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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> By definition, a spinning object is under acceleration… And force requires energy, so why doesn’t the spinning of an object expend its angular momentum and slow it down over time?
Force does not require energy.
Forces do work on something (or objects do work against a force) when the thing moves **in the direction of** (or away from) **the force**.
If you slide something across your desk the force of gravity is pulling that thing down, but you aren’t doing any work against gravity because the weight is pulling the object down, while you are moving it sideways.
The key thing about (stable) circular motion is that while everything is being accelerated inwards, it is only moving in the circular direction, so no work is done by or against the force; the motion is always at right angles.
With non-circular angular motion (so ellipses etc.) work is done by and against the force, but it cancels out; as the thing gets closer to the centre of rotation work is done by the force on the object – it gains energy (usually speeding up). But as it moves back away work is done against the force – it loses energy (usually slowing down).
Does that help with your questions?
If not, feel free to ask for more details.
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