Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 13/08/2012 16:30:02

Title: How does a magnet apply a force to a body?
Post by: thedoc on 13/08/2012 16:30:02

Shaktyai asked the Naked Scientists:
   
When a permanent magnet lifts up a weight (a steel ball for instance), which force is working (magnetic force does not produce any force)?

Griffith addresses the problem for an elctromagnet and shows the generator is providing the energy.

So if one can exclude the energy stored in the field for an electromagnet, there is little chance it is the dominant term for a permanet magnet.

My guess is domain reconfiguration.

Any idea and link to a paper/book welcome.

What do you think?

Title: Re: How does a magnet apply a force to a body?
Post by: Soul Surfer on 13/08/2012 21:28:13

In a permanent magnet the unpaired electrons link together locally as you say to produce magnetic domains.  These domains are then realigned by the magnetic field that creates the permanent magnet which in the presence of zero field stays realigned.

Let us assume that the ferromagnetic object the permanent magnet lifts up has no net magnetisation As it approaches the permanent magnet  the field of the magnet induces opposing magnetism in the object that is being picked up this secondary field creates the magnetic attraction and also stressed the field of the permanent magnet but cannot destroy it because it requires more energy to do this than the field that the magnet generates.  there is a net sharing of energy because the energy lost in the stressed field of the permanent magnet equals the energy input into the unmagnetised object to create the field.  agreed it is quite a difficult concept when you go into it fully.