I understand why it needs to exist, otherwise the Earth wouldn’t keep spinning, coins would fall over immediately when you tried spinning them, artificial gravity wouldn’t be possible, etc. But I’m not sure how it works out physically. (nb. I’m talking without regard to drag, friction, etc. For example out in space where those are negligible factors.)
By definition, a spinning object is under acceleration (individual points on the object are constantly turning around the center of rotation, which is a form of acceleration in linear physics). And force requires energy, so why doesn’t the spinning of an object expend its angular momentum and slow it down over time?
Along the same vein, how does artificial gravity work in this context? As I understand it, centrifugal force is a fictitious force, but if I am inside a spinning object I am still being pressed against it as it turns and subjected to acceleration (from an observer’s point of view, at least). And so since I am being accelerated, something has to be using energy to accelerate me, right?
I apologize if I am sounding stupid but this has been wracking my brain for the last while and I’m desperate to figure out the answer. Thank you for any help!
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>And force requires energy
Nope. This is where you’re going wrong and getting confused. A stone can sit on the surface of the earth for decades without requiring any energy input, yet it has an upwards contact force from the ground that’s balancing its weight, keeping it in place.
What requires energy is exerting a force over some distance – i.e. pushing that stone along against friction, or lifting it up against gravity. More specifically, force in the direction parallel to the motion. In circular motion, the force is perpendicular to the direction of motion, so it does not require any energy exertion, and hence things can keep spinning indefinitely if there’s no frictional force or something else slowing them down.
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