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"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 concis
by JDGM 14y 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?
- catshirt 14y agounless 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.
- zapdrive 14y agoI think normally we process 15-16 frames per second. So if I did this with a 16hz wave, would I see the same effect?
- Dylan16807 14y agoEyes don't work like that at all. They're continuous. You can fake motion with a low rate of pre-blurred frames, but parts of perception can get all the way up to hundreds of fps.
- vacri 14y agoIf we only processed the equivalent of that many frames per second, it'd be pointless having 60Hz monitors.
- catshirt 14y agoor 24fps cameras.
- mistercow 14y agoThis is correct, although if you saw it in person lit by a strobe light flashing at 24 Hz, you'd see the same effect.
- throw_away 14y agoIt seems like it would be much cooler with the strobe, as it's easy to change it to any frequency along with the speaker frequency (compared to dynamically changing the frame rate on a camera [though, that sounds awesome]). I also wonder what the stream looks like in real life, but am amused that I cannot trust any video to show me.
- MBlume 14y agoIf you did as you said, you'd also see the length of the waves dynamically lengthening/contracting. If you saw it in person, it'd just look blurred out.
- noonespecial 14y agoA video taken at 48 frames/sec or more would begin to show you the "truth". The faster the frame rate, the more true to life it would become. This is a perfect example of a signal approaching the Nyquist frequency of the system sampling it.
- gus_massa 14y agoYes, but it's a little more complicated. With a camera of exactly 48fps and a wave of exactly 24hz you would see two intertwined jets. (It would be nice to see it. An easier implementation it is to use a 24fps camera and a 12hz wave.) With 48fps you can reconstruct any signal whose frequencies are less than 24hz (for example sin(2pit/23)+1/2 sin(2pit/17)). But the reconstruction algorithm must be implemented in a computer. The eye/brain simply "join" the nearest images of consecutive frames, so video with a 23hz signal sampled at 48fps would looks like two intertwined jets spinning slowly upwards. A computer algorithm (or a looot of hand calculations) can reconstruct the real only one jet falling down.
- 14y ago
- ars 14y agoIt'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.