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Magnetic repulsion force between two cylindrical magnets

  1. Nov 27, 2009 #1
    I'm doing an investigation where I am trying to find the repulsion force of cylindrical magnets. For this I have two ferromagnetic disk magnets on their sides, so that the curved sides face each other. In the investigation I push one of the magnets with a constant force towards a stationary one, and I'm trying to find the magnetic force between them the moment that the moving magnets has 0 velocity before it starts being repelled backwards. I then increase the magnetic field of the stationary magnet and repeat the process. I'm having trouble finding a way to determine this magnetic force. I have magnetic field sensors and can measure the distance between the magnets when v = 0.
  2. jcsd
  3. Nov 27, 2009 #2
    The stored energy is

    W = ½∫B·H dV = 1/2μ0∫B2 dV
    where dv is integral over all volume (includuing inside magnets).
    The force in the x direction is

    Fx = dW/dx

    Bob S
  4. Nov 29, 2009 #3
    I'm not entirely sure that this would work for me. I'm assuming that the 'V' is voltage, but I'm using permanent magnets and this seems like it applies to electromagnets?
  5. Nov 29, 2009 #4
    Voltage does not appear in this situation. The second magnet starts moving when the force exceeds the static friction force. It should be the same if the two magnets repel each other or attract each other. If you put the two magnets on a slope where gravity becomes important, you can measure the actual force by comparing the repulsion force to mg.

    Bob S
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