Discussion in 'Science, Math, History and Language Studies' started by CM Mark, Mar 12, 2013.
Science! FUCK YEAH!
He's not really manipulating the water itself with the sound energy, he's shaking the hose..
I guess its still cool.
He's manipulating the hose with the sound energy. What we call "sound" is just shaking anyway.
I like that. Now I have a desire to build a fountain
that I can use that idea with.
Good thing I'm lazy so that will pass soon.
If you watch until the end, the 23 Hz wave makes it look like the water is flowing upwards.
That's an artifact of the camera. It wouldn't look that way if you were there in person. The camera moves at 24 frames per second, so 24 hertz (24 cycles per second) would make the water appear static. 25 hertz would make it seem to move 1/24th of the way each second, and 23 hertz would make it seem to move 1/24th of the way backwards each second. It's a bit hard to explain so I hope that made sense.
Grrr... Let me try to explain it better. When you vibrate the water at 24Hz, the water will go throw a cycle that has 24 distinct positions - so you could take 24 pictures where the water appears in a different pattern, but after that it will go back to pattern #1.
Now, the camera is taking 24 pictures a second, so if the water is vibrating at 24Hz, each frame of video corresponds to one of the 24 positions created by the 24Hz wave, which makes it look frozen in air.
If the water is vibrating at 25Hz, it has 25 distinct positions, so the camera takes 24 pictures in the first second, and then the first picture of the second second is position 25, so then next time around the first picture of the third second is position 24, the first picture of the forth second is position 23, and so on. So that makes the water seem to inch forward at one frame (position) per second.
23Hz is the opposite - the camera takes 24 pictures in the first second (which includes the 23 positions plus position 1 of the new cycle), and the first picture of the second second is position 2. Next time around it is position 3, and after that 4, 5, etc. So that disparity in the other direction makes the water seem to inch backwards at one frame (position) per second.
Sorta like how when you see footage of car wheels sometimes they appear to spin backwards. That happens when the frequency of the spin gets to be near the frame rate of the camera or a fraction of it (like one half but slightly less than that).
I have seen this in person as well, and it actually does appear that way in person as well. This is a case where it is not an artifact of the camera.
Also, to me the first explanation was succinct. I knew what you meant.
You can get it to do that, but in this particular case it relates to the camera due to the frequency rate. I'm pretty sure you would need a much higher frequency to get that effect with your eyes.
And the second post was more me satisfying my OCD. I think about these things and come up with better ways to explain them later and then I think my first explanation always looks stupid.
Yup. I understood the 1st answer and I'm sure at the proper
frequency you'll see that. As a kid I remember seeing them wagon wheels
lookin like they were spinning backwards out on the prairie.
What a collection of buffoonery in the comments (not here, on YouTube).
Oh. Shutter speed. Christ, I thought I was tripping.