btw / about gravity

Gravitation is a natural phenomenon by which all objects with mass attract each other, and is one of the fundamental forces of physics. In everyday life, gravitation is most commonly thought of as the agency that gives objects weight. 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 convection (by which hot fluids rise); for heating the interiors of forming stars and planets to very high temperatures; and for various other phenomena that we observe. Gravitation is also the reason for the very existence of the Earth, the Sun, and most macroscopic objects in the universe; without it, matter would not have coalesced into these large masses and life, as we know it, would not exist.

Modern physics describes gravitation using the general theory of relativity, but the much simpler Newton's law of universal gravitation provides an excellent approximation in most cases.

The terms gravitation and gravity are mostly interchangeable in everyday use, but in scientific usage a distinction may be made. "Gravitation" is a general term describing the attractive influence that all objects with mass exert on each other, while "gravity" specifically refers to a force that is supposed in some theories (such as Newton's) to be the cause of this attraction. By contrast, in general relativity gravitation is due to spacetime curvatures that cause inertially moving objects to accelerate towards each other.

http://en.wikipedia.org/wiki/Gravity