stroboscopic eyes

[kowalskil@alpha.montclair.edu]

Ke Fox  kfox@shhs1.smoky.org  wrote:
> .... seeing wagon wheels in movies seeming to roll backwards. Students 
> maintain that they have seen this in cars with naked eye. I don't inderstand 
> the mechanism of how that would happen, yet in retrospect, I think I have 
> seen it, too. Any ideas?

Seeing this with the naked eye * in a movie * is not surprising. Suppose 
the movie has 25 frames per second and a wheel makes exactly one or two 
spokes during 1/25 sec. In that case the wheel will appear as not turning. At 
a slightly slower speed the wheel will appear to turn backwadrs. In this case
the camera acts as a strobe. I do not believe that a naked eye without a
device of some kind can produce the stroboscopic effect. Ludwik.