and 
separated by a distance 
the force 
on mass due to mass is,
is: the law, first formulated by Isaac Newton (1642-1727), which describes the gravitational force between masses. [P3.1]
states: that for two particles of masses and separated by a distance the force on mass due to mass is,
where 
is Newton's universal gravitational constant, and 
is a unit vector pointing from to 
The force is therefore an attractive one, directed along the line joining the masses. [P2.3, P3.3]
Copyright 1997, The Open University