It is the attractive force existing between any two
particles of matter. Because this force acts throughout
the universe, it is often called universal gravitation.
Isaac Newton was the first to recognize that the force
holding any object to the earth is the same as the
force holding the moon and planets in their orbits.
According to Newton's law of universal gravitation,
the force between any two bodies is directly proportional
to the product of their masses and inversely proportional
to the square of the distance between them. The constant
of proportionality is known as the gravitational constant
(symbol G) and equals 6.670 x 10-11
newton-m2/kg2
in the MKS system of units. The measure of
the force of gravitation on a given body on earth
is the weight of that body.
In the general theory
of Relativity, gravitation is explained geometrically
matter in its immediate neighbourhood causes the curvature
of the four dimensional Space-time continuum.
