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A video posted on Youtube.

How does this phenomenon work? I know he is using frequency to propagate water in a sine/cosine wave, but how does it exactly work this way? Why do we see it as if its paused, or in slow motion, or even in reverse?

Can someone please explain this? I am intrigued by the video and want to know it's physics.

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I also am intrigued. I think human vision operates at 8 htz. That is why we can't see fluorescent light tubes (which operate at 50htz) blinking: because 8 and 50 rarely coinicide in sequence. Perhaps there is something in the fact that 8 and 24 do conicide frequently (no pun intended) that results in an harmonic resonance which we see manifest as a sine wave. Further than that I cannot speculate at this juncture. –  user22609 Mar 31 '13 at 10:57
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2 Answers

up vote 11 down vote accepted

It's a visual illusion akin to the Wagon Wheel effect

The stream of water is being waggled back and forth by a 25 Hz audio signal and being filmed at 25 frames per second.

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So only because the camera cannot capture at higher frequencies, it picks up this effect ?? Howcome the Wagon Wheel effect works on our eyes ?? If you look at a vehicle's wheels, the effect appears, howcome ? –  Fendi Mar 13 '13 at 22:45
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The wagon wheel effect, with bare eyes, works at much higher frequencies, precipitated by noise. You can change the apparent motion by humming! Do read the wikipedia link. –  Emilio Pisanty Mar 14 '13 at 1:15
    
You could also see this with a stroboscope, though that is arguably cheating. –  Emilio Pisanty Mar 14 '13 at 1:16
    
Will do, thanks. –  Fendi Mar 14 '13 at 1:23
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If you were standing in front of it looking at it, you'd see nothing special. The effect comes from the fact that camera's capture images at a rate considerably slower than the eye does.

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Thank you for clearing that up, more info would have been better. –  Fendi Mar 13 '13 at 22:46
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protected by Qmechanic Mar 31 '13 at 11:05

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