Gravity – All masses of all sizes attract one another and the attractive force is called a gravitational force. It is the gravitational forces between bodies that cause them to come together and coalesce ultimately producing the stars, moons and planets together with smaller celestial bodies. It is the gravitational force that acts between the earth and the sun that counterbalances the centrifugal force resulting from its rotation round the sun that produces a stable celestial system such as the sun and the planets. The term gravity is sometimes used to exclusively describe the attraction of bodies to the earth and is thus strongly associated with the weight of a body.  However, as the earth is not perfectly spherical, although due to a gravitation force, the weight of a body is not constant over the surface of the earth. The general theory of relativity describes gravitation as a natural consequence of spacetime curvature but the simpler explanation given by Newton affords an adequate approximation for most gravitation problems.

Further Information on this Topic can be found in the books of R.P.W. Scott by following the listed links