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This is part of a conceptual art discussion about various ideas for generation spaceships. I submitted that the only reason I "weigh" 80 kg is because I have the mass of planet Earth the other side of the soles of my shoes. Hypothetically, if another earth came and hovered 100 feet away from my feet, I ought to be equally attracted to both masses and end up floating in air between them--strangely "weightless".

If a cylinder were to be created in space, it might turn or revolve on its central axis, but there's no reason why soil, water, or myself should "stick" to the inner surface. The cylinder would spin while soil, water, and I would float just as we would inside the space station that is currently in orbit around earth.

No matter how big that O'Neill cylinder was, the mass of the opposing sides would cancel each other out unless the floor was earth thickness and the opposing sides were so far away that the attraction felt was negligible--something along the lines of the radius of Earths orbit around the sun perhaps (structural integrity issues aside).

So, my suggestion is that a generational spaceship can be small (and even centrifugal), but for a gravity substitute you'll need metal boots and a magnetic floor (soil and water still float) or a way to attach engines to an Earth-sized object and propel it to escape velocity. (Who can calculate the thrust force required to do that?)

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closed as unclear what you're asking by safesphere, M. Enns, ZeroTheHero, stafusa, Kyle Kanos Jan 11 '18 at 11:12

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  • $\begingroup$ Look up Einstein's principle of equivalence. $\endgroup$ – NickD Jan 11 '18 at 2:00
  • $\begingroup$ Thanks for your valuable input. Without it, generational spaceships would not work as designed and the future of the humanity would be at risk. Please keep working on critical issues the humankind is facing and keep us informed on your future creative ideas. $\endgroup$ – safesphere Jan 11 '18 at 2:17
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    $\begingroup$ Study a few articles on centrifugal force. $\endgroup$ – Hot Licks Jan 11 '18 at 2:55
  • $\begingroup$ what does “generational” refer to in “generational spaceship”? $\endgroup$ – ZeroTheHero Jan 11 '18 at 3:06
  • $\begingroup$ pondering is fun, but physics is hard. should discuss in the chat area. $\endgroup$ – niels nielsen Jan 11 '18 at 3:28
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You are right that any object floating in the middle of a non-spinning cylinder would stay floating just after the cylinder started spinning. None of the floating objects would have any reason to fall to the "ground." However, the air inside the cylinder would start to rotate with the cylinder, starting with the air next to the cylinder surface. The same thing happens if you spin a glass full of liquid; the liquid spins with the glass. This moving air will push on the floating objects and slowly push them to the sides of the cylinder. Once the objects come into contact with the surface, friction will speed them up to the same speed as the spinning cylinder and they will experience artificial gravity.

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