This is What Happens When You Run Water Through a 24hz Sine Wave

http://www.thisiscolossal.com/2013/03/this-is-what-happens-when-you-run-water-through-a-24hz-sine-wave/

by alexholehouse • 13 years ago

95 38 13 years ago

jared314• 13 years ago

Petapixel[0] has a better explanation. It is an illusion created by the synchronized frame rate and oscillation. They have used the same trick with a strobe light for live effects.

[0] http://www.petapixel.com/2012/04/24/sound-and-frame-rates-us...

DanBC• 13 years ago

YouTube has a bunch of videos showing strobe light version. Here are two short videos - the second one shows the effect nicely.

(http://www.youtube.com/watch?v=OtxlQTmx1LE)

(http://www.youtube.com/watch?v=ZRlNOyxWWf8)

alexholehouse• 13 years ago

I feel like there's some information theoretic approach which could be leveraged here, and maybe in similar systems - ie. just from the video we can work out

- The difference in video frame rate vs sound frequency based on the period of the wave

- Maybe the structure of the wave itself based on the waveform, although maybe not.

darkarmani• 13 years ago

Nyquist-Shannon: http://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_samplin...

mvanveen• 13 years ago

Wait, if I'm interpreting the Shannon-Nyquist theorem properly here, doesn't that mean since the signal is 24 Hz that we'd want a 48 FPS frame rate to accurately get the signal?

noonespecial2• 13 years ago

"This is What Happens When You Run Water Through a 24hz Sine Wave"

I'm not sure this is the best title. "What happens when you wiggle a hose at a frequency close to a camera's frame rate and then film the water coming out of it" might be better.

At the most basic level, this is just the game you used to play with a hose when you were a kid by waving the end and producing ribbons of water in the air. The video just added a camera trick to photograph the ribbon in the same place during each oscillation appearing to freeze it in place.

Initially I thought this was going to be much cooler, actually using the speaker to move the air through which the water was travelling to produce an effect. I was hoping for an awesome standing wave demo or something.

JDGM• 13 years ago

"The video just added a camera trick to photograph the ribbon in the same place during each oscillation appearing to freeze it in place."

This is such a concise summary and I'm totally with you. I think. If I understand right, it would not be impressive to watch in real life and is just a property of the recording. Correct?

catshirt2• 13 years ago

unless you internally processed images at 24 frames per second, yes.

however you'd be hard pressed to simulate this manually without any wave generator, which is why the speaker is crucial to the illusion.

mistercow2• 13 years ago

This is correct, although if you saw it in person lit by a strobe light flashing at 24 Hz, you'd see the same effect.

ars• 13 years ago

It's important to remember the water does NOT actually move in a wiggle like that.

Obviously it's impossible for water to change directions like that without something pushing it.

Instead the end of the hose is shaking, causing some water to flow on the left of the screen, and some on the right.

The water moves straight down! But it's in bursts.

But if you time the camera right you catch the bursts always in the same place, and it looks like a zigzag.

Imagine a piece of paper being pulled, and a pen wiggling back and forth. The paper (i.e. the water) moves exactly straight. But the motion of the pen (i.e. the hose) makes it look like a zigzag, but each portion of the paper only moves straight.

andrewflnr• 13 years ago

I was hoping for a standing wave too. One of the most fun things we did in physics class last semester was attach an oscillator to a tense string and try to find the tensions that would produce a nice standing wave. It's really trippy to watch a string rise up into a stable wave right before your eyes, no frame-rate tricks required.

tolmasky• 13 years ago

Do our eyes have a simplistic frame-rate thus allowing us to reproduce the effect "in real life"?

badgar• 13 years ago

Unfortunately no, our eyes don't have a simple "refresh rate." Instead, you'd have to control the light to arrive at the eye at the right frequency - which you've likely experienced through strobe lighting.

jeremyswank2• 13 years ago

Our eyes don't have a 'frame rate' at all. Light falls on the retina continuously and is continuously processed, if I understand correctly.

waynecolvin• 13 years ago

The naked eye is subject to persistence of vision but if you wanted to see strobe effects in person either a strobe light or spinning wheel with view gaps could be used.

okamiueru• 13 years ago

A strobe light set to the same frequency should allow to see the effect with the naked eye.

seanalltogether• 13 years ago

Do you have to do something special with the camera to turn off motion blur and simply take snapshots in order to achieve this effect?

panic• 13 years ago

Kind of. From the description in the YouTube video:

Set up your camera and switch it to 24 fps. The higher the shutter speed the better the results. But also keep in the mind that the higher your shutter speed, the more light you need.

Motion blur isn't something you "turn off" -- it's the natural effect of light being collected over time. The faster the shutter speed, the less time the camera spends collecting light each frame. That means both less motion blur and a darker image.

nostromo• 13 years ago

This blew my mind even more because the water looks completely frozen: http://www.youtube.com/watch?v=mODqQvlrgIQ

I'm still amazed that the water comes out so uniformly.

justjimmy• 13 years ago

Oh come on, you can't show that video w/o filming what happens when you try to touch the stream!

*The reverse flow is quite mind boggling :O

ChuckMcM• 13 years ago

A much more interesting effect is putting water and cornstarch on a woofer connected to an oscillator [1]. No special camera tricks required!

[1] http://www.youtube.com/watch?v=3zoTKXXNQIU

kbenson• 13 years ago

It seems someone else was reading What If[1] today as well...

[1] http://what-if.xkcd.com/36/

tedsanders• 13 years ago

I bet this would work much better with glycerin or glycerin/water mixtures. Water has a low viscosity, meaning it's relatively easy to induce turbulence. And turbulence, while not exactly chaotic, is somewhat random and nonperiodic.

raghus• 13 years ago

Or this http://www.youtube.com/watch?v=mODqQvlrgIQ

helloamar• 13 years ago

Awesome example. Lot of information posted on this comment, that's why I love HN.

This is What Happens When You Run Water Through a 24hz Sine Wave

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