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  • The Wagon-Wheel Effect
    Posted by Elyse Moody 8:12 PM on Aug 31, 2010

    Props (pun intended) to my friend Drew, who just forwarded me an interesting video and the opportunity to learn something about optical illusions today.

    This video captures a bizarre effect: what appears to happen when you record an aircraft's propellers with your cell phone video camera.

    It's a good example of an optical illusion called the 'wagon-wheel effect' -- a new phenomenon to me. It happens when you record any regularly spoked wheel, including aircraft propellers (Drew tells me this looks like a Dash 8-Q400) and helicopter rotors.

    Movie cameras, including those on your cell phone, create stroboscopic conditions that break down the visibility of a rotating wheel into brief episodes where its motion is absent or interrupted by episodes of invisibility.

    The effect comes into use in aviation maintenance in certain tasks, such as adjusting the timing of an engine.

    This video illustrates the effect a little more clearly:

    Tags: om99, engines, illusions

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