From: charlie@elektro.cmhnet.org (Charlie Smith)
Subject: Re: Courier bag:  Do you have one?
Summary: pfizzicks attack!
Organization: Why do you suspect that?
Distribution: na
Date: Tue, 26 Jan 93 23:12:12 GMT

In article <1993Jan25.160940.12158@rd.hydro.on.ca> jlevine@rd.hydro.on.ca (Jody Levine) writes:
>In article <1993Jan22.212815.461@pages.com> bigdog!jon (Jon Wright) writes:
>>
>>I asked somebody at MotoPort about this and they said the ceramic magnets,  
>>which were more powerful than the previous metalic ones, were also polarized or  
>>uni-directional or something, which prevented screwing up your disks and cards.   
>All together now, "There's no such thing as a magnetic monopole!" No? That
>wasn't what they meant? What did they mean, then?
>
>Take two fridge magnets, you know, the rubbery kind, and try to stick them 
>together. They will hold together, but only if they're offset by so many
>milimetres. If you try to move slide them against each other, they won't
>let you, or they will but will resettle somewhere else, but not in between.
>These magnets are made so that they alternate (north-south)-(south-north)-etc.
>along their surface, so the dipole is not one surface north and the flip side
>south, (magnet a) but a bunch of dipoles laid flat along the surface (magnet
>b). 
>
>Now imagine the magnetic field of magnet a, with one side north 
>and the flip side south. Draw two poles on a piece of paper and draw lines
>through the magnet from north to south. Turn each of the lines into a closed
>path by drawing lines around the outside of the magnet putting arrows on
>the lines to show which way you went. See? Outside the magnet, no matter 
>how far away you are, there are lines going through you and you're sitting 
>in a magnetic field. It get's weaker as you go away, but it's still there. 
>Now, on the same piece of paper, draw another dipole, in line with the 
>first, but pointing the other way (you now have four poles in a row). Draw 
>the associated field lines. If you're close to either of the dipoles, you 
>feel the effect of that one. If you're far away, the fields cancel out and 
>you feel nothing. Ok, so you have to be a lot closer to a string of opposing, 
>end to end dipoles to be in the field. Likely, all the manufacturers have to
>do is put a layer of foam between the magnet and the bag interior, or laminate 
>some non-magnetic plastic to the inside of the magnet and you're out of the 
>danger zone. If they're doing anything fancier, I'd be interested to know.
>
>When it's sitting on your tank, things get even better for your sensitinve
>tankbag contents. Field lines are picky, and would much rather be in a 
>nice, ferromagnetic metal than in air, bits of plastic, or dirty socks.
>If you drew your dipole with half the lines on each side, lay the dipole
>down on your gas tank and some of the lines will move to the tank side,
>leaving less field in the bag. This is why your bag sticks to the tank, as
>having the magnetic flux return through steel is a lower potential-energy
>state than having it return through air.

Awright !!     But, all you have to do is take the bag off the tank, and
those Magnetic Lines of Force (MLoF) are no longer "less in the bag" while
taking the easy path through the tank ... the MLoF will jump back into their
original symetrical pattern, meaning - through the tank bag.

Disruption of the magnetically oriented particles in a diskette (etc) only
really occurs during periods of change of the magnetic flux - a steady state
flux field won't normally change things, but the changing flux while putting
the bag onto the tank or removing the bag from the tank is more likely to
cause things to get fluxed up!   *Bzzzzt*    Sorry, couldn't help myself.

 
>I've        bike                      like       | Jody Levine  DoD #275 kV
>     got a       you can        if you      -PF  | Jody.P.Levine@hydro.on.ca
>                         ride it                 | Toronto, Ontario, Canada


Charlie Smith   charlie@elektro.cmhnet.org  csmith@dsac.dla.mil  whois ces10
  DoD #0709   doh #0000000004  &  AMA, MOA, RA, Buckey Beemers, BK Ohio V
                BMW K1100-LT, R80-GS/PD, R27, Triumph TR6
                          Columbus, Ohio USA