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Homework Help: Permanent magnets.

  1. Dec 17, 2006 #1


    I have a deeply magnetizing question. I have an attractive magnetic assembly and I am interested in finding some forces, acting on its parts.

    Set-up details ( if to be specific ):

    I have two cylinder-shaped neo magnets with identical dimensions and properties, such as residual induction, dimensions, mass, etc.

    I fix both of 'em as shown in the attachment A1.gif below. M1 is fixed on the ground, M2 can only move thru Y-axis. M2 is attracted by gravity, but hangs in the air because of the repulsive force between those two.

    I have to find the net force in Newton units, acting on M2, thus it's being fixed in its levitated state and doesn't move. The sticky point is that I want to design a magnet, which will hold another one at certain air gap, but for this purpose a horse, pardon, a force value needed.

    What I do know:
    I know nothin' about it, as the school project has just begun; this is my first week with permanent magnets. So my questions to you:

    • Could you provide me with any ( specific ) guidelines for further reading? Google did not help me a lot in this case.
    • or, could you give me some kind of hint for the strategy of calculation, which I should follow?
    • How the Magnetic Flux Density ( induction ) of a given magnet does relate to the resulting force?
    • I have gotten a link to so-called "magnetic moment" or torque as a force expression, but it just doesn't make sense, I am not sure it's what I need. Is it?

    I’m totally lost in this forest. Any help would be appreciated.. ..even if there are no threes.

    Lyric notes:
    When I’m talking about induction, I visualize the following calculation in my mind: see att. A2.gif
    The purpose of this project is to develop ( OK, to try to develop ) a magnetic ( frictionless ) bearing for the windmill. It is interesting to check – will it work or will it not do so.

    Attached Files:

    • A1.GIF
      File size:
      5.6 KB
    • A2.GIF
      File size:
      6.9 KB
  2. jcsd
  3. Dec 17, 2006 #2


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  4. Dec 17, 2006 #3
    All right, thank you for the help, I'll take a look at it. :redface:

    - - - - - - - - - - - - - - - -
    Now I understand..

    I've found most of the needed literature, and will make sure not to repeat this kind of mistakes in the future.
    Thank you for the right kick!

    Best regards,
    Last edited: Dec 17, 2006
  5. Dec 17, 2006 #4


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  6. Dec 18, 2006 #5
    Thank you, A. Zero.
    It is a very good information to start with. My current point of view is, that AMB's need an energy source, and therefore they are likely not to become useful in a windmill, because it is a bit risky and can cost a lot, if it fails.

    I'm trying to find out, what a PMB*[1] might be able to do. There is a tricky problem of fixed magnetic configuration, and some calculations have to be performed on this basis. So I am searching for the basic "rules" for the game, so to speak, because I am startin' from the beginning.

    What our group wants to do - is to allow a windmill to start at lower wind speeds due to reduced energy loss by using a frictionless PMB assembly, and if we can't build it, we will model it. Inspiration came from energybulletin.net, or more precise, from http://www.worldwatch.org/node/4217" [Broken] - the difference is, that we want to build and test our own.

    Best regards,

    *[1] Passive Magnetic Bearing.
    Last edited by a moderator: May 2, 2017
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