Important Equations

m2  =  mass 2  

m1 = mass 1 

M = mass of the planet 

g  =  acceleration due to gravity 

F1 = The force  m1 feels from m

F2 = The force  m2 feels from m

G = Gravitational constant 

G6.67300 × 10-11 m3 kg-1 s-2 

r = distance between m1 and m2  

Newton's law of universal gravitation is about the universality of gravity.  ALL objects attract each other with a force of gravitational attraction. Gravity is universal. This force of gravitational attraction is directly dependent upon the masses of both objects and inversely proportional to the square of the distance which separates their centers.

Definition provided by physics classroom 

Newton's Law of Universal Gravity