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Discharge a magnetized bearing

  1. Jan 16, 2008 #1
    WE're usign a steel ball bearing for our physics rollercoaster project, and we happened to store the ball ontop of a decently strong magnet over the course of a few nights, and we believe that the ball is magnetized because the ball slows down at parts of our rollercoaster where there is any steel wiring that ties/supports the tubing.

    So basically we need to know how to discharge the ball, if it is at all possible that the ball HAS become magnetized. (We also removed some wires where the ball was stopping, and suddenly it could go much further, so that supports the theory) ... You tell us, can we discahrge it?
     
  2. jcsd
  3. Jan 16, 2008 #2

    berkeman

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    Staff: Mentor

    Best bet is to get another fresh ball bearing. (Better yet would be to swap it with the best team's ball bearing....., but that would be cheating.... forget I said that.)

    If that's not an option for some reason, you need to "degauss" the ball bearing. A degaussing field is an oscillating magnetic field that slowly decays over time, until it goes away to zero:

    http://en.wikipedia.org/wiki/Degauss

    If you move the ball around near a magnet, rolling it to all angles, and slowly move the ball away from the magnet, still rolling it all around, then you will be able to mostly degauss the ball. It may take some experimentation to get it right. You can test the results by seeing if the ball can pick up any iron filings or light pieces of metal like paper clips, etc.
     
  4. Jan 16, 2008 #3
    thanks! I will try my best to do that... Obviously since I don't haev amachine it won't be easy, and I can't determine whether it wil produce results but... Anything to get this thing rolling again.
     
  5. Jan 17, 2008 #4
    Ask around for an old-fashioned TV/radio repair shop. They probably have a deGaussing coil. If not, see if you can find a motor/generator/alternator repair shop; they should have sort of one though they probably call it a "growler". As a last resort, anyone who does bulk erasing of magnetic tapes should have one.

    The easy way to check the magnetism is to move the bearing over your computer monitor and see if it messes up the display.
     
  6. Jan 17, 2008 #5

    berkeman

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    No, no, no! Do not do that, or you may mess up the display (leaving residual magnetism in the shadow mask). Color monitors have built-in degaussing coils, but they are not generally sized strong enough to remove residual magnetism from having a magnet put up to the monitor screen.

    I made that mistake once, and that was enough. It took me a long time with a hand-held degaussing coil to get my TV back to normal. Ack!
     
  7. Jan 17, 2008 #6
    No guts, no glory. What's a little green in the corner of the screen gonna matter?
     
  8. Jan 17, 2008 #7
    Fixed that for ya
     
  9. Jan 18, 2008 #8
    Actually, I used to do this with a coworker's monitor until the day I really did magnetize the mask and had to get a coil to undo it before he found out. Now I just hold suspected magnets somewhere near and watch for tearing (I used to use my compass till I inadvertently switched poles).
     
  10. Jan 18, 2008 #9

    berkeman

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    Staff: Mentor

    :rofl:
     
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