Camera trick lets you see sound waves in falling water


From this still image you’d think the hose dispensing the water is being moved back and forth. But watch the video after the break and you’ll see the hose is quite steady, as is the standing wave of water. It’s bizarre to be sure. Knowing how it works makes cognitive sense, but doesn’t really diminish the novelty of the demonstration.

This is the second time [Brasspup] has posted a video of this phenomenon. The newest version does a great job of showing several different patterns. But even the first segment from a year ago, which has over 4 million hits, shows the water moving against gravity. We also saw a similar rig in a links post a year ago.

We’d call it an optical illusion but it’s really more of a technological illusion. The water is falling past a sub-woofer speaker which is tuned to 24 Hz. At the same time, the camera filming the demonstration is capturing 24 frames per second. As was mentioned then, it’s much like flashing a light to freeze the water in mid-air. But the flashing of the frames is what causes this effect.

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Build a real-life Escher’s Waterfall

Instructables user [GuokrDIY] has provided a translation of a detailed guide on making one of our favorite Escher inspired illusions. Unlike the previous speculated solutions to Escher’s waterfall this one manages to keep the water path coherent up until the top level. The trick of the whole setup is very carefully controlling perspective to overlap the water source and outlet.  We say water but for some reason the builder is actually using “toilet detergents” as the liquid… At any rate, the liquid is allowed to flow downhill until it reaches the fourth corner, which does not exist. The liquid actually falls off the end of the table (out of sight) and into a basin. A carefully timed pump in the basin pushes liquid up to the top of the waterfall through one of the model’s pillars, where it then cascades over the wheel.

Using sketchup to model the various structural components of the waterfall the design is fashioned out of PVC and ABS plastic, then skinned with mapped textures to ensure that everything looks coherent. The visual details are fine tuned by viewing the whole setup through a camcorder.  The hardest part of the illusion seems to be modulating power to the pump in order to time it with the liquid’s flow.

We just hope that thing about toilet detergent was a mistranslation or some kind of sarcasm from the original Chinese article.  Check out the model in action after the jump!

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How Escher’s impossible waterfall was faked

Study the image above closely. You’ll notice that physically it is an impossible object, yet this is a screenshot of full-motion video. The clip after the break shows a gentleman pouring water into the waterfall where the wheel is located. The liquid flows in a direction that appears to be uphill, then falls onto the waterwheel where it was originally poured. Ladies and Gentleman, we have the solution to the world’s energy crisis. Nope, we have a hoax and the real question is how was it done?

[David Goldman] has come up with quite the explanation. He watched the video very closely and the put together a three-dimensional diagram showing how he would build the apparatus. If you saw the movie Inception (we highly recommend you do) you will remember the infinite stair puzzle that is exposed as an optical illusion. [David's] proposed method for debunking this hoax uses a similar build that comes in four different, precisely placed elements.

We’ve got to hand it to him. That’s a brilliant theory! Of course the first commenter on the post linked above calls this out as CGI and we’re inclined to go with that answer but that’s much less fun.

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