For masses m and M that are separated by a distance r, the gravitation
force of one mass on the other is:
F_{g}  =  

G is the universal gravitational constant that measures the "strength" of the gravitational interaction: G = 6.67 x 10^{11} N m^{2} / kg^{2}
Important points:
For an object of mass m on the Earth's surface, the gravitational force is:
F_{g}  =  

≡  m g 
This formula defines the gravitational acceleration g.