One of four fundamental forces of nature is gravity. It's weakest force of all and always is attractive. Gravtiation force is proportional to body masses and inversly proportional to the square distance between them. From a cosmological perspective, gravitation causes dispersed matter to coalesce, and coalesced matter to remain intact, thus accounting for the existence of planets, stars, galaxies and most of the macroscopic objects in the universe. It is responsible for keeping the Earth and the other planets in their orbits around the Sun; for keeping the Moon in its orbit around the Earth; for the formation of tides; for natural convection, by which fluid flow occurs under the influence of a density gradient and gravity; for heating the interiors of forming stars and planets to very high temperatures; and for various other phenomena observed on Earth and throughout the universe.
This clip is taken from the NOVA PBS series "THE ELEGANT UNIVERSE' and is used under the provisions of the Digital Millineum Copyright Act of 1998 (Title IV).
Brian Greene guides us through Newton's discovery of gravity to the explanation of it, through Einsteins Theory of Relativity.
Brian Greene is a theoretical physicist and one of the best-known string theorists. Since 1996 he has been a professor at Columbia University.
The Elegant Universe was adapted for a three hour program in three parts for television broadcast in late 2003 on the PBS series NOVA.
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