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B Found something odd while procrastinating, fan/computer

  1. Jun 22, 2016 #1
    So while not doing what I should be I was cooling myself off with this tiny fan with a hand-crank. For some odd reason I decided to point it at my monitor and make it go in reverse and noticed that at a certain speed the blades of the fan appeared to be blue and yellow and rotating in the opposite direction of the actual rotation of the fan. What causes this to occur? I assume it has something to do with the refresh rate of my monitor but I'm clueless as to why this happens. Thanks in advance!
  2. jcsd
  3. Jun 22, 2016 #2
    It must be a stroboscopic effect, like in the movies when the wheels of the stage coach seem to be moving backwards.
  4. Jun 22, 2016 #3
    What about the colours? I understand that computer light is naturally heavily saturated with blue, however the polarising filter gets rid of most of that light, so where does the blue and yellow come from?
  5. Jun 22, 2016 #4
    The refresh rate must be different for the different colors.
  6. Jun 23, 2016 #5


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    It's a psycho-optic illusion. I don't recall its name so I can't find a reference to it. If I remember the demonstration, it includes a cylinder with alternating black and white stripes on its surface, parallel with the cylinder axis. The cylinder is spinning w/ axis vertical. I think there was also a strobe light involved. The illusion was that the black and white stripes were seen as colored stripes.

    I also seem to recall a similiar effect with a spinning disk with either radial or spiral lines on it to create color. I think there was a strobe involved here also.
  7. Jun 23, 2016 #6
    I think it's called the GBTWYB effect.

    Get Back To Work Ya Bum.
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