In sci-fi with “spinning” ships to make gravity, how does someone drop something and it lands at their feet?

Question

This fogs my brain every time I watch one of these shows and I feel like maybe I’m completely misunderstanding the physics.

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You’re in a “ring” ship. The ring spins. You’re standing on the inside of the ring so it takes you along with it, and the force created “pins” you to the floor, like a carnival ride. Ok, fine.

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But that’s not gravity, and it’s not “down”. Gravity is acceleration, so what keeps the acceleration going in the ring ship is that you are constantly changing your angular momentum because you’re going in a circle. Ok, so when you let go of something, like a cup or a book, wouldn’t it go flying towards the floor at an angle? If you jumped wouldn’t you look like you rotated a little before you hit the ground, because you’d, for that moment, be continuing the momentum of your angular velocity from when you left the floor and the room would continue on it’s new, ever turning, course?

Wouldn’t it kind of feel like walking “uphill” one direction and “downhill” the other, with things sliding about as the room “changed” direction constantly?

Am I just COMPLETELY missing this idea and creating a cause and effect that doesn’t exist?

In: Physics

Answer 1

The big issue here is the *radius* of the ring. If it is too small, then not only will dropped objects curve away, but walking around the thing will be next to impossible without throwing up or falling over. There will be a very noticeable gravity gradient between your feet and your head.

If the ring is big enough, these effects will be too slight to notice, and a dropped object will fall in what *appears to be* a reasonably straight line in your frame of reference. Measure it with a laser or something, you can maybe see a slight curve. It would take a radius of at least 100 meters for humans to effectively walk around inside it with no ill effects.

And another thing about SF spaceships: they frequently show a [ship that has a rotating part and a stationary part.](https://www.sharecg.com/images/original/164592.jpg) This will not work, at least not without constantly expending energy. The reason is because the “stationary” part is not anchored to anything, so it will just counter-rotate (same thing that happens to a helicopter if it loses its tail rotor).