I'm writing a short story set in an artificial planet-sized sphere with an ecosystem in its inner surface, whose "gravity" is created through spinning.
Energy sources aside, what other interesting physical characteristics should I take into consideration, apart from varying force levels as one moves relative to the direction of the spin (may be minute given the size of the structure), as well as increasing "weightlessness" as one gets closer to the axis?
Also, with sufficient mass in its shell, what is the effect of (real) gravity on objects on the inner surface?