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My explorers will be using a torsion balance to weigh their new planet. Is there a way to also use a torsion beam to determine the direction to the poles of a rotating planet?

My assumption is that it could because the two attracting weights have three forces acting on them, and when the beam is aligned latitudinally, the force vector from centrifugal acceleration is working in opposite angles on the two weights relative to the beam center, except at the equator and the poles. The beam aligned longitudinally will always have exactly the same centrifugal force vector on them, except at the poles where they would be opposite. And if the weights are aligned vertically, they have different angular velocities. It would seem that in some arrangement or combination, the difference between the centrifugal force vector could be used to indicate the planet's axis of rotation and thereby point to the poles.

Torsion Balance force vectors

I am not interested in alternatives to a torsion balance. Please let me know if there is some test or series of tests which can be done with a torsion balance that would indicate the direction to the poles of a rotating planet.

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    $\begingroup$ This sounds like more of a physics question than a question about building your fictional world. $\endgroup$
    – sphennings
    Aug 15 '20 at 1:28
  • $\begingroup$ I think any hard science question will fit another exchange, but because the planet in question is fictional and part of a fictional world, I feel it doesn’t fit the physics forum. If I was asking about Earth or another true body, that makes more sense. $\endgroup$
    – Vogon Poet
    Aug 15 '20 at 1:37
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    $\begingroup$ As long as you can see the stars at night, and map their arcs across the sky as the world turns, and know the planet is spherical, and its radius, working out where the poles are is doable with basic trigonometry. $\endgroup$
    – notovny
    Aug 15 '20 at 1:56
  • $\begingroup$ I’m voting to close this question because it belongs on physics.stackexchange.com since its asking about the basic measurement of forces using standard instruments $\endgroup$
    – EDL
    Aug 15 '20 at 2:04
  • $\begingroup$ Real world questions are on-topic so long as they are asked in a worldbuilding context - which this question is. However, the four stream-of-consciousness questions don't make for a high-quality question. Please remember, Vogon, that SE's model is one-specific-question/one-best-answer. Try to keep things focused. Thanks. $\endgroup$ Aug 15 '20 at 3:42
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No. A torsion balance is entirely the wrong tool for that purpose.

A simple stick in the ground will suffice. Or, if for some reason tracking shadows isn't your thing, a gyrocompass will do it.

Incidentally, even if a planet has a magnetic field, there is no guarantee that a magnetic compass will point reasonably close to the rotational poles like they do on Earth.

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    $\begingroup$ Technically this doesn't meet the hard-science mandate because it doesn't explain with the appropriate citations, etc., why "no" is the best answer. Can you explain why the torsion balance is "entirely the wrong tool for that purpose"? $\endgroup$ Aug 15 '20 at 3:43
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    $\begingroup$ Incidentally, even if a planet has a magnetic field, there is no guarantee that a magnetic compass will point reasonably close to the rotational poles like they do on Earth. In fact I believe Earth is the only planet with a magnetic field so far with the magnetic poles close to the geographical ones. The gas giants don't even seem to have their magnetic axes intersecting their rotational axes at all. Adding this to the answer could make it more in line with hard-science :) $\endgroup$ Aug 17 '20 at 0:49

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