Stroboscopic Effect

Stroboscopic Effect is the visual phenomenon caused due to sampling of continuous motion in discrete steps. It can be observed in daily life, as the apparent change in direction of rotation of a fan when changing its speed. In some movies, the wheels of trains appear to go backwards (wagon-wheel effect), this is also explained by stroboscopic effect. Some videos of helicopters flying without any motion of the rotor are illusions that can be explained by stroboscopic effect: the shutter rate is a multiple of the revolving frequency of the rotor.




Predefined States

  1. The Stationary Rotor

    The perceived wheel appears near stationary to the observer. Notice the fact that the sampling rate is exactly twice of the number of revolutions per second. StandUpMaths' YouTube video


  2. Near-complete Aliasing

    The condition where the camera's shutter rate is so high that the discrete frames captured by it actually appear continuous to the eye.


  3. The Oscillating Rotor

    The perceived wheel appears to oscillate between three angular positions. This wass commonly seen in World War 2 fighter planes


  4. Wagon-wheel Effect

    The perceived direction of rotation is opposite to the actual direction of rotation. Professor Valvano's YouTube video


  5. The Sluggish Rotor

    The perceived wheel rotates in the same direction as the actual wheel, but with a slower perceived speed.



Note:
  1. Stroboscopic effect can also be introduced due to the limited frame rate of the screen and due to persistence of vision of the human eye.
  2. At speeds greater than 50 RPM, your eye perceives two spokes although only one spoke actually exists. This is due to stroboscopic effect caused due to the persistence of vision of the human eye.

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