I was thinking about Newton's gravity equation: F = G * m(1) *m(2) / r^2. I wanted to find the acceleartion due to gravitational attraction that would occur between two objects of different masses so I used the equation F=ma. Then I ran into difficulty: should I use the sum of the masses to solve this or should I use both masses individually. In other words should my acceleration equation be a= F / m(1) + F / m(2) OR a = F / [m(1)+m(2)] ?????? Which one is correct, if any? Clearly the two are not equal (if m(1) is 4 and m(2) is 3 then by the first equation the acceleration will be F/4 + F/3 which is 7F/12 and by the second equation the acceleration is F/7). Another problem is that these equations would allow heavier things to fall faster to the Earth (though only significantly on a large scale). That is, the moon would fall faster toward the Earth than would a car because the change in the force would exede the change in the mass. I would appreciate any help on the matter.