Assuming that when a permanent magnet is attracting or repulsing to
another magnet it is doing WORK.  Will the magnetic energy in the
permanent magnet deteriorate faster than a stand alone magnet? If so,
which will be deteriorate faster? attracting to another magnet? or
repulsing to another magnet?
(All magnets have the same volume and grade)

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Request for Question Clarification by alienintelligence-ga on 14 Sep 2002 03:18 PDT

Hi martian...

Alien here ;)

What are you defining as a "stand alone magnet"?

Can you tell us the materials of the magnets that
you have in mind for this question? Different types
will react differently when attempting to modify
the magnetic fields. Will both magnets be of the 
same type (is that what you meant by grade?)


thanks
-AI

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Clarification of Question by martian-ga on 14 Sep 2002 04:54 PDT

Magnet material: typical (all the same kind)

Magnet shape: a regtangular block (again, all the same)

Grading: different grade has differnt power; just assume they a all
exactly same kind of magnet with same characteristics.

Stand-alone magnet: neither attracting nor repulsing to any object or
magnet.

Hi Martian
		Your question can indeed be answered for general situation,
 without considering specific materials or shapes.

There are two physical quantities involved here: Energy and dipole moment.

They are related, as shown on picture in this URL
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magpot.html

Magnetic moment measures the strength of the magnet.

The (magnetic potential) energy is not  property of the magnet but of the
configuration of the system ( which may consist of the magnet, other magnets,
pieces of iron ...).

So, in the simplest terms: you move the objects around,
the permanent dipoles are unchanged (hence the name)
 induced moment change
and
energy of the system is changing as you do or use work.


In the second aproximation, a horse-shoe magnet which is 'shorted' by piece 
 of soft iron will deteriorate more slowly.  This is not related to
energy change (of bringing the iron to the magnet) but becouse the
'strain' is less - and so internal relaxation is more slow.

Does this makes sense?

Please do rate this or or ask for explanation

hedgie

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Request for Answer Clarification by martian-ga on 16 Sep 2002 18:10 PDT

My understanding is that if...

2 magnets attracted together, their magnetic potential energy will
deteriorate more slowly than when 2 magnets put together repulsively.

Clarification:

"Deteriorate more slowly" - that's mean relatively I suppose?

In terms of time, if the energy of the 2 attracting magnets will begin
deteriorate after 100 hours, then relatively when will the 2 repulsing
magnet deteriorate?

Or will this be a concern since permanent magnet will generally keep
it's magnetic potential energy for a very long time. (without exposing
to extreme hi/low temperature)

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Clarification of Answer by hedgie-ga on 17 Sep 2002 21:40 PDT

Hi Martian

             Let's first clarify our terminology - so we are 
calling the same things by the same name.

The first question is: Do permanent magnets loose their power?
Answer is YES. It takes a long time at normal condition and is faster
under certain condition, such as high temperature, as described here:
http://www.physlink.com/Education/AskExperts/ae472.cfm

Such loss of magnetic power, is called deterioration. Magnetic moment
decreases with time. Under normal condition, for a good magnet, that can
take years. The ability of magnet to retain it's strength is measured
by coercitivity - a property of material.

The second term is potential energy: Imagine two permanent magnets: 
One is fixed, the other you hold in your hand, like shown here:
http://my.execpc.com/~rhoadley/field06.htm

You keep this orientation ( N to S and S to N) so that they attract.
To pull them apart you have to supply work -- energy of the system is 
INCREASING. You let them come closer, your hand goes with the pull and the
ENERGY of that system is DECREASING.  Usually, we do not say 
'energy is deteriorating' in this context to avoid confusion first phenomenon.

So, if we adopt this usual terminology:  Two bar magnets attracting (as above)
and to bar magnet repulsing (S to S and N to N) when held fixed, will keep
their magnetism for long and about the same time. It will not be concern in
any normal experiment or application (lasting days or weeks).

Over very long times (decades), or at higher temperature, the both will
loose someo f their magnetism (dipole moment) and as a result of that the
magnetic energy stored will decrease a bit. 
For repulsing orientation the rate of this decrease will be a tiny bit higher.

Does this answers yiur question?

Search terms: magnetic field, bar magnets, dipole moment, deterioration,
coercitivity.

Search is complicated by many many pseudoscientific posts on the topic
of animal magnetism, pertual motion machines and healing powers of magnets. 
So, be selective. A good textbook, for example Hewitt: Conceptual Physics
may be more useful then internet in this case.

Good luck

hedgie

Working magnets used in permanent magnet lifting machines typically
last about 25 years.  Each lift causes deterioration due to the work
done by the magnet assembly.  The magnets are replaced in these large
lifters at that time.  In permanent magnet motors, the loss of
magnetism due to work is not noticed because the mechanical parts of
the motor fail long before any significant deterioration of the
magnets.

Stored energy in a magnet can be calculated by measuring the
circulating current and using, as example, 25 years time (life
expectancy) for this magnetic current to flow.  United States made
high grade neodymium magnets store the approximately 7500 watts per
pound for their useful life.  The stored energy can be found taking
7500 watts times 25 years equal to about 1.6 million kilowatt hours
per pound.

To your question, assuming coercive force is not exceeded or the
magnets are not discharged by other means, you can calculate the work
done in attraction or repulsion by standard work formulas using path,
distance, and force required.  This work can then be compare to the
stored energy of the magnet and a value for the life expectancy of the
magnet system can be calculated.  The exact value is dependent on the
constants of the magnetic material choosen.