Is this calculus correct, or do the decimals points have to be converted ? Thanks so much , cause I'm stuck The gravitational constant is 6.673 * 10 to the -11th power. The radius of the moon is 1737400 meters. Its mass (which is independent of gravity) is 7.35 * 10 to the 22nd power kg. Now, given that F=ma and F=GmM/r squared, we can set a = GM/r squared. So: a = (6.67300f * (Math.Pow(10, -11)) * 7.36f * Math.Pow(10, 22))/(1737400f*1737400f) Running this I get a = 1.62704402190015. Now, since F (the force of gravity) = ma, then for the same object, F1/F2 = ma1/ma2. This means that the ratio of the forces is equal to the ratio of accelerations since the m cancels out: F1/F2 = a1/a2. Finally, we take acceleration on the earth, which is roughly 9.8m/s/s. Dividing our calculated value for a by that, we get: 1.62704402190015 / 9.8 = 6.02319 And there it is, our 1:6 ratio.