxwell, Matter and Motion (1877, repr. 1952).
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)
Newton's laws of motionThe three fundamental laws concerning the motion of bodies that were formulated by Isaac Newton and published together with the law of gravitation in Principia, 1687. The laws are
The first law was conceived by Galileo, who first realized the falsity of the Greek notion that a force is required to maintain a body in motion. Newton's laws of motion and of gravitation are fundamental to celestial mechanics.
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.
REFERENCESGalilei, 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