## Gravitational Field Strength

Gravity is always attractive. Any two particles with mass attract each other. Antimatter has mass just like ordinary matter, and all gravitational forces between all matter and antimatter particles is attractive.<br />
The strength of a gravitational field - also called the acceleration due to gravity - is the force per unit mass. Newton's Law of Universal Gravitation states that the force between point masses of mass
$m_1, \: m_2$
respectively separated by a distance
$r$
is
$F=\frac{Gm_1m_2}{r^2}$
.
(
$G=6.67 \times 10^{-11} m^3/kg/s^2$
is the universal gravitational constant and is often called big G)
Hence the gravitational field strength at the position of mass
$m_1$
due to the mass
$m_2$
is
$\frac{F}{m_1}=\frac{Gm_2}{r^2}$
and the gravitational field strength at the position of
$m_2$
due to the presence of mass
$m_1$
is
$\frac{F}{m_2}=\frac{Gm_1}{r^2}$
.
The gravitational field strength is given the label
$g$
at is actually equal to the acceleration of the body.
The acvereration due to gravity on the Earth is
$g=\frac{GM_{EARTH}}{R^2_{EARTH}}=9.8m/s^2$