Why do wheels seem to rotate backwards as they speed up?

Discussion in 'The Rumble Strip' started by Evolution., Mar 2, 2007.

  1. Evolution.

    Evolution. (Banned)

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  2. Jondot

    Jondot

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    Never seen it in real life. Ever. On TV it's the frame rate of the camera in comparison to the revolution speed of the wheel, or something, so maybe your eyes work in the same way. Our eyes can only see at 25fps (or 15, I forget), so maybe the same principle.
     
  3. Danoff

    Danoff Premium

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  4. wfooshee

    wfooshee Premium

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    TV or film is a series of stills, which real life isn't. If that series of stills shows the spoke advancing almost to the next spoke with each frame, your brain will see it as slightly reversed rather than well advanced.
    As the car accelerates, the effect will flip back and forth a couple of times.
     
  5. Barracuda

    Barracuda

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    i've always wondered this too. its fun watching a car speed up and the spokes seem to go backwards, then you can see them, then they start going backwards again.
     
  6. NoQuarter

    NoQuarter Premium

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  7. Wolfe

    Wolfe Premium

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    I can't remember if I've ever seen it in real life, but I've certainly seen it on TV and in games. Is it just me, or is Live for Speed particularly susceptible to the phenomenon, compared to other games?

     
  8. Puksis

    Puksis

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    When I drive my bike, and watch the front wheel and I slow down,
    It will "drive" backwards.
     
  9. Christhedude

    Christhedude

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    i've seen it pretty often on the highway...when i pass cars and look at their wheels, sometimes they seem to rotate backwards...
    :)
     
  10. Blake

    Blake Premium

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  11. wfooshee

    wfooshee Premium

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    Back in the days when music came on big black vinyl discs, we would correct the speed of our turntables by placing a calibrated printed sheet onto the platter and shining a flourescent light on it as it turned. The sheet had black squares on it spaced a particular distance apart. The 60-cycle strobe effect of the flourescent light would make the squares appear frozen if the turntable speed was exactly correct. A little slow, the squares appeared to creep backwards. A little fast, thay crept forwards.

    This strobing effect is the same thing described by the wheel spokes as they change speed. In video, the rate depends on frame rate. I've never seen it in real life in daylight, and barely at night, just a little bit under street lights. The sun is a non-strobing light source, while some street lights apparently exhibit the 60-cycle strobe.

    I'm thinking this is caused by road vibration being transmitted to your body, then your head, so your eyes are actually vibrating a bit. Just guessing.

    For more stroboscopic fun, put your hand in front of your TV or computer screen and wave it around. "Hello, monitor!" How many fingers does one hand really need?
     
  12. CDailey

    CDailey

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    Change the refresh rate on your monitor and try that again.
     
  13. LewyMan

    LewyMan

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    Now that is cool!
     
  14. GilesGuthrie

    GilesGuthrie Staff Emeritus

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    High-end and DJ decks have this built into the side of the platter. See the red light in the image below. Deck is a Technics SL1200.

    [​IMG]