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Calculation of magnetic force on a wire

  1. Nov 21, 2012 #1

    I would like to know if it is possible to move a steel wire against frictional forces using a magnet. What would be the approach of calculating the force acting on that thin wire. I would know the dimensions of the wire and the dimensions of the magnet. What other values should I find from data table.


  2. jcsd
  3. Nov 22, 2012 #2

    Simon Bridge

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    It is - you can easily see this with any handy magnet and a bit of wire since all normal situations involve friction to some extent.
    Same as any force calculation - or you could measure it directly.
    Which forces do you need to calculate?
    Take a look at the equations and definitions of the forces and see.
  4. Nov 22, 2012 #3
    You can definitely attract steel with a magnet, but the force is seriously complicated to compute. Don't hope for anything like B*I*L. It depends on how the wire's permeability deforms the field.
  5. Nov 22, 2012 #4

    Simon Bridge

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    ... but it is the sort of thing sometimes offered as a homework problem in college e-mag courses. The geometry is usually simple and permeabilities are provided. I agree it's usually a pain. We really need the context to be of real help.
  6. Nov 26, 2012 #5
    What I am really trying to do is move a length of wire along a duct, from outside the duct. I will be doing it experimentally. However, it would help if I could calculate the strength of the magnet I would need rather than trying to guess and do it by trial and error.
  7. Nov 26, 2012 #6

    Simon Bridge

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    Start with an idea of the range of choice for magnetic strengths that will be available to you. If they only supply the one magnet, there's no point :)

    Anyway - that will tell you how coarse-grained you need the calculation.

    I take it the wire is expected to be lying lengthwise in the pipe?
    How thick is the pipe and what is it made of?
    How big and heavy is the wire?

    Also see:
    http://www.corrosionist.com/magnetic_response_stainless_steel.htm [Broken]
    ... I'm guessing the wire is not stainless steel, but the discussion will give you an idea of what you are asking. eg. different kinds of steel respond differently to a magnet.

    I'd expect a basic classroom bar magnet to be able to move a gram or so of steel wire through a few mm of PVC plastic though. I'd just use the biggest magnet I can easily carry.
    Last edited by a moderator: May 6, 2017
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