Magnets

[gerkin]

Do magnets (non electric) lose power the more they are used.  For example if one is repeatedly lifting an object by levitating it from a table up to the magnet the Potential and Kinetic energy must be coming from somewhere. ?

[Space]

if you're holding the magnet with your hand,
then the energy comes from your arm.

[Clanad]

Interesting theory, Space..

However,   the material in a magnet is inherently magnetic and that will not go away as long as it is not heated. However, not all portions of the magnet must have the same magnetic field direction.  These magents are divided into "domains".  To get the material to behave as a magnet, one domain must be increased in size, so that it
dominates.  An "unmagnetized" piece of material just has equally sized domains with fields pointing every which way.  To magnetize an object like this, you put it into a large magnetic field and wait (to speed things up, hit it with a hammer or warm it up some).  To demagnetize it, put it in a weak field (the earth's) or a differenly directed field and wait.  If heated to a temperature termed the Curie Temperature, magnetic materials will lose their magnetism... Additionally, with a strong enough magnetic field of opposite polarity, it is possible to demagnetize the magnet.  Finally, simple iron bar magnets, such as children's toys, can lose their magntism  via a shock, such as being dropped or hit with a hammer. (Partial Source: Physics and Astronomy On Line)

[Hamish]

An interesting patronising comment Clanad.

In fact it is not the size of the domains that is important but their orentation. Heating/shock allows the domains to randomise causeing loss of magnetic properties. The domains can be realigned by applying a strong mag feild.

With regard to the question space is correct. The force comes from the magnet, but it is applied to both the arm and the object. if the arm remains in position then the force on the arm, as the object is raised will be the same as picking up the object with the hand (ideally) therefore the same amount of energy is expended by your arm.

[Space]

What I meant is:

If you place a magnet above an object and the magnet lifts it,
then you have to spend energy separating the object and the magnet.

So whatever energy the magnet gives, it takes back.

It's a bit like gravity... dropping an object can provide energy but then you have to lift it back up again! so you don't gain any energy in the end.

[Hamish]

I understand what you are saying space, however there is no net gain or loss of energy from the magenet otherwise it would get hot/cool during the process.

[gerkin]

Space, so you are suggesting that the magnet is getting �recharged� by the process of separating the object, i.e. acting a bit like a generator (the object displacing the magnetic field causing a flow of energy back into the magnet).

[Clanad]

Interesting comment, Hamish... You seem to be able to read intent into three words...

[Space]

Hamish,
why would the energy have to be converted to heat?
Thinking about it, I don't think energy is actually stored in the magnet...
I suppose it is just potential energy available to the system "magnet + object".

When the magnet and the object are far away, there is a potential energy available. This energy is converted to kinetic energy when they get closer. When they are as close as they can be, there is no potential energy left.
By separating the objects (using energy from your muscles), you give this energy back to the system.

So yes, the system is rechared by separating the objects.

[Hamish]

To clarify, it was the term 'energy the magnet gives' which is confusing. The magnet does not give any energy to the system, the arm etc that move it does. Things which do work - ie expend energy - do so inefficienty an therefore radiate energy ususally as heat. therefore if there was any energy exchage with the magent you would expect it to get hot.