![]() ![]() In Principia Newton stated, ".I have been unable to discover the cause of those properties of gravity from phenomena, and I feign no hypotheses (regarding its mechanism)." Moreover, Newton asserted, "To us it is enough that gravity does really exist, and act according to the laws which we have explained, and abundantly serves to account for the motions of the celestial bodies and our seas." In his later work, Opticks, Newton raised the possibility that the gravitational force might be conveyed through a medium or "ether." Newton admitted having no fundamental explanation for the mechanism of gravity itself. Regardless, the parsimony of Newton's law made its quantitative application easy to translate to problems in astronomy and mechanics. Nearly a century passed, however, before English physicist Henry Cavendish (1731-1810) was to determine the missing gravitational constant ( G) that allowed a reasonably accurate determination of the actual gravitational force. Accordingly, a doubling of one mass resulted in a doubling of the gravitational attraction, while a doubling of the distance between masses resulted in a reduction of the gravitational force to a fourth of its former value. Newton's law of gravitation, mathematically expressed as F = ( G)( m 1 m 2) / r 2, stated that the gravitational attraction between two bodies with masses m 1 and m 2 was directly proportional to the masses of the bodies, and inversely proportional to the square of the distance ( r) between the centers of the masses. The impact of Newton's law of gravity was initially more qualitative than quantitative. Newton extrapolated that the force of gravity (later characterized by the gravitational field) extended to infinity and, in so doing, bound the universe together. Although the force of gravity can become infinitesimally small at increasing distances between bodies, all bodies of mass exert gravitational force on each other. Building on Galileo's observations of falling bodies, Newton asserted that gravity is a universal property of all matter. ![]() Newton's law of universal gravitation was derived from German mathematician and astronomer Johannes Kepler's (1571-1630) laws of planetary motion, the concept of "action-at-a-distance," and Newton's own laws of motion. Moreover, along with Newton's laws of motion, the law of universal gravitation became the guiding model for the future development of physical law. This mathematically elegant law, however, offered a remarkably reasoned and profound insight into the mechanics of the natural world because it revealed a cosmos bound together by the mutual gravitational attraction of its constituent particles. In its simplest form, Newton's law of universal gravitation states that bodies with mass attract each other with a force that varies directly as the product of their masses and inversely as the square of the distance between them. In 1687 English physicist Sir Isaac Newton (1642-1727) published a law of universal gravitation in his important and influential work Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy). Newton's Law of Universal Gravitation Overview ![]()
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