Newton's law of universal gravitation
for 2
point masses or
2
spherically symmetric bodies
in magntitude form (i.e., just the magnitude of the equal and opposite forces between two bodies):
F is size of the pulling gravitational force
each object exerts on the other,
gravitational constant G
=
6.67430(15) × 10-11
in MKS units,
mass 1 times mass 2
is the product of the object
masses,
and r is their separation for point masses
or their
center-to-center separation for
spherically symmetric bodies.
Note, point masses do not exist, and so gravitational force never goes to infinity.
In fact, inside finite bodies the self-gravity gravitational field always goes to zero somewhere which
for spherically symmetric bodies is the center.
(This short insert is from
Mechanics file:
newtonian_physics_grav_law.html.)