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Astro*Dictionary by Michael Erlewine





1 article for "Gravitation"

Gravitation [Astro*Index]

(Physics) The 'force' or 'action at a distance' manifested by the acceleration (toward each other) of two free material particles or bodies, or of radiant- energy quanta. This term derives its meaning from two formulae of Newton's Theory of Gravitation:
                          F=ma             and             F=Gm1m2r/r3

Many texts refer to Newton's Law of Gravitation, but it remains just a theory, in spite of its successful application in many areas. According to Einstein's Theory of Relativity, it is improper to refer to this effect as a force; rather, the effect is explained as a tensor. In the Einstein viewpoint, the motion of the planets is explained by a distortion of the space-time continuum in the vicinity of a large mass (the Sun); but the planets continue to follow Geodesic Paths, and are, therefore, not attracted by outside forces (in particular by any kind of gravitational 'force'). Computationally, the motion of the planets is predicted by using the Newtonian formulae, with Relativity applied as a 'correction'. This approach has permitted astronomers to predict the motion of Mercury with greater accuracy: Mercury's perihelion advances at the rate of 574" per century, which is 43" faster than it should according to Newton's theory.

See also:
♦ Perihelion ♦ Newton


Astro*Index Copyright © 1997 Michael Erlewine