It is visualizing physical reality, not magic.

@@NatSciDemos you say "physics", we say "magic."

that deep whistle ? isn't that audible to all? so we are the chosen ones? 😂

I think is because the microphone can hear it so the video reproduce it on a lower frequency(the max) Excuse my grammatical errors, I'm not english

it hurt my brain..

F

I heard that loud and clear

Thanks 😊

Yes, that has been done. Of course, the wavelength is much shorter because the speed of sound in water is much greater than in air.

You would need to shoot at least 7000 frames/second .... 10,000 would be better. At that frame rate you will need an INCREDIBLY bright point light source. Doable, but not easy or cheap/

@@wolfgangrueckner7151 Something for smarter everyday ...

Our mirror is not large enough to see an acoustic double-slit diffraction pattern.

In principle one could use 10 kHz sound, but it wouldn't work very well with our setup. For one thing, our transducer is designed to work at 28 kHz. Since 10 kHz corresponds to a wavelength of 3.4 centimeters, we would want a more sensitive optical setup with a larger mirror.

I believe it would be painfully and dangerously loud.

I can hear it. It sounds like a tone generator with no vibrato playing an A natural. Sometimes it warbles between B flat and A when he sicks his hand near it. But the sound is nothing special. You can get the exact same sound by hitting an A on a piano or synthesizer.

Yes it is a concave mirror with 2 meter focal length. The light source is a white LED behind a 400 micron pinhole. Yes when the strobe frequency is exactly the same as the transducer then the image appears stationary, and when they are slightly off then we see the image animated.

Yes indeed. This video, for example, was taken with a constant point light source: kzfaq.info/get/bejne/jtZ-ldyX3d7Ph3k.html

depends on their phase w.r.t. each other

I think it would look a lil bit like at 4:18. The reflected waves are obviously the same length and therefore you can see an intereference shape forming. But i think because of the youtube video compression it looks very blurry. kzfaq.info/get/bejne/mtWod7Kd3KvGnJs.html Here its reflected directly kzfaq.info/get/bejne/Y8h_nM1l2ra1Z6c.html Here is exactly what you meant

The pressure waves that radiate from the transducer are animated by a strobing light source in the schlieren optical setup. The strobe operates close to the transducer frequency, about 28 kHz. Without the strobe, we would not be able to view the pressure waves with a normal 24 fps camera, because they move at about 340 m/s. In principle you could use a continuous light source with a high-speed camera that can operate at 28,000 fps, but since cameras like that are expensive and not easy to find, we use a strobing LED and normal-speed camera instead.

@@NatSciDemos - Your response to my questions didn't say anything more than you'd said in the video. Sound is a problem. One of those problems is the speed of the sound source vs the speed of sound; about 760 MPH. That number is tossed out as a given because sound can be measured to travel at that speed. A typical loudspeaker (and, I'm sure your 28k transducer) is likely moving at around 1 MPH. Yet, somehow, the sound takes off at a speed of the speed of sound for both, independent of the frequency. Richard Feynman, in his physics text book tries to explain it but, does it with a couple of pages of mathematical equations. Which means he explains nothing of the mechanism of how it works. But, even a hard core mathematical physicist like Feynman does get it that the equations don't actually explain the mechanism of how things work: kzfaq.info/get/bejne/ocpgq7eXydqaoas.html When a sound is generated (however it's generated) in the air (or water or solids), it spreads out. Yes, it can be "directed" but, generally the sound spreads out pretty much in all directions and becomes stronger as it spreads out. Not stronger in that it becomes louder for each individual listener but stronger in that it arrives at each listener much louder than the inverse square law falloff rate of the alternating compressions and rarefactions ascribed to sound waves are said to do. That relates to another error that's taught about sound; that it's radiated a "energy" from a sound source. Nobody either seems concerned about this massive growth of the strength of the sound as it spreads out or concerned about explaining HOW that happens (as Feynman noted). A cricket can be heard at a distance of a few hundred feet in a quiet area and can be heard by 10s, 100s or even 1000s of people (and animals and presumably other crickets). But, that cricket doesn't just vibrate the eardrums of all those people and animals. It vibrates every surface it contacts that is elastic enough to be vibrated (and echoes off those that aren't). If you add another another 10,000 microphones in that space, each one will get a full measure of the sound of the cricket as well. The reason I mentioned the Ruben's Tube is that it shows that the points (nodes) of concentrations of the gas (usually propane) occur at the holes in the tube. The nodes of compression and rarefaction at the eardrum or a microphone diaphragm occur at the eardrum and diaphragm. It's the sensing or measuring of the effect (by introducing the discontinuity, that displays the effect. Since the compressions and rarefactions can be seen in your video, I wonder what the sources of the discontinuities are that creates them. THAT was my question. If your transducer is filling a volume of some hundreds or thousands of cubic feet of air, and it's doing it with the compressions and rarefactions you show in your video, how does your transducer have the power to physically move all that air? Or is that one of those things that the geniuses of science don't concern themselves with and perhaps we shouldn't either? salaphysics.com 091822

A function generator is used to turn the LED light source on and off.

it attenuates the ultra-sound

We're gonna need a bigger mirror...

In the Ultrasonic Levitation demo, the particles are suspended in an acoustic standing wave, so animating it like a traveling wave would not be possible.

There are no such things as particles, only perturbations in the Aetheric fluid.

It's a schlieren optics setup, so there's a point source at twice the focal length of the mirror. sciencedemonstrations.fas.harvard.edu/presentations/schlieren-optics

A double slit experiment is certainly possible but it has its technical difficulties with our apparatus. First, the slits should be a few wavelengths in width and be separated by many, many wavelengths. Given that geometry, it's hard to bathe both slits with the same intensity sound with our single transducer.

We tried that with our single transducer but it didn't look very good. The problem is that the beam of the sound is narrow compared to the wavelength. It might be possible with two transducers right next to each other? In another video called "What Does Acoustic Interference Look Like?" we created interference with a pair of transducers pointed towards each other.

You are not actually hearing the 28kHz signal. It is an effect called aliasing and it is an artifact of the recording. An example: If we assume that the sampling frequency of the recording was 44kHz, the highest frequency (in the baseband) which can be accurately reproduced is 22kHz (the Nyquist frequency). Since 28kHz is outside this range you will hear an alias of the 28kHz signal in the baseband at a frequency of 16kHz. I tried to estimate the sampling rate of the audio recording. I would estimate the tone we are hearing to be something around 12kHz. This would mean that the audio was recorded at a sampling rate of approx. 40kHz. Although 40kHz is not a common sampling rate for audio equipment it seems approximately right (also I am not very good at estimating the frequency of high-pitched sounds). Although I am a little skeptical since proper digital recording involves filtering out all frequencies above the Nyquist frequency before recording it (and I would assume that a camcorder would actually do that properly). But I assume the original signal was so loud that the filter doesn't work properly.

The audible wavelengths would be too long for us to see with this mirror.

Accidentally shows how time is an illusion and how still pictures became movies, all a light field parlor trick, just need a snake oil salesman with a great pitch line.

the mirror is only 0.38 m wide

Twin towers in Chicago?? What planet conspiracy ppl come from??

World trade center twin towers were in New York City, New York.

Way to "sound" smart without actually saying anything.

It's a subharmonic interfering with the mircrophone