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Old 7th November 2002, 12:18 AM   #1
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Default Can a magnetic field rotate axially?

If you get a loudspeaker magnet without any pole pieces attached and hold it up in free air, the magnetic flux comes out from one side and returns to the other side. Some goes around the outside and the rest goes through the center hole. Nothing controversial so far. Now, what happens if we rotate the magnet on its axis like a wheel? Does the magnetic field rotate with the magnet as some people say, or does it simply stay put? Modern theory has it that there is no such thing as “lines of force”, these are only an impression gained from putting iron filings on a sheet of paper and placing a magnet underneath. The iron filings do in fact group together in lines along the flux path but the flux itself is completely homogenous.

You would think that if the flux rotated with the magnet then you could place a wire near the magnet and measure an induced emf of sorts. The trouble is, when you do this you get an equal but opposite emf induced into the measuring leads of your meter as well that cancels out anything you might have measured! That is of course provided something *does* get induced. Either way, you measure nothing. People have been arguing about this since the days of Michael Faraday in the 1830’s. What do you think?

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Old 7th November 2002, 01:02 AM   #2
fcel is offline fcel  United States
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Speaking of forces, free air, rotation .... I'm curious ... is your avatar showing one of the flying pattern of a RC helicopter? Tunnel roll looping? If not, what does it symbolize?
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Old 7th November 2002, 01:23 AM   #3
SY is offline SY  United States
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A magnetic field is itself an abstraction. If you rotate a circularly symmetric magnet about its axis of symmetry, none of the physics changes. Whether or not you describe that as a "rotation" of the magnetic field is a matter of semantics, not physics.

If Helen Keller is walking alone in the forest and a tree falls, does it make a sound?
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Old 7th November 2002, 01:46 AM   #4
remp is offline remp  New Zealand
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What if you put a microphone near the tree and a very long cable out of hearing range would the mic pick up any sound.
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Old 7th November 2002, 09:41 AM   #5
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Default Not that deep-and-meaningful really.

Fcel, I ony found the arrow about a week or two ago. I first saw it about 1994 on the intro screen of a Super Nintendo game called Unirally, aka Uniracer. I was fascinated with the bounce in it's rotation. I just find it visually interesting, that's all. I may change it for something else one day, but for now it's what I like.
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Old 7th November 2002, 08:08 PM   #6
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A falling tree does not make a sound unless the resulting vibration intersects a nervous system in such a manner as to prompt said nervous system to comment,

“Hewh, Doggies. Did you hear that? Was that a tree falling? Man oh man, sounded like a bus hitting a water buffalo at speed.”

.... and/or something to that effect.

Vibration is not sound.

Sound is an aspect of perception.

Sound happens only in your head.
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Old 8th November 2002, 12:39 AM   #7
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Default Feel the heat, see the light, tune those airwaves.

Same with radiant heat and light. no different than radio waves, they just get interpreted by our bodies very differently.

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Old 12th November 2002, 07:22 PM   #8
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Man all this talk about perseption and such is pretty damn intersting.....Cosmic.....
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Old 14th November 2002, 03:01 AM   #9
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As I recall, relativity describes magnetism as the relativistic
distortion of an electrostatic field. If the magnet is rotating
there is an additional distortion, I imagine resulting in
a stronger magnetic field. However I think it's probably
easier to build a bigger amplifier and push the electrons
through the voice coil faster than it is to spin the magnet
at relativistic speeds.

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Old 14th November 2002, 03:09 AM   #10
halojoy is offline halojoy  Sweden
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that can be the problem with my audio output system
the electrons doesn't get enough speed
probably not enough speed for 20000 Hz
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