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Perpetua mobile theoretical misunderstanding

  1. Aug 10, 2013 #1

    I was patent examiner on the Portuguese patent office for 3 years and we have a lot of perpetua mobile applications, so I wanted to find now, the theoretical misunderstanding I'm missing here


    Imagine you have a track (on a table, on the xOy plane) on which a metal ball would follow, and at a certain length of the track, there would be a tubular permanent magnet, that would create a force on the ball accelerating it. That ball would be accelerated every time it passes through the tube!

    I know that there is some paradox on my lemma, but I can't find where

    Thank you in advance

    PS: Actually I know that the magnetic field is conservative, but something is missing

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  2. jcsd
  3. Aug 10, 2013 #2


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    Staff: Mentor

    The tube will not accelerate the ball around the track. I'm not sure what will happen inside the tube since the flux is so uniform, but once the ball leaves the tube it will be attracted right back to it.
  4. Aug 10, 2013 #3
    That's what I can't understand because every time I see images of magnetic field I see this


    By the way, I know that the force is [tex]F=q(E + v\times B)[/tex]

    But how to relate the Force created by the magnetic field of a permenant magnet if the ball is stopped, v=0, and there is no Electric field

    You said the ball would came back, but can't we shield the field, so the field just applies inside the tube.

    Sorry, too many questions
    Last edited: Aug 10, 2013
  5. Aug 10, 2013 #4

    Vanadium 50

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    Sorry, but we do not discuss perpetual motion machines on PF.
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