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If so then why? Solid pieces of unsalted whipped butter seem to fall off less often. Sagittarian Milky Way ( talk) 01:06, 15 February 2024 (UTC)
Not homework but I'd like to know how to answer this at the level of an introductory E&M physics class or that sort of thing. Basically a magnetic compass is a magnetized needle with a pivot in the middle, sitting in the Earth's magnetic field. The needle has mass M and length L and I guess we can ignore most subtleties.
My question is, how do you calculate the torque around the pivot, at least dimensionally? My first thought was that it would be quadratic in L (by integrating along the needle) but maybe that's wrong, and I just don't understand magnets well enough.
Oh yes, I guess the needle material itself needs to have some physical magnetization parameters specified. How would I find those, for whatever permanent magnet material is generally used in not-fancy compasses? Do fancy ones use fancier materials like rare earth magnets?
Motivation for asking: if I get a small cheap compass, say 1 inch in diameter, it will tend to get stuck easily, because the torque from the magnet isn't enough to overcome the friction in the pivot. Compasses with better (lower friction) pivots cost more. If I get one of similar quality that's 2 inches diameter, it will have 2x the friction in the pivot (because the needle is twice as heavy) but I wondered if it would have 4x the torque, similar to a moment of intertia calculation. That is, I'm wondering whether big cheap compasses work better than small cheap compasses.
Someday I'll try to work through a textbook on this magnetism stuff. Thanks. 2601:644:8501:AAF0:0:0:0:2F14 ( talk) 03:55, 15 February 2024 (UTC)
Science desk | ||
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< February 14 | << Jan | February | Mar >> | February 16 > |
Welcome to the Wikipedia Science Reference Desk Archives |
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The page you are currently viewing is a transcluded archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages. |
If so then why? Solid pieces of unsalted whipped butter seem to fall off less often. Sagittarian Milky Way ( talk) 01:06, 15 February 2024 (UTC)
Not homework but I'd like to know how to answer this at the level of an introductory E&M physics class or that sort of thing. Basically a magnetic compass is a magnetized needle with a pivot in the middle, sitting in the Earth's magnetic field. The needle has mass M and length L and I guess we can ignore most subtleties.
My question is, how do you calculate the torque around the pivot, at least dimensionally? My first thought was that it would be quadratic in L (by integrating along the needle) but maybe that's wrong, and I just don't understand magnets well enough.
Oh yes, I guess the needle material itself needs to have some physical magnetization parameters specified. How would I find those, for whatever permanent magnet material is generally used in not-fancy compasses? Do fancy ones use fancier materials like rare earth magnets?
Motivation for asking: if I get a small cheap compass, say 1 inch in diameter, it will tend to get stuck easily, because the torque from the magnet isn't enough to overcome the friction in the pivot. Compasses with better (lower friction) pivots cost more. If I get one of similar quality that's 2 inches diameter, it will have 2x the friction in the pivot (because the needle is twice as heavy) but I wondered if it would have 4x the torque, similar to a moment of intertia calculation. That is, I'm wondering whether big cheap compasses work better than small cheap compasses.
Someday I'll try to work through a textbook on this magnetism stuff. Thanks. 2601:644:8501:AAF0:0:0:0:2F14 ( talk) 03:55, 15 February 2024 (UTC)