text: how did earth gain gravitational force? does the amount of gravity of each planet vary depending on it's size? when we r in moon, our weight decreases. so, when we go to jupiter does our weight increase? yes and no. the gravitational force is given in g = gm / r^2, where g = 6.67*10^-11, m = mass of planet, and r = radius in metres. so the g increases if the mass increases, or the radius decreases. if the moon had the same mass as us, you would weight a lot heavier on it than on earth. but since it is a lot lighter than smaller than us, the g on the surface of the moon is less than that of ours, and since weight = mass x gravity, you weigh less.