[LMB] Quaddies' Toys

Ray RayLists at quixnet.net
Mon, 16 Aug 2004 19:05:43 -0400

James M. BRYANT, G4CLF wrote:

> Andrew Lambdin-Abraham replies to Dan Tilque:-
> >You might be able to simulate (gravity) given a sufficiently
> >sized/shaped magnet.  They both decrease in proportion to the
> >square of the distance, right?
> Sorry Andrew, wrong!
> [A] Gravity varies with the INVERSE square of the distance.
> (Nit-picking, I know, but important.)
> [B] Magnetic fields, in the absence of magnetic monopoles which
> may have been hypothesised but have not yet been discovered,
> are dipole fields and vary with the inverse CUBE of the distance.
> HOWEVER by using two magnets, or a solenoid, it is possible
> to produce a uniform magnetic field in a relatively small
> (but large enough) volume. And at the surface of a planet
> the gravitational field is also, for all practical purposes,
> uniform. (We're too far from the centre of mass for changes
> due to the inverse square law to be important over short
> radial distances.)
> James - pedant with a Physics (and Philosophy) degree

I have been trying to dig up what I learned in electromagnetic theory.  
I think I ended up curling my cross product; or maybe I got a low 
gradient in that class.  ;-)

Anyhow, is a uniform field going to cause the balls to move?  IIRC, you 
need a <ahem> gradient in order to get a net force on a ferromagnetic 

What kind of a field in that space would we need to provide in order to 
get a uniform attraction toward a given direction?