The exact same principles of physics are involved regardless of the medium through which an object is falling.
That said, which particular principles are having the most effect may change. In air, for example, drag matters more than buoyancy for most solid objects, but in water this can be reversed, at least for objects that have any significant buoyancy to begin with.
No matter how you slice it, however, the same principles apply in all cases where terminal velocity applies, i.e. not in empty space.
