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Why do car wheels spin backwards

  1. Jun 4, 2009 #1


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    Anyone who's looked at a spinning car wheel or fan notices that sometimes it looks as if the wheel/fan is spinning backwards. I was once told that this is because of the fact that the light shining on it, coming from an electric light source, turns on and off at a certain frequency (~50Hz) and therefore we get a stroboscopic effect.
    But I see this effect even in daylight - which is constant. What could be the reason for this? Could it have to do with the rate that our eyes can "refresh" the picture sent to the brain?
  2. jcsd
  3. Jun 4, 2009 #2


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    I think it has something to with the time taken for one fan blade to reach the position of the other one, being less than the time take taken for the light to reach your eyes. Granted I never really followed up on that explanation, but that was what I was told when I was young.
  4. Jun 4, 2009 #3


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