I Made a Lens, But for Sound

[@SteveMould]

I forgot to say "refraction" at any point during this video! So yeah... "refraction". Thanks for the idea Zach!

[@yit6]

you did at 1:30! kinda

[@davemarm]

I don't think you got the explanation right. The reduced volume effect is due to the impedance mismatch between air atoms and lower weight helium atoms which muffles the sound from one side of the balloon to the other. The "lensing" effect you're noticing is just from the air path going around the balloon meeting at a point on the opposite side.

[@davidbergmann8948]

I loooove you, Steve haha 🍄

[@manipulativer]

Please, research Nikola Tesla and how he wanted to transmit power through Earth. He was against radio:"The Hertz wave theory of wireless transmission may be kept up for a while, but I do not hesitate to say that in a short time it will be recognized as one of the most remarkable and inexplicable aberrations of the scientific mind which has ever been recorded in history." I posted a comment with another quote that is relevant. rozenrot and fallenstein (encripted) stole Tesla's technology, funded medicine, spread lies about holistic medicine... spread lies with media with onestein with relativity which Tesla disagreed greatly. And even he announced in 1920 that there must be an aether. Also Nikola Tesla's hairpin circuit shows this phenomena... there is no electrons flowing but "pressure mediation" and in nature when pressure mediation occurs its always a vortex motion. Similary a magnet is not lines of force but aether vortex flow that follows right hand rule. quantum=aether and statistic is there as its upside down where they leave the effect of aether out and wonder the statistical aspects of it all. Also the outter shell of atomst MUST be sweeiming in aether, yet we only focus on matter. If i stand correct Nikola Tesla said that matter gains its energy from outside... he also explained how capacitance changes with altitude. And time relativity is literaly the effect of the aether on the aparatus... time goes the same is just the speed and gravity that influences it all... similary a gravity clock would tick slower on the moon. Also moving muons might get more energy from the aether thus existing more time in accordance to the formula. We dont need radio, we need true wireless.

[@plasmaburndeath]

Steve would you know anyone that could do what you did on the sound side to Optical phenomena? Attempting Brevity here: I have been working on a Hypothesis about Dyson Swarms for last few years, and have pretty good grounding. But lack the Maths knowledge to formulate or put forth an equation of what to look for, to attempt to check existing databases for signs that should be present. Thanks.

[@ProjectPhysX]

Next video: acoustic lasers, using modulated ultrasonic speakers

[@GaryBickford]

A decade or so ago some scientists did this for an underwater "sonic laser". It was thought to be impossible but they used the far field optical equations to determine what such a thing would need to do to accomplish the desired results and built it. It worked!

[@omri9325]

Even better "I made a fart, but for light."

[@simeondermaats]

CodeParade made a video about exactly this! kzbin.info/www/bejne/l3PHh5mLo7hgpq8

[@hellelujahh]

What would be the equivalents of excitation and re-emission for sound waves?

[@joshzwies3601]

ProjectPhysX, Is that the same as a Long Range Acoustic Device (LRAD)?

[@YPOC]

Just today I read an article about sulphurhexofluoride, which is today's most potential green house gas in use. Until 2005 it was used in sound dampening windows panes. I wondered how it works, but didn't bother to look further into it. But now with your video it suddenly came to me that the heavy SF6 leads to total internal reflection between the glass panes, therefore converting the sound into heat. Amazing coincidence!

[@CodeKujo]

In the case of the window sound reduction, it's actually a case of impedance mismatch. You'll only get total internal reflection at certain angles of incidence. Check out kzbin.info/www/bejne/oKmyq6OGf8ehiqs for a great explanation/demonstration.

[@YounesLayachi]

@@CodeKujo good insights ! I love me some physics trivia

[@killer13iii]

there`s also Adam Savage kzbin.info/www/bejne/gJutgIZmd9WapK8

[@buddyclem7328]

@@killer13iii "It's scientific!"

[@VoidHalo]

Yeah I always love it when I wonder about something, then a day or two later I stumble across a KZbin video about it.

[@verchojanskij]

Oh gosh ! It opens up so many possibilities. I'm thinking : can we make a sound prism ? That could be a way to do some kind of physical Fourier transform. Idk, my knowledge is lacking in this field.

[@kanucks9]

Well, physical Fourier is dinner than that, you just need a set of pendulums on springs, weighted differently. They used to sell these - there's an AVE video that shows one. Fun fact: your ears do physical Fourier transforms in the same way, the hairs that vibrate and create the electrical signals are each tuned to a frequency.

[@verchojanskij]

@@kanucks9 Yeah I thought of this video too after I wrote my comment. I don't know if Fourier transform is the correct term, but what I was thinking was more similar to the way you do spectroscopy with light, but applied to soundwaves.

[@hellelujahh]

This is a great idea! A prism experiment could also help validate the explanation behind this phenomenon, ie. show if it can plausibly be a lensing effect rather than other theories that people put in the comments.

[@lazyartist2358]

Doriane Poiret I’m just commenting to see where this conversation will go. I’m also curious about this phenomenon.

[@verchojanskij]

Quick google search on "acoustic prism" and apparently some people did research on this topic at the EPFL (federal polytechnic school of Lausane) in Switzerland

[@SangheiliSpecOp]

You are a dedicated man. I loved the explanation of the slower to faster wavelengths and the shapes of the lens that you showed. Everything you were saying instantly clicked in my head! What a cool experiment

[@matthewyabsley]

Steve's wife: Shall we sort the garden out. Steve: Yeah, gimme a minute.

[@35571113]

@@Produkt_R Being payed for what you do lets you get away with lots of things...

[@Raphael3032]

it's simple, you SUCC

[@Mikaflint]

5:47 You´re such a troll i love it

[@Fruitysfaction]

the accent aigu strikes again

[@YounesLayachi]

Reversed footage ! Damnit I knew that would never worked but didn't care enough

[@gustavoexel5569]

I hadn't even noticed

[@RockySmithsen]

I stopped paying attention to rest of the video because I was trying to figure out how he actually did it (Until I saw the tape) But a better way would be to put a string on the tip of the unbent pipe, insert that tip into the balloon while holding the string. Then you pull on the string to bend the pipe to fit the balloon as needed.

[@calinguga]

@@RockySmithsen i can guarantee that can't work. even soft copper would at best kink when pulling on just the end, assuming you can even start since at first you'd be pulling parallel to the bar. to offer an alternative, i imagine you could bend it by hand through the mylar little by little. depending on geometry you might even get away with prebending it and inserting it through the hole lengthwise in a helical motion

[@vladthe_cat]

4:04 my brain: "how do you make concave balloons?" "Blow concave breaths"

[@gustavoexel5569]

You could actually use the wire frame that Steve used in his, but use two apart from one another, and actually suck air out of the baloon.

[@GamingClubGermany]

404 brain not found..... Sry

[@hydrobyte4844]

liked that reference yeah, ive made a square balloon because i blow square breath

[@harrisidh]

if I can make a flat balloon by blowing flat breaths, I can definitely make concave balloons

[@dabj9546]

@@gustavoexel5569 Also you would get a lower acoustic density

[@ScopeofScience]

That was way cool. Thanks Steve!

[@thecertifieddoctor]

i don't know why this comment is so funny

[@jakovsaric9492]

Can you expand on the project? Try and make a "beamed" sound that you can only hear if you are in line with the "beam"?

[@FlyingJetpack1]

Someone named "CodeParade" have done a nice video on making his own DYI sound laser, pick the first option while searching for "Turning Sound Into a Laser" on youtube!

[@uncompetenttv9973]

This can be done, effectively, through producing variable ultrasonic waves designed to interfere in a certain area or line to result in an audible sound. Otherwise, it is extremely difficult to prevent sound waves from spreading.

[@andrewf8366]

A parabolic disc can do this, or at least something similar. A local science museum had 2 discs at up so that you could speak into one and it would be sent to the other.

[@Hallowed_Ground]

@@uncompetenttv9973 it is does with light in laser beams though, but I understand that's different and all lasers have divergence anyway.

[@ryanriverside]

They have something like this at the Museum of Science and Industry. It's massive, and you can hear the person at the other focal point whispering, despite it being a loud museum full of people murmuring. www.msichicago.org/explore/whats-here/exhibits/whispering-gallery/

[@CronaTheAwper]

I mean you wouldn't be lying if you said click the link for 30% off

[@jamiequinn5553]

@@barongerhardt Yeah, but the S&H fee is like 600% of the purchase cost. Gotta be careful with that.

[@quesoestbonne]

Roll up ladies and gentlemen. Not full price, Not two for the price of one, But two for the price of three!

[@cavvieira]

So... How does a free and open source project pays for advertising? And why?

[@carlosprieto2231]

Carlos Vieira just like VPNs... data collectors... just a wild guess

[@adrianordp]

@@carlosprieto2231 my guess is that it has something to do with "Brave Rewards". Check on google for more details.

[@joshmckinney3254]

I found this video interesting and honestly encouraging. I never felt like I was very adept at studying physics in school or even in college, but I always wanted to be an engineer. It's explanations like this that lay out exactly how and why it works that has built my confidence to be an engineer in the aerospace industry today. Not once did you say "Snell's Law"; you just showed the behavior step by step, and that's how I learn best.

[@lexscarlet]

"ironically, it sounds just like a balloon deflating." Simon Cowell, is that you?

[@imveryangryitsnotbutter]

What are you talking about? Simon Cowell is the king of the beavers.

[@thai-cheese]

"I skewed the whole noice towards a higher frequency" ... So, a blue noice?

[@JosiahMcCarthy]

That's what I thought... Another science KZbinr had a video about this a few years ago... I can't remember who. Maybe VSauce actually...

[@christopherellis2663]

Noise 🐿 nuece there is no "noice "

[@imveryangryitsnotbutter]

Noice. 👍

[@JNCressey]

kzbin.info/www/bejne/l2nGZqqjmrR_b9E

[@ruy_mascarua]

A blue noise would correspond to high pitch frequencies :3

[@pdr-vo7fr]

U make such good content mate :)

[@Technichian462]

Here's something about sound I learned in the Air Force, working on the flight line with dozens of running jet engines all around me. If I were to stand directly in the exhaust (in this case, its about 30 feet behind an F-4 Wild Weasel, at idle, with outside temp of about 20 degrees F) I could remove my hearing protection and not be bothered at all by the sounds of the other jet engines nearby. Stepping out of the exhaust and into the cold air would cause hearing damage. The jet noise on the flight line is about 130 - 140 db at idle. But on a cold day, in the exhaust, its about 65 db. A very big difference.

[@notactuallyarabbit7546]

I greatly appreciate how you not only explain the concepts, you also explain why and how those concepts work in terms the average person can understand. Technical jargon makes it hard for the layman to understand concepts. If everything was phrased in an easier way, I think there would be far more advancements made. Cheers Steve

[@dorgodorato]

The KZbin channel Tech Ingredients goes pretty in depth with what's happening here in his video titled "Helium vs Noise." It's interesting how the kinetic energy and the different masses of air molecules as the sound wave travels through is lensed just like lightwaves.

[@alptekinakturk4185]

best quarantine activity is watching your videos. thank you.

[@bryandraughn9830]

Recording music has been part of my career as a musician and I've learned about a speaker being wired up as a microphone in order to enhance certain frequencies. I haven't tried it yet but it just seems like a really cool idea. Great video man!

[@sapiense-science-cerveau]

They are both same kind of transducers so technically yes, but it's definitely not efficient by design

[@spicemasterii6775]

"Oh that thing? It's a youtube play button. Yeah. Got one of those?"

[@SteveMould]

Oh that thing? Just what I had laying around.

[@recklessroges]

It was a good flex.

[@Noone-of-your-Business]

No need to watch this. Just seeing the thumbnail blew my mind. Of course! It's so obvious once someone points it out! Different density mediums, refraction, all the good stuff. What a great idea! This might even find practical applications. Kudos!

[@SquintyGears]

Honestly the more videos you make the more i feel like you're ending up on everything Vsauce used to do and forgot and now they only do random useless things. I love your stuff, it's both incredibly obvious from what school taught us in middle/high school but they also never bother to cover the wider meaning this explores, and thus we never notice this can even exist.

[@MinecraftLiqid]

Yea like actually releasing videos

[@darengauthier522]

I feel like vsauce is only a propagation tool.. I don't like comparing good quality non propagation tools, with propagation tools

[@ViratKohli-jj3wj]

Vsauce is not useless, you're useless

[@stephenc3060]

Exactly the perfect kind of information I'll probably never find a use for, but somehow don't know how I ever lived without! I can already see my loved ones' boredom as I try to explain how awesome this is! Liked, subscribed, all that!

[@Rottondude2]

This reminds me, my dad showed me just the other day that a campfire's smoke warps and muffles sound (such as that from a radio) quite a suprising ammount

[@areadenial2343]

It's probably not just the smoke, but the density difference as well. After all, a roaring campfire creates a big plume of hot air, which is of course less dense than cold air.

[@DFPercush]

I wish I could remember who did it, but there was a video where someone fired a vortex cannon through an artificial rain shower, it loses a surprising amount of energy. The point was why rocket launches have all that water spray, it's actually to reduce the sound, because it's actually loud enough to damage the rocket without that. I guess it's just any time you have lots of small particles with a different density, of course the hot air thing too.

[@pedrova8058]

that´s refraction due to impedance mismatch. Changes in t° of the air change speed of sound, so the waves deviate when passes trough layers of air with different t°s. . (hot air in free space is less dense ( hot put more "space" between atoms, forcing air to expand, like any other gas), so speed of sound increase )

[@richsackett3423]

I think you're wrong entirely. It's not a lens at all. It is two parabolic reflectors pointed at one another. Because the helium filling is lower density than the surrounding air, sound is transmitted more poorly, with a damping effect. If you reduced mass to a vacuum, sound would not transmit except through the skin of the balloon. Rather than a lens, it's an acoustic absorber and a very effective one. A great design I hope to use.

[@MeepMu]

Some of the loss of volume from the helium might also come from impedance mismatching, like you've covered in some of your other videos. I guess that would be the case too with the CO2, so the lensing effect is definetley stronger.

[@SteveMould]

I think you're right. Good point!

[@typha]

Tech Ingredients made several good videos demonstrating this effect: kzbin.info/www/bejne/lZLClaF3r5mFr9E kzbin.info/www/bejne/oKmyq6OGf8ehiqs

[@AlanDong]

@@SteveMould I tried to do some back-of-envelope calculations to get an idea of the reflection coefficient at the air/helium interface. First, we find the characteristic specific acoustic impedance (Z_air) of air at STP. Z = density * speed of sound. So for air at STP, the internet tells me density is 1.225 kg/m^3 and sound speed is 343 m/s, giving us Z_air = 420 (nice) kg/(m^2*s) a.k.a. 420 metric rayls. For helium, the internet says 0.179 kg/m^3 and 1020 m/s, which gives us Z_He = 183 metric rayls. Therefore the reflection coefficient is (Z_He - Z_air) / (Z_He + Z_air) = ~39% reflection. That would seem to explain a pretty significant portion of the reduction in sound pressure on the other side of a helium balloon. I also calculated ~11% reflection coefficient for the air/CO2 interface, which makes the ~10 dB increase in sound pressure at the sweet spot all the more impressive! Side note: internet also says a typical balloon is barely above atmospheric pressure. Crazy!

[@feha92]

Yeah I was thinking this too. Like, the lensing clearly existed too (though I would have liked if the mic had moved back and forth too, and not only concentrically), but I can see it contributing to lower volume too.

[@PersonaRandomNumbers]

One thing that I remember being fascinated by in uni was learning about the existence of phonons -- much like how photons are "particles" of light, phonons are "particles" of sound! Or heat, depending on how you look at it. Regardless, it was really quite interesting to see something relating light and sound together again like that!

[@MonkoGames]

"heres how i got the copper pipe in the balloon" *video of him ripping the balloon in reverse* XD

[@cplnerf]

Yes!! I love Brave Browser also this was a really cool and unique video, thank you

[@Peter_1986]

I had to do a double take on that very first scene. Steve SO used that specific angle on purpose.

[@recklessroges]

me: no idea what you are on about me: aaaaah I see it now. (I think, "We don't see the world as it is; we see it as *we* are." applies here.)

[@jonathancard4466]

This is why you're great. My first thought for a heavier gas was Argon, because I know I can get that as welding supplies. But I don't have an argon tank, but I do have a fire extinguisher, and CO2 didn't occur to me. Well done.

[@jhonbus]

A large part of the silencing effect of a helium balloon is due to impedance mismatching between air and helium due to the large difference in mass between the particles in each and the resultant poor energy transefer. The KZbin channel Tech Ingredients has a great video on this.

[@michaelgussert6158]

I taught physics for several years and I have never seen this demo. SUPER well done and I can't wait to try it!

[@hi6go7]

Tech Ingredients also has a really good video on sound isolation using helium gas

[@Kamel419]

Been using Brave for a while now, love it! Highly recommended!

[@joepg2524]

Steve: *tells about brave* Me: *already has brave* Me: *clicks link anyways for those money stacks for steve*

[@davidbergmann8948]

Thank you, Joep! 🍄

[@dextertreehorn]

He don't profit from that link :P

[@supreetsahu1964]

@@dextertreehorn if enough people hit that link, maybe brave can sponsor steve again?

[@Danyllovicius]

How Brave makes money?

[@ShadabGhafar]

If brave is free, what's their business model.

[@CarletonTorpin]

Using a non-leaking balloon to focus the sound of a leaking balloon (white noise). This is one of the only times I’ve heard someone correctly point out “irony”, rather than “situational irony”. Love the experiment and information!

[@donotoliver]

here's something: even when walking with someone on gravel, i notice sound phasing/flanging when they're a few metres away. Same effect, as when you 'shhhh' at your own hand/a wall and come closer/further from it. try it out yourself, if you understood what i meant haha!

[@markschippel7974]

Awesome video! ...but two weeks too late. My physics class just finished optics. They will see this video anyway. One of the advantages of distance learning is that it is new to us so we can experiment to see what works. Videos backed by reading and exercises seem to be the way to go. So, Thank you Steve for making my job a bit easier. Stay safe.

[@Naomi_Boyd]

Tech Ingredients did two videos on the acoustic properties of helium a couple of years ago. They include a number of interesting experiments.

[@YahNation]

I wonder if I could get a live mix kind of sound with this... Ill pocket this into the deep recesses of my brain

[@5eurosenelsuelo]

2:08 Oh my god Thank you so much for showing me that

[@kajgol]

Would be nice, if it wasn't wrong... kzbin.info/www/bejne/hH3QoYGDZdiaj80

[@P_Ezi]

@@kajgol That video glosses over the Huygens diagram with an inaccurate assumption based on peaks only instead of continuous phases. The supposed fault disappears with proper continuous wave structure.

[@ghislainbugnicourt3709]

@@kajgol In my opinion this description isn't wrong. The same way the maxwell equations can explain the phenomenon by imposing mathematical constraints, you can also impose these simpler constraints ("wavefront lines must remain parallel" and "speed changes therefore distance between lines must change") to deduce the new angle. In the video you cited, they take the example of "soldiers" (photons) which we don't have to do when looking at the waves. I'm not saying it's a better model, but it works too in this context. And it's very satisfying since it only relies on geometry.

[@jaredloveless]

Brave exploding onto the scene! I've been using it for 6 months and I love it. Getting rewards for browsing privately is great!

[@alansmithee419]

My music teacher always said I was acoustically dense. Any relation?

[@evzone84]

Thank you for giving me a spectacular AHA moment. The visual explanation of refractive index made so many things clearer for me. There rest of the video was excellent and informative as well.

[@Cachicochip]

1:08 I respect that flex 👏🏻👏🏻👏🏻

[@demidevil666]

Glad to see Brave sponsor quality content like yours. I've been using Brave for about half a year now and it's the best browser I've ever used.

[@Asdayasman]

I do believe Tech Ingredients has discussed helium extensively in one of his soundproofing videos. He didn't use a lens shape.

[@cemery50]

i met a guy that was making very large optical lens using water and plastics... you are right in the frequency/bandwiths of what you are analysing...

[@darien8360]

When you said it sounds quieter I just assumed it was because of the helium being less dense than air so it doesn't transfer the sound wave as well.

[@TheNasaDude]

In order to inflate the balloon, helium must be at or above atmospheric pressure. It being lighter would just mean that the molecules would move faster since total energy must be conserved

[@lyingpancake95]

I noticed something similar happening with my desk's studio monitors. They redirect quiet sounds from around the room (e.g. air filter, snoring cat, etc.) and focus them to specific points depending on their relative angle to to the monitors' woofers. Very cool!

[@wojtek4p4]

The thing I find interesting is that the waveform after passing through the focusing lens seems to have some distinct peaks and troughs. It's hard to say just from a youtube video, but it would be interesting to see an actual analysis of the waveform, and why it seems to increase in amplitude only in some spots. Is this chromatic aberration?

[@funkdefied1]

That was my first thought-kind of like an acoustic rainbow. Maybe it is just resonance from the balloon cavity?

[@GaryBickford]

A very long time ago I visited the Exploratorium in San Francisco. They had a demonstration set up there, with a big balloon filled with CO2 and places on opposite sides 50 or so feet away where you could talk quietly to your friend or other visitors. It was cool!

[@it_was_my_cat]

Wait, but I thought sound travels *slower* in less dense mediums and *faster* in more dense mediums? I'm so confused.

[@davidgustavsson4000]

It's not really about weight/volume density. Sound travels faster in stiffer media than less stiff. For gasses, more density doesn't mean stiffer.

[@leocurious9919]

Its a function of a lot of things, not just density: en.wikipedia.org/wiki/Speed_of_sound#Non-gaseous_media Youngs-, shear- and bulk-modulus and Poisson's ratio as well as density.

[@hippopotamus86]

That's the best way I've seen for explaining how lenses change the direction of light. Mind blown!

[@Jellyf0x]

You might enjoy Tech Ingredients video on helium.👍

[@tristandothumedotca]

Yah specifically he shows that you get ridiculous levels of sound isolation using a box with thin walls made of helium. This isn't explained by the lens analogy since a glass box still lets similar amounts of light out. I think the impedance mismatch with the less dense gas explanation he gives accounts for nearly all of the dampening effect observed in this video. See kzbin.info/www/bejne/lZLClaF3r5mFr9E

[@jomiar309]

I haven't been willing to move away from Firefox for a long time. I never went to Chrome for privacy reasons, and I appreciate these new privacy-focused browsers coming along!

[@asafattia9000]

You should have showed an air balloon for reference!

[@Richardincancale]

asaf attia And no ballon at all just to show it’s not the directivity of the phone speaker / camera mic.

[@recklessroges]

Isn't an air balloon the same as no balloon?

[@asafattia9000]

@@recklessroges well that's the theory but you should always check that in experiments

[@kourivi]

I dont quit need a browser but I'd download it with your link cause channels like you helps me more to learn, thank you mate

[@joraforever9899]

This phenomenon of noise dampening is because of impedence missmatching between helium and air. (most of it i believe) Tech Ingredients made a video about hydrogen's and sf6's sound dampening abilities.

[@walknotes]

WOW! one picture and one sentence, I fininally understand why light was bend in materials. It is so fun to watch your video, thank you for making them!

[@joejoe4games]

I pretty much switched to Firefox when Edge switched over to Chromium 'cause I'm a bit scared of a Chromium monopoly...

[@otni6115]

As a web developer I wish Firefox would switch to chromium or die out honestly. It's a lot easier to debug when every browser uses the same standards, you always get that bug that only appears on Firefox / IE. Edge switching to chromium means less tedious debugging for me and more time actually getting stuff done.

[@scoutskylar]

@@otni6115 That is so true.

[@Sauspreme]

I agree, I switched to the Dissenter browser months ago and it was extremely simple. it just pulls everything from your default browser when installing.

[@flyingby3703]

Hmmmm. There is a video about the helium thing on Tech ingredients, their explanation is a bit different.

[@Doug7oms]

Thanks for pointing out Brave browser, Steve. I've migrated from Chrome and I like it.

[@Ironypencil]

Could one possibly visualize this via Schlieren imaging?

[@achilleshiel]

One definitly could. Or actually, should

[@pilgrimonthelongroad2875]

I actually did some summer research on this subject! We were using bubbles made with sulphur hexafluoride. We didn't use white noise, but rather a shock wave. We were researching whether the shockwave (not the air flow), when focused, could break the bubble. We used schlieren imaging to show the lensing of the shockwave. I might be able to get you some of the videos we took. It was really pretty cool.

[@logdroppersavant3683]

"The intuitive one that I like involves looking at the wavefront. It's important to know that light travels more slowly in a medium with a high refractive index. So, look, as the light goes from air to glass, it slows down, and so the peaks and the troughs of the wave need to bunch up a little bit. In other words, the wavelength shortens. If the light comes in at an angle, then this slowing down of light actually changes the angle of the wavefront. And, if we assume that light always travels perpendicular to the wavefront, then the direction of travel must change as well. The opposite is true when you go from a high refractive index to a low refractive index medium. In other words, the light bends away from perpendicular - away from normal." There are a variety of reasons why such an explanation is wholly inadequate (and wrong). The reason "the peaks and the troughs of the wave [...] bunch up" is what effectively results in slowing down the speed of light through any medium, not the other way around - i.e., the peaks and the troughs of the wave are not forced to "bunch up" as a result of light slowing down. Not only does such an explanation do nothing to explain why light slows down through a medium, it has the effective chain of causality entirely reversed. Likewise, the mere act of the light slowing down alone would not provide any grounds upon which one would observe, regardless of the angle of incidence, any change in the direction of travel of the wavefront. The wavefront would appear no different, in it's linear direction of travel, than if the wavefront were traveling perpendicular / normal to the surface. At the surface boundary interface, although the lines may become slanted and change their spacing as they change their speed, they would still be oriented in the exact same direction of travel. The change in direction of travel can not be ascribed to a change in speed alone. So, clearly, planting the root cause of refraction as arising from the slowing down of light alone doesn't approach any semblance of an adequate explanation. It's the interaction between the electromagnetic wave's own electric field and that of the electric fields induced in the material by the electromagnetic wave's oscillating electric field as it travels through the medium that results in all of the observed behaviors - i.e., the slowing down of light in any medium (other than a vacuum, obviously, due to it's inherent lack of any medium) and the refraction of light at the surface boundary interface. As an electromagnetic wave - in this case, the light - travels through a medium, the electric field of the electromagnetic wave induces an electric field (the idea of an induced field interplay can be demonstrated by a magnet slug free-falling down a copper pipe) in the material that combine to form a new resultant wave characterized by a slower speed - hence, the slowing down of light in any medium. Upon exiting the medium, only the initial wave exists, resulting in the resumption of the initial speed. Likewise, the perpendicular component of the magnetic wave's electric field, normal to the surface boundary, is opposed by the induced electric field in the material, thereby reducing the perpendicular component of the resultant electric field as it travels through the medium, which yields a change in the angle of direction - i.e., if the parallel component remains the same and the perpendicular component is reduced, the resultant vector will necessarily change direction. Upon exiting the medium, the induced field no longer exists, thereby resulting in the resumption of the original direction of travel.

[@banksarenotyourfriends]

You're one of the only publishers that I actually send my Brave Rewards to. I tell lots of people that I subscribe to that they should register with Brave even if they don't use the browser, but none of them ever do - even the people that reply to my comment to say thanks don't do it. I even tell them that I've tipped them so they know there is free money there for them to collect, and nobody ever picks up the tips - So I'm going to send you 10 BAT now, partly because I love your videos, but mostly because you're not a loser that refuses to embrace change like the rest of my subscriptions!

[@SteveMould]

Thank you!

[@banksarenotyourfriends]

@@SteveMould no worries, it's not much but if you exchange it for something better in Uphold, you never know one day it might be worth something lol. I'd recommend Cardano right now and I'd have tipped you in that if Brave would let me :) All the best.

[@g-mo7130]

Nobody: Steve: *This surface here is a section of a sphere* Me: Ooh nice rhymes

[@daniellebarker7205]

This is the first time I've ever used an affiliate link for something advertised in the video. I'm loving the new browser, it's much better on RAM than Chrome. Even shared your link on my Facebook.

[@daniellebarker7205]

oh also, great video

[@bradleygonmiah7825]

Lol this is how i got the copper into the balloon. *plays video of him ripping apart balloon with copper pipe already in it... In ReVeRseE*

[@themrflibbleuk]

Giggled a little too loudly for that one.

[@microwave221]

I used to work with very large non elastic balloons for film lighting, and they had large caps on the ends which were open when deflating. If you put your arm inside and snapped, it was super muffled from how the helium attenuated the sound. It was actually kinda unpleasant to be very close to one when it was inflated, but I think that was more a result of the change in the speed of the sound reaching one ear over the other

[@krzysztofprzygudzki9209]

A imagination-stimulating way I've heard the refraction described is imagin you've got a column of soldiers - or perhaps a marching band - marching on as they go from concrete pavement to sand. On sand they will move much slower. When they approach this boundary at an angle, for each row the person most to the side will transition first and they will start moving slower. The next person in the row will then transition and they will also start moving slower. And so forth. This will skew the direction at which the entire column is moving. It will also refract on this medium transition. Marching bands are a function. Wow.

[@DeclanMBrennan]

A really snazzy demo and now we have a new riddle: "When does a concave lens focus?" How about 3D printing a concave lens that could be evacuated? Presumably you'd need to use something strong like one of Shapeways carbon materials for example and also have some internal struts which hopefully wouldn't affect the acoustics too much.

[@bexpi7100]

Another interesting thing you can clearly see on the spectrum analyzer is the frequency dependent transfer characteristic of the balloon lens. It would be interesting to see if different gases/containers have flatter frequency responses when used in this manner.

[@jimlewis1]

the angled incoming wave front to the lens was modelled as truck in my Physics GCSE lesson in 1989! One wheel hit the 'sand' and slowed, while the other didn't

[@inthefade]

I am very very surprised that this isn't used in recording studios. You could improve isolation of different sound sources from each other if recording in the same room, like a live session or something, just using large balloons and helium. Very interesting idea.

[@CjqNslXUcM]

Above some sinks, you can find an area where the reflecting sound waves bundle where you emit them. Position your head there and can hum a certain range of tones to hear them reflected very loudly.

[@benjaminsmith4058]

Coming from optics, the other reason the spherical balloon worked better is that it had a smaller radius of curvature, meaning that it could focus the sound down to a tighter point. Using the optical analogy, the spherical balloon has a higher numerical aperture. You could test this by measuring the full-width half max of the focal point and see if it is smaller.

[@-vermin-]

Another interesting experiment you can do with a white noise generator (if it is loud enough) is fire it towards a wall from a reasonable distance. Stand near the wall and move closer to the source slowly. You should hear a change in pitch as the reflection from the wall constructive and destructively interferes with the incoming waves. I discovered this while living near the beach. I noticed the sound of the crashing waves would change depending on where I stood in front of our glass sliding patio verandah door.

[@gregbell2117]

The Exploratorium in San Francisco has a great demo of this, and it results in you being able to hear your friend on the other side of the room, like the pair of parabolas you'll often find in science museums. Steve - the Exploratorium would be a font of ideas if you can get over there!

[@olivianeugeboren602]

I love videos that point out something fairly intuitive that I've just never thought of before. Its like, "oh! Of course that works!" Its neat

[@WhirligigGirl]

Another place where acoustic "optics" and normal optics meet: At the observatory I volunteer at, volunteers sometimes worry about the sound of loud running water in the dome! When the dome slit is open towards the fountain in the lake next to the observatory, from some parts of the dome you can hear the water as if you were right there. Similarly, sounds from inside the dome can often be heard by those outside. The shape of the dome is a paraboloid. There is, of course, a telescope inside. Like the dome reflecting sound, the telescope uses mirrors to reflect light.

[@SteveMould]

Nice!

[@adrianordp]

Wow. I use Brave for most than a year by now. That's a good product advertising you did. Great video as always!

[@NeoRazor]

Most notably, this is how whales and dolphins focus the sound they generate. The organ in a whale's forehead, called the melon, is a sac of fluid at a different density than the surrounding tissue. This allows the animal to produce the sound far back in the head, near their nasal cavity, and then focus the sound waves into a fine beam before it leaves their head. Having a fine beam of sound makes for better fidelity during echolocation.

[@xunxekri]

During a physics class, I had trouble wrapping my head around optics. In particular, I simply could not form any intuitions about lenses. I really wish this video had come out like two months ago, so I could have them explained to me in that signature Mouldy style. Even if it's a bit late for me, I appreciate the video.

[@arnold-pdev]

Balloons deflating and the crashing of waves. Both sound like white noise over different parts of the frequency domain. There's a physical reason for this: events happening on a continuous range of scales at random with approximately uniform energy.

[@dantarbuck]

This is so interesting. Thinking of the all the potential applications of this in a professional audio/music situation, or to sculpt the sound of a residential environment to reduce train noise etc… good stuff!

[@jaikrishchitrarasu6911]

The best visual explanation of refraction I've ever seen!

[@Andratos95]

My favorite way to make sense of why a convex lens focuses light is this analogy: imagine the wavefront as a group of people marching foreward at the same speed in the direction of the light beam, while holding hands. Now, imagine the glass as mud, which slows down the movement of these people (it has a higher refractive index than air). Since a convex lens is thicker in the middle, those people in the wavefront which are marching through it will lag behind those who are at the sides, because the latter will get out of the mud quicker since they have less mud to go through (see a pic of a convex lens to convince yourself of this). This means that if the people were in a straight line before (planar wavefront), after passing through the mud (the lens) they will march in a curve, cause the guys at the extremities of the lens will get out much before the guys at center, while still holding hands. That's why the wavefront after a focusing lens is curved! Since the people always march in the direction perpendicular to the wavefront, they will all converge into a point that's concentric to the curved wavefront (the focus)... Okay, I guess the analogy kinda sucks now cause it involves people converging into a point, but I hope you liked it 😅

[@YarxAers]

This is super fascinating! I was glued to this video while you were describing it.

[@migou1]

I noticed this phenomenon with a regular air balloon, when you approach it from your ear, you easily notice that the room background noise dampens, as you get closer to the balloon. I though it was the air absorbing the sound... thanks for this explanation. I’m thinking now, as a musician amongst other things, this could help experiment with noise blockers for microphone or noise isolation for studio room, or even for passive noise cancelling ... interesting ;)

[@1951split]

I've been using Brave for about 1,5 year now... Works like a treat... :)

[@EquinoxRebound99]

another interesting way to demonstrate this if you take 2 rocks and knock them together underwater, if you knock the rocks normally underwater the sound is negligible, but if you splash your hands down with the rocks and form air pockets underwater then knock the rocks it amplifies the sound immensely in the air pockets!

[@EquinoxRebound99]

I'd like to link a video demonstrating but I can't find one, its a trick my uncle showed me when I was young that I still bust out at pool parties

[@ytlongbeach]

Great job describing these concepts !!

[@jceggbert5]

This is the best explanation of how optical lenses work that I've every seen/heard

[@Nevir202]

Glad to see you advertising Brave, I’ve been a long time fan and use it exclusively on mobile.

[@jdgower1]

As usual, further proof that this is the most laid back, science focused channel on all of the internet. Great video.