math issue

i think i found a way to fix it…

since the v=sqrt(GM/r) equation is just finding the square root of the gravity acceleration (GM/r), then i could use earth’s gravity (in game, it’s 1,000…unit is unkown) and then divide that by an unknown number (closest i got was 102) to get 9.8, that way, since i know it works for earth, it must work for any celestial object

and, i assume you know how it falls together

@SamTheFox I'm not quite sure what you are asking for. If the moon's radius is 2.38 meters... then unless it's density is up there with neutron stars, it's gravity will be negligible. That said... if you want to have low-mass objects with unrealistic gravity, you could always change the gravitational constant (i.e. G =/= 6.6743x10^-11 m^3kg^-1s^-2).

But if you meant you just want to calculate the mass for a realistic planetoid, without having it's density - your best bet is to just use a 'reasonable guess' based on real-life examples. Mars is about 4 grams per cubic meter, and earth/venus are around 5 grams per cubic meter. So, as an average, let's use 4.5 g/m^3. Multiply that by your volume, and you have the total mass.

EDIT: Wait... I think I just figured out what you were trying to do. I think you're saying that you have a known radius, and a known surface gravity, but unknown mass; correct?
In that case, you don't want sqrt(GM/r), you want F = G(Mm/r^2). Rearrange that to be an acceleration of your observation object: acceleration = GM/r^2
Now, rearrange that to solve for mass: M = acceleration * r^2 / G. Note that "r" here is the radius at which you are observing the gravity, which might not be the surface of the planet. Now that you have a mass for the planet, you can calculate its density by dividing that value by the radius of the planet.

(Note, from the point of view of the gravity formula, all planets are point-masses, i.e. all the mass is located at a infinitely small point in their center. This is sufficient for most use-cases, but it's worth noting that there are some subtle differences if your observing from below the surface of the planet [or even within a planets' atmosphere, if it's a particularly massive/thick one])