THE SPINNING SHIP PROBLEM:
The 3 problems I saw mentioned here about using rotational inertia to replace gravity were:
1. movements of astronauts *inside* would "distabilize" the ship and cause it to stop rotating properly
2. as humans arenīt a point object as high school physics would like us to believe
a thing called the Corelious force develops when you rotate them on the inside of a wheel like structure of a radious not big enough compared to the size of the person inside.
3. even though inertia gives us 1 g and minimum corelious force we still experience muscle atrophy and "back stress"
My thoughts on these:
1. If we look closely at Newtons laws of motion we see that every action as a reaction... so what could be the "worst" disturbance an astronaut could cause to a rotating wheel? The absolute worst would be for him to run in the same direction the wheel is spinning... that way his legs would push the wheel in the opposite direction on the spinning motion and tend to slow it down... but the funny thing is that the moment this astronaut stopped running the wheel would start spinning at the same speed as it did in the beginning because there is a little thing called rotational inertia conservation which states that in any inclosed system (a spaceship and its occupats) the rotational inertia of the whole system cannot be changed by internal forces of the system... you can bounce all you want inside but you wonīt change anything.
2. The obvious solution to this issue is to build a wheel that has a radious more than 100x the normal height of a person (heeh... big, yes... very big) althugh this might be impractical and almost impossible to do now it might be in the future... but sadly its the only solution physics offers us for now...
3. Iīm pretty sure this is the result of insufficient inertia and persisting differential (Corelious) forces in a wheel not big enough or not spinning fast enough. Because if we had a big wheel with almost no differential forces and a g inertial acceleration at the ouer rim... we wouldīt be able to set it apart from normal gravity. (itīs not only simulated... itīs exactly the same as normal gravity in all itīs affects... you just have to have a wheel big enough to eliminate the differential forces)