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Dynamics

proportionality constant, net force, general theory of relativity, gravitational attraction, gravitational field

Newton’s second law relates net force and acceleration. A net force on an object will accelerate it—that is, change its velocity. The acceleration will be proportional to the magnitude of the force and in the same direction as the force. The proportionality constant is the mass, m, of the object. F = maIn the International System of Units (also known as SI, after the initials of Systeme International), acceleration, a, is measured in meters per second per second. Mass is measured in kilograms; force, F, in newtons. A newton is defined as the force necessary to impart to a mass of 1 kg an acceleration of 1 m/sec/sec; this is equivalent to about 0.2248 lb.

A massive object will require a greater force for a given acceleration than a small, light object. What is remarkable is that mass, which is a measure of the inertia of an object (inertia is its reluctance to change velocity), is also a measure of the gravitational attraction that the object exerts on other objects. It is surprising and profound that the inertial property and the gravitational property are determined by the same thing. The implication of this phenomenon is that it is impossible to distinguish at a point whether the point is in a gravitational field or in an accelerated frame of reference. Einstein made this one of the cornerstones of his general theory of relativity, which is the currently accepted theory of gravitation.



Article key phrases:

proportionality constant, net force, general theory of relativity, gravitational attraction, gravitational field, newtons, International System of Units, cornerstones, Einstein, implication, reluctance, kilograms, velocity, magnitude, phenomenon, acceleration, SI, kg, Mass, direction, meters, measure, object, objects, thing, point, law, maIn

 
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