I might not be able to give a super coherent picture but I will have a go. The force that hold nuclei together is based on the residual strong force, it is a complex system so the models used for it tend to be semi-empirical (yukawa or reid potential). They go from being repulsive at short distances to being attractive with something like an exponential decay as you go further away. The force is very strong at 1 femtometre and pretty much negligible 3 femtometres away. This is only the residual of the strong force though, which is what you can think of as holding quarks together. This force is very strange in that it doesn't get weaker the further the quarks get apart, but if it gets far enough then the energy will create new particles. That's just the strong force, I will leave it to someone more knowledgeable than me to try to explain the weak force.

For a point or ball, the formula is F=A/r^2

For a complicated shape, the formula is (something like[1]) F=A/r^2+B/r^3+C/r^4+... , where r is the distance to the "center" (and some parts are closer and some parts are more far away).

An important property of magnets is that A=0, so the r^2 term dissapears. And in many cases it can be simplified to F=B/r^3 [1, again].

[1] The complete formula considers also the directions, so it's longer https://en.wikipedia.org/wiki/Multipole_expansion

weak and strong forces are mediated by particles that have mass and therefore their force falls off basically exponentially, as exp(-m*r) it's not really the same as decaying in extra dimensions, because in that case the force law would look something like 1/r^(n-1)