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Old 28th July 2003, 07:13 PM   #1
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Default Bizarre Phemomenon ?

Today I was making a floating rack ala Relaxa from SAP. My scalemodel is build from to pieces of MDF with magnet in between them with equal polarities to eachothor so they reppel. I also had some aluminum tubing.

When I let a magnet (12mm diameter) fall down this tube (16mm) it falls really slow !!!!
When I attach some iron object to the magnet and let it fall it doesn't even touch the sides !!

Can anyone explane this (aluminum being diamagnetic). It doesn,t matter how big the magnet is or what shape It just falls really slow inside aluminum ???

Ralph
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Old 28th July 2003, 07:35 PM   #2
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Default ruff explanation

A similar effect is had with copper.

A current is induced as the magnetic field passes the metallic object. A proportionality opposite force is induced as the field from the current reacts with the magnet.

Many educational physics labs will have a big copper disk and big old radar magnet to demonstrate this. Drop the copper between the poles and it falls very slowly. Hold the copper and move it in any direction and you can feel the opposing force.

Iím sure someone here can give a much better explanation...

Meanwhile here is a nice link explaining Eddy currents...

http://www.exploratorium.edu/snacks/eddy_currents.html

Who are Eddy currents named after?

Its a good and fun question. Perhaps the Mods will want to place it in "Everything Else" so more people will see it.
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Old 28th July 2003, 10:48 PM   #3
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Old 29th July 2003, 09:41 PM   #4
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Default DIY Eddy currents or Diekermann currents

Most of us of course are aware of the famous DIY Audio sparing matches that take place when Fred and Steve get together.

Perhaps we should refer to it as the Eddy-Diekermann effect.

Overshooting, ringing and blowing up mosfets if you build stuff based on irresponsible advice

(Likely not the first or last to make the obvious Steve Eddy current pun)
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Old 29th July 2003, 10:18 PM   #5
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Default the Eddy-Diekermann effect

Is a rather large area effect that is normally measured in mili-Eddy-Diekermanns or micro-Eddy-Diekermanns, to make it manageble.
Although large in area, the total energy is small, and since energy = information, at the end of it all, once the measurements have been made, we're none the wiser.

BTW Who said they had some current puns?
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Old 29th July 2003, 10:54 PM   #6
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Default EDDY-DIECKMANN EFFECTS...

Hi,

Quote:
Although large in area, the total energy is small, and since energy = information, at the end of it all, once the measurements have been made, we're none the wiser.
ROTFLMAO...

Nomenclature:

MOS-FET.

My Own Simple- Field Effect Transformer.

AKA:

MOst Serious-Formidable Ego Tripper?

Oops,
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Old 29th July 2003, 11:09 PM   #7
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Default Re: the Eddy-Diekermann effect

Quote:
Originally posted by dhaen
...once the measurements have been made, we're none the wiser.
Objectively, you are totally correct, however in my subjective tests, I find although the increase in micro detailing is initially illuminating, the overall long term experience is very fatiguing...
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Old 30th July 2003, 12:23 PM   #8
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Ask SE about Self Induction.

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Old 30th July 2003, 12:48 PM   #9
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Default Re: Bizarre Phemomenon ?

Quote:
Originally posted by rwagter

Can anyone explane this (aluminum being diamagnetic). It doesn,t matter how big the magnet is or what shape It just falls really slow inside aluminum ???
Eddy currents being generated in the aluminum see the resistance of the aluminum, causing a counter emf, thus counter magnetic field, slowing the fall of the magnet. I believe the only requirements of the tube is that it is conductive.

I've used this trick to entertain many children and friends. However I cannot take credit for finguring it out. A friend of mine at Fermi National Labratory showed it to me!


For similar effects look into magneto-forming metals:
http://www.teslamania.com/
(look for the shrunken coins link, and theory link)

-Dan
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Old 30th July 2003, 01:02 PM   #10
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This principle is widely used for braking purposes:

http://www.telmausa.com/telma_htm/default.htm

Another funny application was the checking of coins in public phones. After a coin had passed the checks for diameter, thickness and weight it was dropped through a gap with a magnetic field in it (i.e. this time the magnet is fixed and the conductor moving). The passing time (which is dependant on the alloy) was then measured optoelectronically.


Regards

Charles
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