Variable gravitational acceleration

[niteman555]

If there are two massive bodies in an isolated space, how does one derive the formula describing their motion, in other words, how do I combine the gravitational field and kinematic equations into one?

 

[piyushkumar]

one can do it with calculus.
write the force equation as m1$\frac{dv1}{dt}$=$\frac{G m1 m2}{r*r}$, where r is distance b/w them. Similarly for m2