>
> At 08:19 PM 21/10/2003 +0200, you wrote:
> >What 'magnetic dipoles' ? You can use F=B*I*l (Laplace magnetic force)
> >where B/H=Mu for isotropic media (i.e. air coils and no armature).
> >H=I/(2*PI*d) at a distance d from an infinitely long wire carrying a
> >current I, and H=2*I/r in the center of a single turn coil of radius r,
> >H=N*I/l inside a long and narrow solenoid (the last formula is empirical
> >afaik - the exact version is very hairy). If the coil(s) have cores with
> >Mu different from air then B will be non-linear and probably change with
> >the inverse square of the distance if the distance between the poles is
> >reasonably large (larger than the diameter of the pole pieces) so
> >alignment errors do not play a major role. So F ~= N*I*B/(l*r*d^2) for d
> > >= 2r where B is the induction from a nearby magnet or other coil. Try a
> >book near you ?
>
> The very first thing I did was look in my old physics text book.  It didn't
> seem to be any help, which is why I came here.  Perhaps I should have tried
> a little harder to develop my own equation, I don't know.
>
> This all looks very helpful, but let me make sure I've got the variables
> right.  (sure would throw a wrench in the works if I had that wrong)
>
> F: Force
> N: number of turns in the coil
> i: current in the coil
> B: you stated
> L: length of the coil
> r: radius of the coil
> d: radius of separation between the coil and the other source of magnetic
> field.
>
> Now all I have to do is try to apply the Mu of a ferrous material (like a
> steel bolt) to this equation.
>
> Well, anyway, for a better idea of what I'm trying to accomplish, have a
> look at http://members.shaw.ca/annirak/index.htm, and have a look at the
> "[EE]: Active maglev with permanent magnets & solenoids" thread
>
> Thanks for the help, that's pretty well does it.

>It doesn't work, alas.
>It can be shown mathematically (Earnshaw, 1842) that it is impossible to
>produce STABLE static levitation using "normal" magnets.
>Many people have tried. Including me - even knowing about Earnshaw's
>theorem. I thought I may be able to "break the laws of Physics)(beam me up,
>Jim) by careful physical manipulation ("how could this arrangement possibly
>not work") but the properties of the magnets themselves get in on the act
>when you start arranging them in sheets. It takes more than that to break
>Maxwell's laws :-)
>
>It CAN be achieved using "a little bit more". Hence the Levitron top which
>adds spin, and various schemes using magnets plus diamagnetic materials such
>as Bismuth or graphite (or fingers) to add a negative non linearity to the
>field.
>
>Good basic introduction  at    http://www.physics.ucla.edu/marty/diamag/
>
>Using your fingers as diamagnetic material
>www.physics.ucla.edu/marty/diamag/magnet.pdf
>with a bonus piece on extra-ocular magnetic compass in newts ;-)
>
>         Russell McMahon

> So you want to let some futuristic models fly above a table?
> There's no way to do this with supercondutors or some kind of graphit!
> You have to think different.
> Use the repulsive forces of two equal magnet poles to let the model fly,
> and then use the attracting force of opposite magnet poles to hold
> the model in position! You'll have to use some more magnets for the
> fly than for holding.
> I think there's no other possibility to do this, unless you have  the money
> for an ultrasonics solution.
>
> MfG,
> Do.Pe.
>
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