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If you watch this Amazing Water & Sound Experiment #2 YouTube video, you can see an amazing effect with water, a sinusoidal signal and a woofer.

Is this a true effect due to vibration of the pipe generated by the sine wave? Is it just a hoax?

  • Seems legit... need to dust my Arduino... Related: youtube.com/watch?v=mODqQvlrgIQ#! – nico Mar 24 '13 at 13:45
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    A key part to understanding this video is that the video camera is taking 24 frames-per-second. In real life, looking at it with your eye, it would look quite different. For example, if you put your finger between the apparent crests of the wave, where it appears there is no water, your finger would get wet. The water isn't following a path that bends 90 degrees every few cms. – Oddthinking Mar 24 '13 at 13:51
  • + @Oddthinking is right. If you've ever waved a garden hose, and watched stroboscopically lighted water streams, you can see it's no mystery. Upvoted because it's such a cute demo. Thanks. – Mike Dunlavey Mar 24 '13 at 15:53
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    This was answered in Physics.SE 11 days ago. – RedGrittyBrick Mar 24 '13 at 16:06
  • As others have explained, the video is real, and the effect is caused by having the speaker in sync with the video frame rate. For a full explanation of the video, have a look at the Bad Astronomy website – hdhondt Mar 25 '13 at 0:42
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Yes, what you see is real. However, as @Oddthinking points out, this happens because of the sync between the frequency of the camera and the frequency of the sound wave. If you make this experiment at your home without a camera that is shooting at the same frames per second (fps) rate as the frequency of the sound wave you'll not see the same effect with your naked eye.

The drops don't flow in a sinus form. There is a drop of water at the same place every 1/24 second due to the frequency of the wave sound. Each drop goes in a straight line, but the stream of water returns to the same position every 1/24. When looking at this at a frequency of 24 frames per sec, you see as if there is a stream that is "suspended" in air in a shape corresponding to the wave. If the water source is allowed to move then you get a "sinus wave", if you hold the water hose and change the flow strength at 24 Hz, you will see droplets "suspended" in air, as shown in some of the videos below.

The same phenomena can be seen on the following videos as well:

The phenomena was explained by @RedGrittyBrick on Physics.SE:

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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    I think the answer “yes” is misleading or wrong. It does not form a zig-zag flow. It emits droplets whose relative position creates a zig-zag figure, but they don’t form a zig-zag flow – the flow direction of each individual droplet is a normal parabole. – Konrad Rudolph Mar 24 '13 at 21:09
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    @Konrad: Agreed, but the OP set up a bit of a false dichotomy. Yes it is real, in that it is not a hoax. – Oddthinking Mar 24 '13 at 21:21

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