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# Re: [femm] Re: Incorrect force direction

- To: <femm@egroups.com>
- Subject: Re: [femm] Re: Incorrect force direction
- From: "Greg Watson" <gowatson@asiaonline.net.au>
- Date: Thu, 4 Jan 2001 16:13:34 +1030
- References: <NHEBIHNJBDNGFALCCCCIKECPCAAA.tickle@aem.umn.edu>

    ----- Original Message -----
    From: "Rob Tickle" <tickle@aem.umn.edu>
    To: <femm@egroups.com>
    Sent: Thursday, January 04, 2001 3:21 PM
    Subject: [femm] Re: Incorrect force direction

    > I tend to trust this result, but I would be interested in seeing some pics
    > of Greg's actual setup and magnets. I know the NdFeB magnets are highly
    > anisotropic and very strong; one possible source of stray force to look out
    > for would be if the magnetization direction of the magnet were not
    > completely perpendicular to the bar surfaces. Does the actual setup show a
    > true centring force in the center of the bar; i.e. does the force direction
    > switch signs as you roll past the middle?
    >
    Hi Rob,

    I'll see what I can do over the weekend.

    One of the basics of my "seat of the pants" approach to estimating ferromagnetic
    force direction is that a MMF source will be drawn toward a area of lower
    magnetic reluctance.

    The area of the rails and volume of the air to the right of the magnet should
    show lower magnetic reluctance than that to the left of the magnet due to the
    larger amount of inward facing rail surface and larger air volume between the
    parallel rails and thus the magnet should be drawn into a equal & balanced
    magnetic reluctance neutral point in the horizontal centre of the parallel bars.

    It's not rocket science, just common sense ferromagnetic stuff.

    Greg.

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    - From: "Rob Tickle" <tickle@aem.umn.edu>

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