Apparent reversal by stroboscope

[vin300]

Why does a rotating object appear to freeze or reverse it's motion when viewed through a stroboscope?

 

[Drakkith]

This is called the stroboscopic effect: http://en.wikipedia.org/wiki/Stroboscopic_effect
It is similar to the wagon-wheel effect: http://en.wikipedia.org/wiki/Wagon-wheel_effect

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