Name: Acoustic Levitation in ULTRA SLOW MOTION - Smarter Every Day 134
Uploaded: 2020-03-26T04:02:31.000Z
Duration: 6 min 47 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

I am in Chicago. Anthony picked me up in his awesome mustang

because we're gonna film acoustic levitation.

It's single axis, which means that we only control things on one axis here.

- Any time I see an oscilloscope I get excited.

- You'll.. so the main frequency we're using again is 22kHz

What you'll be hearing are sub-harmonic around 17-18kHz.

- But I can just put a low pass filter on the audio and I can..

- I'm guessing that you cut it out, yeah.

- Turn it up.. And on the oscilloscope you'll see

the two waves from each of the two horns. [high pitched erratic noise]

- Well let's stinking levitate something dude.

And the spoon has all those slots and so sound passes right through it.

- No way. And by sound you mean pressure.

- Yeah the sound waves, which are pressure waves I mean.

But you can see the wave length spacing basically between these.

A real sound wave actually looks like this.

The bright parts are the higher pressure and the darker parts are the low pressure.

These ripples move along at the speed of sound.

When you have two identical sound waves and you line them up just right

they no longer act like waves moving across the room.

If you have a wave coming from this side,

and another wave coming from the other side,

they become what's called a standing wave.

You get a spot right here where there's a pressure flipping on and off,

and a spot right here where the pressure isn't changing at all,

If you flip this thing upright, and then you put something tiny right inside that little pocket,

you can use that air pressure to bump something up against the force of gravity.

So it ends up looking like this ping pong paddle.

The particle wants to drop but it keeps getting knocked back up

So if it works with foam it should work with water, right?

Anthony uses a syringe to balance little drops of water on top of that oscillating wave.

Just like the ping pong ball you can see it bouncing up and down.

Look at the one on the bottom, bouncing up and down trying to find its spot.

Another cool thing is the fact that if I make the water drops too big

It happens just a little too fast to see with the naked eye.

I flew home wishing I had some way of bringing together the acoustic levitation machine and a high speed camera.

I had no way of doing this, but then I got a call from Ford.

They wanted to know if I could do any sound experiments on American Idol out in Hollywood.

We have two hours with the most amazing setup I've ever worked with,

an ultrasonic levitation device and two really fast high speed cameras.

We're gonna do 20,000 frames per second with the V2511

and we're gonna do 7,500 frames per second with the V711.

I actually wanted to hang out with these guys and teach them something new about sound.

- Alright, so we're not gonna pretend like these guys don't know what's up

because we've already done a segment and they're actually..

- OK. Come over here and let's show everybody how it works.

- And when I turn up the amplitude, sound waves through the horns

will come down against each other and will make a column

where you can actually suspend liquid or things of physical..

- [laughter] Yes, that's right, that's right.

- There's an equation that dictates how big a raindrop can be, OK.

So the pressure that's on the inside of the drop is determined by two times

the surface tension divided by the radius.

- It explodes. We're recording high speed video of these drops that we're levitating,

which is the same as changing the pressure, right?

So once we do that, the pressure gets so great

that the surface tension can't hold the drop together any more

It overcomes that internal pressure and you get an explosion.

Alright I hope you enjoyed this episode of Smarter Every Day.

I'm not obligated to say anything about any product

but Ford was awesome, seriously, they let me do awesome science

on national TV and they made all that happen.

So thank you very much Ford, I appreciate that.

Also, I did not have to get a Ford Focus at the airport

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Acoustic Levitation in ULTRA SLOW MOTION - Smarter Every Day 134

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