I read a lot of sci-fi, and simulated gravity is a frequent feature of space sci-fi. I am interested in real physics, not hand-wavy magic artificial gravity. In the Expanse, highly efficient nuclear rockets create the experience of gravity by way of constant acceleration. This is easy for me to understand – on the vessel, the deck you are standing on is accelerating and pushing against your feet.
What I do not under is how centrifugal force acts in a way similar to gravity. I have a scenario in my imagination that illustrates my confusion. I imagine that a torus-shaped station in space has stopped rotating and everyone evacuated. A repair person in a space suit has floated into the station to repair it. He or she travels in microgravity in a space between the inner walls and outer walls of the station, almost like someone floating inside of a holo donut. While inside the immobile torus, and suspended between the walls in such a way that he or she isn’t touching either the innermost or outermost walls of the donut, s/he completes the repair needed to spin up the station again.
What happens next? The sci-fi I have read would lead me to believe that as the torus begins to spin up, the repair person will experience an effect similar to gravity and will coast toward the outermost wall until the inside of that wall becomes like a floor to them. If that is true, why? I would think that a person suspended within the boundaries of a torus would continue to float while the innermost and outermost walls in front of and behind them spun in their cycle. I don’t get why this spinning will make the repair person drift to one side and create a “down” to their perspective. Can anyone enlighten me?
Tl;dr: centrifugal force confuses me, and I don’t know why it works in microgravity(or just fundamentally misunderstand it)
In: Physics
If the area the person is floating in is a vacuum, you’re right, they would “stay still” while the station rotated around them. If there was still air in the station, however, when it started to spin, friction or internal walls would cause the air within to start moving with it. The air would blow on the repair person, which would eventually make them start to move slightly along with the air. But since objects like to move in straight lines, and the inside of the station is round, the repair person will eventually bump into the outer wall. (the direction the “wind” pushes them in will change when they’re in different parts of the ring, but it will never directly push them towards or away from the wall).
If the wall drags them along, they will continue to speed up along with it. But, since they constantly “want” to move in a straight line and the wall is curved, they’ll find themselves being pressed against the wall. If the station is spinning fast enough, they’ll be able to stand “up” on the wall, using their legs to support themselves against it. Their legs would be pushing the rest of their body as well, which would feel (about) the same as standing on a stationary surface in a gravitational field.
There isn’t actually any field pushing objects inside the torus. Things are just spinning along with the ring and colliding with the outer wall because the wall isn’t straight. But if the ring is large enough, and everything inside the ring is spinning with it, the differences between that and “real” gravity for someone on the outer wall are very hard to detect.
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