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A comment on Cow Magnets. Parent comment

Re:Cow Magnets by planede on Wednesday April 10, 2024 @05:05AM (#39988543)
It's 1/r^4 for magnetic dipoles, where both have fixed a fixed dipole moment. So it's 1/r^4 between two permanent magnets.

Where one object is a permanent magnet and the other is some unmagnetized ferromagnetic/paramagnetic piece metal, then the dipole moment of that piece of metal also depends on the distance. Assuming it's proportional to the magnetic field of the other dipole (~1/r^3) then the force is going to be ~1/r^7 for this pair of objects.

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Re:Cow Magnets by marcosdumay on Wednesday April 10, 2024 @10:46AM (#39991285)
Oh, that's right.

But magnetization is famously path-dependent, so now I'm tending to believe the force will be closer to 1/r^7 when moving on the direction of the magnet, but 1/r^4 when moving away. And not exactly any of those functions.

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Re:Cow Magnets by planede on Wednesday April 10, 2024 @11:51AM (#39992093)
Do you mean that the ferromagnetic material gets magnetized and retains some magnetization while moving away?
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Re:Cow Magnets by marcosdumay on Wednesday April 10, 2024 @01:58PM (#39993785)
Yes.
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