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The constant of proportionality is called , the gravitational constant, the universal gravitational constant, or Newton's constant. The gravitational constant is a fundamental physical constant which appears in Newton's law of universal gravitation and in Einstein's theory of general relativity.
In SI units, the 2002 CODATA recommended value of the gravitational constant is
Another authoritative estimate is given by the International Astronomical Union (see Standish, 1995).
The gravitational force is relatively weak. As an example, two SUVs, each with a mass of 3000 kilograms and placed with their centers of gravity 3 metreFor other uses of "metre" and "meter", see Metre (disambiguation). The metre is the basic unit of length in the International System of Units (SI: Systeme International d'Unites). It is defined as the length of the path travelled by light in absolute vacus apart, will attract each other with a force of about 67 micronewtons. This force is approximately equal to the weightFor the 1994 album by the group Rollins Band, see Weight (album). Weight is the force exerted upon an object by virtue of its position in a gravitational field. In a constant gravitational field, such as the Earth's, this force is proportional to the obje of a large grain of sand.
The accuracy of the measured value of has increased only modestly since the original experiment of Cavendish.
is quite difficult to measure, as gravity is much weaker than other fundamental forces, and an experimental apparatus cannot be separated from the gravitational influence of other bodies. Furthermore, gravity has no established relation to other fundamental forces, so it does not appear possible to measure it indirectly. A recent review (Gillies, 1997) shows that published values of have varied rather broadly, and some recent measurements of high precision are, in fact, mutually exclusive.