Kelvin-Helmholtz Instability - Sixty Symbols

[@sixtysymbols]

Don't miss the extra video I made about the experiment!!! kzbin.info/www/bejne/o5fCYmdpnNB-ibM

[@chaoslab]

Always! :-)

[@Triantalex]

I missed it!!!

[@GlazeAndMaren]

I'd suggest a video on lift generated by wings. Because everywhere i look i see contradictory arguments on how it works.

[@SuperDreDo]

yep, because the assumption that the mass of air will separate at the front tip of the wing, and then meet at te back tip AT THE SAME TIME is completely wrong. It doesn't make the Bernoulli principle irrelevant here, it's just that there is more than that causing the lift.

[@zoidbergcod4]

R1D3N_1 exactly this! I've seen so many explanations that explicitly state that this is a reason why wings generate uplift, even in supposedly scientific magazines and journals.

[@treufuss-yt]

Yeah, I have seen a couple of explanations. Some using Bernoulli, some don't. In the end it comes down to force. In order to keep the plane up in the air, you need to have an upward force equal to the gravitational force. The only way to achieve this is by accelerating air molecules downwards. For this you effectively need to have a higher pressure directly beneath the wings than the surrounding air. Whether this is achieved by tilting the wing, or it's shape, or both might influence the efficiency and how you calculate the lift, but the end result is always the same. That's the explanation I have settled with. =)

[@harrisonpilling4023]

In my undergraduate course, we had a fluid dynamics unit and even it seems that the lecturer is also confused. Yes, there is some bernoulli action occurring but the principle of equal transit (ie. the air packets have to reach the end of the airfoil at the same time and thus the one which travels further does so faster) is very very wrong, and this is used to explain the airfoil mechanism the majority of the time. Look at the wing, as the air follows the top of the wing its viscosity holds it to the wing (the so-called boundary layer) and is generally projected downwards at the end of it, the air creating a force on the wing (equal and opposite to the force imposed on the air), lifting the airfoil up. As the angle of the airfoil increases, the vertical component of that force increases until there is no horizontal component - the airplane stalling.

[@harrisonpilling4023]

Yeah, I kind of had a eureka moment and said "that sounds at least somewhat sensible," so I added it. Everything else is correct as I recall but not the stalling part. I had a looksie at wikipedia and researched a little and learnt otherwise, but didn't end up editing my comment. Although if you had a rather viscous fluid, I would say the vertical-horizontal component theory would hold.

[@olekaarvaag9405]

That might be some of the most beautiful slow mo shots you've taken. Great video as always. Love cool phenomena like this that have a relayively simple explanation!

[@InnovationBlast]

Really appreciating the increased production value of these videos

[@xiaoluwang1552]

Great video and explanation. The concept of instability was well pointed out, while some other videos failed. Honored to be your fan.

[@TazR6]

What an incredibly detailed but easy-to-digest explanation. It was fascinating. I'd heard of the instability but was unsure of its dynamics. Now I know and can pretend to be clever by explaining it when I see it next. My only 'complaint' about the explanation is 'faaaarster'? Not just farster, but faaaarster. A simple faster is all that is required.

[@user-zz6fk8bc8u]

0:26 - _"OK. Call them what you like"_ lmao

[@XmarkedSpot]

Beautiful!

[@xelxebar]

In the initial description, we started with some random perturbations on the stream interface, but in the experiment the crests and troughs seem to be quite regularly spaced. Where does that periodicity arise from?

[@nicolasperalta3052]

I am impress in your confidence explaining this classic instability with nonsense arguments, please read chapter 1 of any basic book in hydrodynamic instability.

[@eqlipse333]

A good question to ask would be "Yes, but why does it appear to occur at such regular intervals?"

[@jiaming5269]

and what factors affect its periodicity

[@essayearth1354]

eqlipse333 you can prove this mathematically. There is an equation, called the Taylor-Goldstein-equation, which can have real or complex solutions. The imaginary part will lead to instability (google Richardson number). The real part is a wave, so just sines and cosines. This gives you periodicity. The instability causes the wave to break.

[@DanceSeek]

I was thinking the same thing. I don't think the Taylor-Goldstein equation answers it, the question is, why is the wavelength a specific size, not why is there a wave at all.

[@celal777]

Thanks for these videos, guys. Makes me wonder why didn't they teach us physics in a fun and interesting manner at school ?

[@huicheng3577]

Best explanation I've ever seen, excellent job!

[@shoyo4ever15]

another phenomenon beautifully explained. nice

[@billschlafly4107]

I've been to Afghanistan a couple of times. The cloud formations there were completely different to anything I've ever seen. They looked similar to the liquid in this video in that the clouds appeared to be in waved or rows. It's clear to me now that the mountains caused the strange cloud formations.

[@robbygregg4391]

what is interesting is that at 3:51, a second set of K-H instability patterns forms on the first set, and maybe, just like a fractal, a third set forms on the second set ...

[@detailed8962]

this is beautiful

[@daveThbfusion]

Different (pressure) densities have different different Mach numbers in the fluid, and the masses at those alternate densities can be thought of as two balloons rubbing against each other, balloon a has one natural frequency and the other has and the other resonates with a slightly different frequency so forming beats and the instability when the separate densities mix and witness the noise. just like Carly Simon sang about. "You're So Vain"

[@dieter2020]

Thank you! Very clear explanation!

[@kimchikoalaa714]

OMG THE EQUITRANSIT FALLACY

[@hauslerful]

Yeah I thought the same... Shouldn't happen in a 60 symbols video.

[@littlebigphil]

What?

[@EebstertheGreat]

He actually states that the air speeds up because the path over the top of the wing is longer than the path under the bottom, which is definitely wrong.

[@kimchikoalaa714]

he said 'travels further', that is not correct, I do recognise that the Bernoulli's principal does play a role in the KZ theory

[@biologistvonriemann3580]

I am so confused,some articles I have read said the Bernoulli effect as the sole explanation for why airplanes have lift is wrong.

[@user-zz6fk8bc8u]

Because it is. The angle of attack matters and lift is generated mostly by deflecting air downwards. Most passenger airplanes use the special wing forms (and the bernoulli effect) for extra lift to safe fuel.

[@fizzicist7678]

the Bernoulli equation is wrong, but effects of pressure and velocity still apply.

[@DANGJOS]

How is the Bernoulli equation wrong??

[@fizzicist7678]

it is correct for the case in which flow is steady, but on a plane it is turbulent, which Bernoulli does not deal with. Should have been more clear on that one, I admit.

[@DANGJOS]

Oh I see

[@2Cerealbox]

This going to be one of those things I see everywhere now, isn't it?

[@G36-999]

Last time i was this early the electro-weak force was still around

[@hectarsavoie8166]

Wait, has there been a huge discovery I am not aware of ?

[@biologistvonriemann3580]

Yeah,the weak force and electromagnetism can be unified into the electroweak force.Discovery of this won a Nobel prize a few decades ago in 1979.

[@biologistvonriemann3580]

I am replying to Hector comment.What do you think he was saying then ?

[@tmkc1372]

That face at 3:33 is what I live for!😂😂😂

[@ADHR26]

I'm interested in how it works in 3 dimensions, because in the tube experiment there seems to be a thinner area of material in the middle of each hook.

[@erikgoransson971]

7/10 Not a waste of my time. Glad I watched this.

[@sixtysymbols]

Not our best ever review, but solid enough!

[@SunHunter27]

A perfect 5/7 from me

[@Naijiri.]

A E = mc2 where m is a number greater than 0 and c is 299 792 458 meters per second from me

[@SG1guru]

But why do they appear at regular intervals? Shouldn't the spacing be more random if it's growing from surface fluctuations?

[@MrClivesinger]

That is a very difficult question to answer, and there are still papers being published on it. Basically, some wave modes are more unstable than others, and their stability (plus a few other experimental parameters), determines how fast they grow. You could think of all possible perturbation ripples happening at once, but only the very fastest growing waves reach the size you can see. Some waves also get an extra initial "kick" from surface and compression waves initiated while setting up the experiment, which then get a head-start, so to speak.

[@seigeengine]

What do you mean by appear to regular intervals? And I'd guess the answer is because the effect self-initiates itself. That is, one minor perturbation creates a pattern of oscillation.

[@iabervon]

If you've got a bump at one end and it's growing, the stuff in the bump has to come from somewhere, which means that a dip has to get started a little ways away, based on the size and shape of the growing bump. But when a dip is created, it also starts growing, which pulls stuff away from the top a bit further along, starting another bump, and so on. Since the instability is the same in each case, the distance to the next resulting fluctuation is the same in each case. If there are multiple bumps that happen to form before the chain gets established, you get some irregularities, which you can see in the raw slow motion attached to the extra video. Around 1:50 in that video, you can see two smaller, closer-spaced, faster-mixing bumps to the right of the bigger bumps in the rest of the shot.

[@igNights77]

I didn't know I needed a cloud fix until this video.

[@ur_a_buS]

Awesome video!

[@FurasCebulowy]

When I go outside and I see this cloud I feel like just standing there and watching it untill it disappears.

[@sragvit8014]

Hey Brady! I'd love if you could make a sixty symbols video regarding the new study published in nature on quantum communication.

[@EzraFeilden]

Great video, but this only explains how one instability forms. Why is it the case that they form with such uniform regularity (like a sine wave with a set frequency)?

[@mccutcheogeoff]

i first learned about this effect when learning why tall towers tend to wobble in the wind

[@iagocasabiellgonzalez7807]

3:33 pure gold

[@thortunge9369]

Any explenation of why the pattern is so regular? I would think, because the instabilities can start from small pertubations anywhere in the interface, that the 'swirls' should be more irregular?

[@eugen9611]

this is so cool

[@mullerman1104]

Actually I never thought these clouds would be THAT special. I live in Germany between 2 lines of Mountains, and we often have inversive weather. I have seen these quite often.

[@CristiNeagu]

2:27 Common misconception. Airplane wings don't generate lift because of the Bernoulli principle.

[@francoisdelabruch6174]

and why so?

[@majoorF]

So the horsehead nebula is actually giving us information on interstellar flows? something like that?

[@harrysvensson2610]

3:31 "LOOK AT IT, JUST LOOK AT IT!" -"I'M LOOKING AT IT!"

[@morgengabe1]

The music in this video could be sampled into one heck of a jungle track.

[@heatherstub]

!!!

[@JmanNo42]

I've never seen any wavy clouds, but i noticed i think 3 years in a row fastmoving stripy clouds in the spring. I thought it had something with lowpressure to do because they move at so lowbase? It is the only sensation of earth moving i ever experienced. Maybe it is just a coincidence or wave a really common pattern, but i noticed that greek urns often display a row of spiraling waves. They also feature the more blocky horseshaped ones.

[@JmanNo42]

It probably just my imagination but i have a feeling the ones with the wavepattern often depict wars above them, so i am not sure they really there to depict water. It may be they understood some scientific principles of cloud formation?

[@davidb2885]

2:27 But the air is only going faster because the pressure is increased - the air is compressed. So the Bernoullieffect is probably just cancelled out by the higher pressure.

[@JohnJackson66]

Ripples in the sand after the tide has gone out and sand dunes caused by the same thing I suppose.

[@JasonDoege]

What explains the regular spacing of the instabilities?

[@marior8249]

nice video

[@junak777]

Stirring movement in bartender mixing. Line | or arrow leaving behind 2 vortecies. Spiral mixing won't work in cup. Can You make one video on that subject? Thanks!

[@ChemEDan]

Why so few views on this great video?

[@OwariNeko]

Why is there such a regular distance between the instabilities?

[@BeeHolding]

Airplanes have lift because the wings are inclined planes relative to the plane of thrust.

[@SahnouneKhaled]

instabilities is one of the most exciting but least known topic of physics

[@androidkenobi]

those were the straightest and most parallel looking lines I've ever seen someone draw

[@AllanDoane]

As I watch the effect in slow motion I am curious if the instability is fractal. That is, it seems as if each "horse head" develops little horse heads. Or am I seeing things that aren't there?

[@kwanarchive]

Oh no, not the "air goes faster over the top" theory of aerodynamic lift!

[@felixwinchester9256]

if you spin a spinning top clockwise then anti clockwise..will the spinning time be same in both cases? let's assume there's no coriolis effect and the spinning top is perfectly symmetrical and of course the surface has friction.

[@esthermofet]

2:29 -- except it isn't because there are loads of aircraft that can fly straight and level with negative angles of attack or even straight and level while inverted.

[@BrunoJMR]

why does it have a well defined period? if the initial perturbations in the symmetry are random, shouldn't the bulges form at random distances from each other?

[@ununseptium7961]

So if the flow is faster on the bottom, will the clouds shown in the picture be inverted?

[@beachboardfan9544]

So in the how its done video you mention the fiddly part after its full to cap it off with no air bubbles inside.... so how would this experiments results change if there was an air bubble in there?

[@yoverale]

This is the principle behind ocean waves formation, am I right?

[@boludecesno2832]

and the distance between the waves is given by? what is producing that particulary periodicity in distance and not another? It has anything to do with the Brunt-Väisälä frequency? Cheers

[@isaaclam384]

At 2:15 why is it that the same volume of air must go through a more or less constricted section? Is it the same as the case for airplane wings?

[@codediporpal]

A Scots-Irish and a German. I'm curing how these kind of collaborations happened.

[@wood-eye]

But why does it seem to have a uniform wavelength?

[@namas000]

cool

[@Jet-Pack]

And the air on top of an airplanes wing reaches the end faster than the air below it.... Lift isn't just created not because of the greater distance, the molecules going over top or going underneath never meet again actually.

[@Davdof]

But why are the horse heads in such a regular pattern? They seem to appear at regular intervals... is there an explanation for that?

[@mikenorman4001]

Shame! Shame! Lift over a wing is not caused by Bernoulli phenomenon! It's the Kutta condition at the trailing edge resulting in circulation that is described by the Kutta-Jukowski Theory of Lift! Please make a correction video!

[@senorPFox]

Makes me sad to hear you guys repeat the equal transit/bernoulli lift fallacy. Make a video about airfoil lift!

[@beeble2003]

Ironically, the animation even shows why airfoils generate lift: you can see the air being displaced downwards behind the wing...

[@TimothyReeves]

2:35 the other ironic thing is that the airfoil in the animation is symmetric top to bottom so the path length is the same top and bottom!

[@menturinai1387]

Why the spatial periodicity?

[@wouldntyaliktono]

why does the pattern appear so regular, and why all at once? is there some relationship between the density of the two fluids and the period of the waves that form?

[@RobertSzasz]

wouldntyaliktono There is a feedback effect. The first set of ripples to form at the correct spacing (depending on the density, velocity,etc... of the two streams) make it more likely more ripples will form at the same spacing.

[@gthakur17]

never clicked on video so fast

[@Squidward1314]

Why is it happening everywhere (along the interface) at the same time?

[@Cynthia_Cantrell]

"Horse head clouds?" I think not. "Troll hair clouds."

[@ChannelMath]

It's confusing: at first you talk as if only relative motion matters (Galilean relativity), but when the upper layer is raised a bit and so constrained to go faster... isn't it only the relative speed that matters? so the lower layer is also going "faster" (relatively, in the other direction), so why isn't the upper layer pulled down?? [With the airplane wing it makes sense, since you are comparing both speeds to the same measuring stick: the speed of the wing.] Thanks!

[@JousefM]

Well, the theory of "lift" that's explained is unfortunately wrong. There's more to it than the "equal transit time theory"...

[@acerockman3520]

* looks outside * * sees one * * goes back to computer * * makes a comment *

[@UMosNyu]

But why do they all have similar lengths? Why not just one mountain and one valley?

[@youtube_username]

.

[@chattyw87]

3:23 this should be a meme

[@AV1461]

But clearly the pattern is periodic. What determines the period of the pattern?

[@rchuso]

As a meteorologist, we were taught those were "Kelvin-Helmholtz clouds".

[@MephLeo]

I'd rather call it _sweetroll clouds_, they look delicious.

[@BboyHotArab]

lol "cloud people"

[@MasterGhostKnight]

Stop saying that airplanes fly due to the Bernoulli effect, it's wrong!

[@robertlediable5435]

Did you notice that some ancient greek frieze have the same pattern?

[@y__h]

Prof. Merrifield looks.... Merrier.

[@tohtoh529]

is no one going to say anything about that fantastic beard?

[@radix4801]

Is this similar to how tornadoes are formed?

[@fizzicist7678]

Radix tornados are bizzare things, they are turbulent which makes bernoulli dodgy. however essentially yes, it is formed by the same mechanism of instability. mushroom clouds from explosions are also the result of the instability.

[@roidroid]

Anyone for a cup of Insta-Billy-Tea?

[@2manyIce]

Yes, me. Served at triple point, please.

[@flymypg]

Shouldn't that be "cuppa"?

[@Triantalex]

No, noone.

[@farzaan1479]

Why did 23 people dislike this

[@celewign]

Professor merrifeild is getting so gray... I hope he's not stressed 😧

[@Fin4L6are]

amongst cloud people :D

[@detailed8962]

i think i saw this video before

[@ghiribizzi]

0:47 jovian instabilities

[@fizzicist7678]

ghiribizzi and thousands of years old jovian vortex

[@RealRobotZer0]

Richard Muller doesn't agree with the wing.

[@laurabelford2589]

Is that why Poseidon ride horses?

[@axelasdf]

Compounding doldrums.

[@superdau]

Why is the wrong explanation of lift still around? Especially on a physics channel? Where is the law that states the fluid packets separated at the front have to meet up at the back again? They don't even in practice, so I don't know where that argument is coming from in the first place (the fluid flowing over the top reaches the trainling edge faster!). Also *a simple paper plane disproves transit time/Bernoulli argument* . Symmetric, flat air foil shape and still flies. Ever held a hand out of a driving car? Plenty of lift there. And unless you're a Dolphin I doubt your hands look like airfoils.

The new form of chemtrails, extra boron.