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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?

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The first thing that comes to mind is that waste disposal should be easy. Of course, any beings on the outside of and in the vicinity of the sphere are not likely to appreciate this one bit. – Alfred Centauri Jul 16 '12 at 23:33
"Also, with sufficient mass in its shell, what is the effect of (real) gravity on objects on the inner surface?" If you have a uniform spherical shell there is no effect at any mass. – dmckee Jul 16 '12 at 23:41
Also, this has been in---sometimes very well---in SF over and over again. You should read some of the existing literature or you will come off as either ignorant or pretentious. Seriously. People have been writing in these settings for more than fifty years. – dmckee Jul 16 '12 at 23:43
Finally, I see this as a "make-a-list" question which would make it unsuitable for the site. You might try chat, but ours has a pretty low activity so you might get a better response on the SciFi.Se chat which is sometimes quite jumping with activity. – dmckee Jul 16 '12 at 23:51
Advice well taken, dmckee. I am aware of Ringworld and Rendezvous with Rama and am looking for stories that feature a sphere instead of other geometrical shapes. I also would like to focus on the physics and not have to wade through story, though I have no doubt that it's going to be enjoyable. – Jonas Arcangel Jul 16 '12 at 23:56

One issue is since it's a sphere, the spinning is only like gravity along the plane of spin. At the poles, there will be no such effect, and part-way to the poles, the force will be less, and at an angle to the surface. That's why a hollow "ringworld" is slightly more plausible than a hollow sphereworld. This would be a welcome question with attempted-if-less-knowledgeable answers on

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You can describe Coriolis effect

If one walks along meridian, strange force pulls him aside.

If one walks along parallel, gravity appears stronger or weaker.

If one jumps, he lands into different place.

All these effects the grater the faster planet rotation. If it rotates to make Earth-like weights, effects will be noticeable.

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