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slow-rotor illusion


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I was watching this video from a link off of vertical magazine's website,




and had to ask why the main rotor looks like its making what looks to me about 50rpm. I've seen the same thing on cars and such, but never had it explained. Any physics majors care to share?


On a different note, I think I'll also continue to pay my taxes so if I ever dump a kayak like the dude in the video, I can have 9 aid cars and helo rescue my wet butt.

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Video is shot in frames per second. A video is really a collection of still photographs that are shown fast enough it gives the impression of fluid motion.


Imagine that your video camera recorded video at 24 frames per second. Now imagine that a wheel made 24 revolutions per second. Because the wheel would make one full revolution every time a frame is captured by the camera, the wheel would actually appear to not be moving at all. If the wheel made 23 revolutions per second it would stop just short of a full revolution at each frame capture giving the appearance of rotating backwards.


What you refer to is an illusion created by the difference between the frames captured per second by the camera and the RPM of the spinning body being recorded.

Edited by Fiasco
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