In 15 min he described the relationship and terms in the Reynolds equations and general fluid dynamics better than my professor did in an entire series of semesters at university.
A video like this would be great to show at the beginning and end of the those semesters. At the beginning, it provides a grounded framework for all the heavy mathematical theory that is required to do actual work with fluid dynamics. At the end, it does the same thing but brings people who have gotten lost in the weeds of the theory back down to earth and reminds them of what their work has been about and how much understanding they've gained along the way.
@alinpopa Not deep enough and is a chaotic system not so random when turbulence finds equilibrium say at greater depths? Some might say the deeper you go the quieter and calmer it all becomes.
> "We can literally time travel with low Reynolds Number" "Pff what the hell are you talking about" > Unmixes dye in syrup Convulsing on the floor, foaming at the mouth
As a student of Chemical Engineering mostly done with fluid dynamics (currently at the first year of the Master's degree), it is quite interesting (and kinda traumatizing) seeing how easily can the Reynolds number be explained. Also the value for turbulent flow is any Re>2100, not Re>1000. My OCD made me write this part. ;)
He basically taught an entire semester of fluid dynamics in two 15 minute videos. Obviously, you'd have to have some background in dif eq and multivariable calculus, maybe some physics, a bunch of practice with examples and definitely some guidance in how to work those examples, but damn... :slow clap:
He seems the guy you'd meet in some illigal rave party or something lol, surely not someone you'd think is so skilled and interested in math at first glance.
Simon Dziadoń if you go to their channel and list the videos by most popular you will see all the videos that have views in the millions in fact there are many! Logically the more videos a channel has, and the longer the mean length of the videos, the fewer total views for all videos in the channel can be expected. You can’t dance to them so it’s not going to be party material
For the record, since this wasn't explained well in the video: the bit that makes NS nonlinear is not the fact that it is time-dependent. Many linear equations include time-dependence, like the wave equation, Schrödinger's equation, the heat equation… The reason NS is nonlinear is because the time derivative is a special time derivative called a material derivative, and it includes an extra term which is not written for compactness. That is why the derivative is written as Du/Dt instead of the standard du/dt; it's actually shorthand for Du/Dt = du/dt + v•∇v.
That's true. It's even worse if you consider variable density across space and/or time. Also, the second equation in the video is written only for 'u' (flow velocity along the x direction). The same equation is written twice more, for 'v' and 'w', the other two components of the flow's velocity. So overall the Navier-Stokes equations are 4 coupled non-linear differential equations with second-order mixed differentials.
I was so frustrated about fluid dynamics, so I came to Numberphile. Not only did I gained insight, but I am now sincerely interested in fluid dynamics. Your energy and love for this topic just took me. Thanks so much you made my day.
When he talked about forwards and backwards in time, my immediate thought was of that exact experiment, it suddenly made so much more sense than it already did
I always imagined Brady more like a passive observer, but now I realise that he actually asks relevant and important questions and contributes to a successful explanation
When i was studying this i could never understand why the equation sometimes was long, and sometimes small, but in this video it dawned on me. Its so very very small that it doesnt matter. Well done. I needed this video 5 years ago.
Fluid dynamics is one of those topics where you really want a physicist and a mathematician to introduce you to the topic at the same time because the parts that one discipline tends to gloss over is looked at more rigourously in the other. I distinctly remember having two fluids based courses in the same year at uni and at times it felt like they were totally different topics instead of heavily related ones due to the difference in background of the lecturers.
Yes! I've been using the Reynolds number for years now in aerodynamics, but this is the best insight I've ever gotten to why the Reynolds number allows for scaling of experimental results. Excellent video.
"I am an old man now, and when I die and go to heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids. And about the former I am rather optimistic." - Horace Lamb
Remember never understanding Re when I studied fluid mechanics. This is the best explanation for intuitive understanding I've ever seen/heard. THANK you!
The statement "Re > 1000 is turbulent" is not actually always true, it depends and there is always a transition region. For external flows Re above 10^5 is considered turbulent while Re > 2100 is considered turbulent for internal flows .
Hoping Buckingham-Pi theorem is next. When I learned about it in Fluid Mechanics, I was blown away by how versatile and powerful it is, seems fitting to discuss it to provide not only a roadmap to Reynolds number, but any non-dimensional number.
Thinking about this helped me understand the famous molasses flood of 1919, which was a lot of fluid crashing very quickly and very suddenly from acceleration due to gravity. A lot of people today thought that the molasses flood would have been "slow" because molasses typically is, but there was so much gravitational potential energy it was able to achieve a very high Reynolds number and ignore viscosity. Then, as the fluid settled, viscosity became more important from the Reynolds number lowering to near zero (zero velocity = zero Re) which is why people became trapped.
An extra μ seems to have crept into the second term on the first equation shown on-screen at 5:33. It doesn't match the one he just wrote on the paper. Also, it isn't clear how the small-Re equation at 9:24 relates to the large-Re equation on the paper at 5:29. It isn't just a case of multiplying all the terms by Re because the "pressure" terms doesn't change.
in viscous flow (low Re) the pressure is considered with (mu*U/L) from layer tension in the fluid : tension (pressure) = (mu) * dU/ dL in dynamic flows (high Re) the pressure is nondimensionalized with (ro * U^2) from dynamic pressure and bernoulli equation : pressure + (0.5 ro * U^2) + (ro * g) = constant so the pressure gradiant will be present in both
It's not quite the same pressure gradient. The above comment mentions that math. Essentially, low Re flow pulls at component of the object (car, marble, etc.) parallel to the flow while high Re flow pushes on the normal components.
It looks like bad algebra to me - you can't just choose which terms in an equation are affected by the value you're multiplying or dividing the equation by and that's exactly what I'm seeing here. I've been to fluid mechanics lectures where exactly the same thing has been paraded out in my undergrad days and it made just as little sense then. Either this is one of those 'simplifications' academics like to use to make an explanation shorter while also making it wrong (And therefore not a satisfactory explanation at all) to anyone paying attention or he's skipped some critical detail he assumes we all know. Usually Brady's questions pull people up on things like that, but in this case it wasn't even commented on unfortunately.
Okay I am a chemist and that has to be the coolest experiment I have ever seen, weirdly I have just begun a new job where measuring viscosity is important. This was really helpful to get a understanding of this new field to me.
This is the difference between being able to write down the equations and knowing what the equations mean. It's the "on first looking into Chapman's Homer" feeling, and one of the reasons this stuff can be so rewarding.
When Tom started talking about working in reverse in a low-Re situation, a light went off in my head and I was reminded of Destin's syrup video; then about fifteen seconds later, that very video was used as an example. Cool stuff!
I suddently understood when he said "time vanishes from our equations" and this reminded me a SmarterEveryDay video... I paused to watch it and when i came back i realized it was also in this video xD Perfect connection between those two, I say good job!
Since taking fluid mechanics in university, I've learned more about extreme ultra high vacuum (XUHV) systems. I would love to see a video about the Knudsen number and how it relates to viscous, transition, and molecular flow.
There's a slight error @12:40 in the video, you can't actually mix anything at low Reynolds. If you could, then it wouldn't be reversible. That experiment doesn't actually mix the dyes together, they're kept separate in different layers. It only looks like they've been mixed up.
The minimum number of grid points for a numerical solution to converge under Navier-Stokes is R^2.25 for a 3-D simulation and R^0.75 for a 2-D simulation. R is the Reynolds number.
11:57 I had the sudden flash of what the implications were, and I was screaming at the screen "Destin demonstrated this!" then of course 5 seconds later you refer to his video. Great explanation of the maths, for it to make such clear sense before you even mentioned the demo!
You can get low a Reynolds number through high viscosity OR through small length scales... which is why bacteria in water look like they are swimming in treacle (the movement of small lengths and low viscosity is like that of large lengths and high viscosity)
Simplest Reynolds number is for a periodic vortex sheet. It is defined as density x speed difference across sheet x length of period / viscosity. Roughly speaking, for Re > 500 we will see the Kelvin-Helmholtz instability. For Re < 50 we won't.
This summer, I was at a beach where I saw a notice which said that jellyfish numbers were high. I'd never heard of those, so could you do a video on what a jellyfish numbers is? Thank you.
Viscosity is still really important for high Reynolds number flows however. The fluid flowing around an object observes the inviscid shape of an object, and that's what neglecting the viscosity term will find. When viscosity is included, we the observe other behaviour such as boundary layer effects.
Takes me back to my aerodynamics classes in college. When you are building a scale model to put in a wind tunnel if the Reynold's number of the model matches the Reynold's number of the full scale then your results will scale between the two (as long as the flow of both were both either above or below Mach 1).
Amazing content... non of my professors at university could have explained it like this. I'm still stuck in this WTF moment where I regret having listened to hours of unnecessary complex phrasings with no drive what-so-ever... How can one not be in love with physics if it's explained like this, like, seriously?!?
I vividly recall my fascination with Reynolds Number when taking a course in fluid dynamics at university. It's one of the few instances in school that was so astounding, it has stuck with me. Sadly I don't believe this video did the topic justice. There are so many incredibly useful results - one such result was used in the movie Flight of the Phoenix...the model plane designer argues that his calculations are correct and that size doesn't matter. He can say this because of his use of Reynolds Number.
![NLE Choppa - Or What ft. 41 (Orchestra Mix) [Official Music Video]](http://i.ytimg.com/vi/biOFASEgSOM/mqdefault.jpg)
Full Playlist: @t
Part 1 (Navier-Stokes): @tl3M
Part 2 (Reynolds Number): @ruwY
Part 3 (River Water): @zC6Y
Who wrote the music in this video please? Specifically the marimba or something at 3:58. Thx
Ratio of inertial forces, to viscous forces. This would suggest that if you drive your car very very slowly (V
The links don't work i think.
these are still busted but the description links work for now
??
In 15 min he described the relationship and terms in the Reynolds equations and general fluid dynamics better than my professor did in an entire series of semesters at university.
What the... I've never seen a hearted comment on this channel before! Color me impressed :)
In 2 videos, he's become one of my favorite contributors to Brady's channels.
A video like this would be great to show at the beginning and end of the those semesters. At the beginning, it provides a grounded framework for all the heavy mathematical theory that is required to do actual work with fluid dynamics. At the end, it does the same thing but brings people who have gotten lost in the weeds of the theory back down to earth and reminds them of what their work has been about and how much understanding they've gained along the way.
My thought
I hope these kinds of videos more made
16:30 "But unfortunately we live in a turbulent world, and we don't understand turbulence"
damn, that was deep
Haha, that comment was before 2020 as well.. its only gotten worse!
@@freshsi165 And your comment was made before 2022...
huh.
false.
@alinpopa
Not deep enough and is a chaotic system not so random when turbulence finds equilibrium say at greater depths?
Some might say the deeper you go the quieter and calmer it all becomes.
> "We can literally time travel with low Reynolds Number"
"Pff what the hell are you talking about"
> Unmixes dye in syrup
Convulsing on the floor, foaming at the mouth
I thunk he meant, figuritively.
l.u.y.b.q.
I get that you're joking, but how tf is unmixing going back in time???
@@SoumilSahu Entropy
Second Law of thermodynamics: *are you sure about that*
@SCP 055 yes.
Love Toms energy and enthusiasm he has for his area of study. Definitely a welcome addition to the channel!
100% agreed !
Yeah they should expand the channel to have physics added and explained. With this kind of energy and emotion this would prove very educative.
You are a 3b1b fan
But this is not a numberphile subject anymore, it should be posted in the 2nd channel
@@Dionisi0 Ofc it is. Numberphile covers all sorts of maths, not just pure maths
As a chemical engineer, this is giving me Vietnam-style flashbacks of junior year
bruh what's the Prandtl number of this times the Nusselt number of that times the Grashof number times the Sherwood number ? Schmidt? Rayleigh? 😓
As a student of Chemical Engineering mostly done with fluid dynamics (currently at the first year of the Master's degree), it is quite interesting (and kinda traumatizing) seeing how easily can the Reynolds number be explained.
Also the value for turbulent flow is any Re>2100, not Re>1000. My OCD made me write this part. ;)
@@lucianoosinaga2980 2
@@lucianoosinaga2980 years of therapy gone beacuse of the single youtube comment
@@MrDarkrai100 But to be out of the transitional regime and have a fully turbulent flow you need something more like Re>4000
This guy seems like the James Grime of engineering mechanics.
He's as excited about fluid mechanics as Cliff Stoll is about Klein bottles
@@Cliff86 i don't think anyone can top cliff stoll
He basically taught an entire semester of fluid dynamics in two 15 minute videos. Obviously, you'd have to have some background in dif eq and multivariable calculus, maybe some physics, a bunch of practice with examples and definitely some guidance in how to work those examples, but damn... :slow clap:
He also has a series called Equations Stripped if you're interested...
He seems the guy you'd meet in some illigal rave party or something lol, surely not someone you'd think is so skilled and interested in math at first glance.
I'm just so happy a channel like this has subscribers in the millions.
But views are not in milions
Simon Dziadoń if you go to their channel and list the videos by most popular you will see all the videos that have views in the millions in fact there are many!
Logically the more videos a channel has, and the longer the mean length of the videos, the fewer total views for all videos in the channel can be expected.
You can’t dance to them so it’s not going to be party material
@@druariel i know, i just gave you a fact
whooosh
??
I love how mathematicians (at least the ones shown in this channel) have this everlasting awe and happiness about the subject
@@MathswithMuneer sweet channel brother! subscribed :D
For the record, since this wasn't explained well in the video: the bit that makes NS nonlinear is not the fact that it is time-dependent. Many linear equations include time-dependence, like the wave equation, Schrödinger's equation, the heat equation…
The reason NS is nonlinear is because the time derivative is a special time derivative called a material derivative, and it includes an extra term which is not written for compactness. That is why the derivative is written as Du/Dt instead of the standard du/dt; it's actually shorthand for Du/Dt = du/dt + v•∇v.
That's true. It's even worse if you consider variable density across space and/or time.
Also, the second equation in the video is written only for 'u' (flow velocity along the x direction). The same equation is written twice more, for 'v' and 'w', the other two components of the flow's velocity.
So overall the Navier-Stokes equations are 4 coupled non-linear differential equations with second-order mixed differentials.
Ya it was only clear to me because he said "acceleration". I didn't know the short-hands being used, but think of acceleration as a second-derivative
@@schizophrenicenthusiast I believe he was using the convention that u is the vector .
Sadly most science-like people are very negligent about notation, relying on context and "common usage", thanks for claryfying!
Navier-Stokes For The Win!
And Mr. Crawford's enthusiasm is infectious.
As someone currently in a Fluid Dynamics course... this was incredible. You gave me an entirely new, and very valuable perspective. Thank you.
Thanks Nick, that's great to hear.
I was so frustrated about fluid dynamics, so I came to Numberphile. Not only did I gained insight, but I am now sincerely interested in fluid dynamics. Your energy and love for this topic just took me. Thanks so much you made my day.
That Smarter Every Day experiment was incredible before, but now it blew my mind seeing it in this context!
that was my first taught when he brought it up :)
When he talked about forwards and backwards in time, my immediate thought was of that exact experiment, it suddenly made so much more sense than it already did
@@BartKuipersdotcom exactly. I love the fact he used this Destin video.
@@BartKuipersdotcom exactly, blows my mind
As a meteorology major it's always great when they discuss thermodynamics or fluid mechanics on the channel
This is so much more fun to watch as an engineering student
Agreed. As someone currently taking Fluid Dynamics, this video is intriguing.
I always imagined Brady more like a passive observer, but now I realise that he actually asks relevant and important questions and contributes to a successful explanation
Yes! Exactly my thoughts, he always tries to ask interesting questions which stimulate thinking about the topic.
He represents us very well
"Big whirls have little whirls,
That feed on their velocity;
And little whirls have lesser whirls,
And so on to viscosity."
When i was studying this i could never understand why the equation sometimes was long, and sometimes small, but in this video it dawned on me. Its so very very small that it doesnt matter. Well done. I needed this video 5 years ago.
Fluid dynamics is one of those topics where you really want a physicist and a mathematician to introduce you to the topic at the same time because the parts that one discipline tends to gloss over is looked at more rigourously in the other. I distinctly remember having two fluids based courses in the same year at uni and at times it felt like they were totally different topics instead of heavily related ones due to the difference in background of the lecturers.
I hope that he teaches. Having teachers with this enthusiasm and love for what they do is so important to get students engaged.
Yes! I've been using the Reynolds number for years now in aerodynamics, but this is the best insight I've ever gotten to why the Reynolds number allows for scaling of experimental results. Excellent video.
"I am an old man now, and when I die and go to heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids. And about the former I am rather optimistic."
- Horace Lamb
He was right too. Feynman, et al figured out QED but turbulence is still a mystery.
Remember never understanding Re when I studied fluid mechanics. This is the best explanation for intuitive understanding I've ever seen/heard. THANK you!
Low Reynolds numbers: Exist
2nd law of thermodynamics: *"Now this is an Avengers level threat"*
Holy Mother Entropy demands a sacrifice!!
Hhsahhaahhaa
false.
As a chemical engineer student, finally theres some videos that I actually know nearly 100% of everything said in them :D
haha I'm jealous
Thermo flashbacks
andrew lai Nobody is never ready for the first energy balance with reaction
Wierd flex but okay
@@henrypentz6491 makes you feel smart cause these are some smart people :D
The statement "Re > 1000 is turbulent" is not actually always true, it depends and there is always a transition region. For external flows Re above 10^5 is considered turbulent while Re > 2100 is considered turbulent for internal flows .
The Reynolds number could be said to change the scale on which turbulence occurs.
Yes, true. For example in the flows around submerged objects like spheres, cilinders, etc.
10^5 for flat plates only
lamer flow and super critical flow also muck about with this too
it also depends on the platform or conduit it is flowing in...and then these numbers are also derived empirically
these are the first few videos that are dealing with classes im taking as an aero! so grateful its during the same time im taking them
Hoping Buckingham-Pi theorem is next. When I learned about it in Fluid Mechanics, I was blown away by how versatile and powerful it is, seems fitting to discuss it to provide not only a roadmap to Reynolds number, but any non-dimensional number.
This is my favorite numberphile video so far. More of this guy and engineering math!
I love this dude. He is so enthusiastic and easy to follow.
Normally I watch for fun facts, but this has actually really helped me rethink and get a better grasp on some of the mhd I'm doing at the moment.
Man I LOVED this guy, and fluids mechanic is the coolest part of all engineering, please keep up this series!!!
Thinking about this helped me understand the famous molasses flood of 1919, which was a lot of fluid crashing very quickly and very suddenly from acceleration due to gravity. A lot of people today thought that the molasses flood would have been "slow" because molasses typically is, but there was so much gravitational potential energy it was able to achieve a very high Reynolds number and ignore viscosity. Then, as the fluid settled, viscosity became more important from the Reynolds number lowering to near zero (zero velocity = zero Re) which is why people became trapped.
So what you’re saying is that syrup is the key to time travel?
So what you're saying is lobsters are better than humans?
@@SoumilSahu yes. Yes I am
it's obvious at this point.
This guy is a really good speaker. I love his passion for this subject
This has to be the best Numberphile video!
Thank you for bringing fluid mechanics. The whole series would be nice, Mr. Crawford is great at explaining the subject.
An extra μ seems to have crept into the second term on the first equation shown on-screen at 5:33. It doesn't match the one he just wrote on the paper.
Also, it isn't clear how the small-Re equation at 9:24 relates to the large-Re equation on the paper at 5:29. It isn't just a case of multiplying all the terms by Re because the "pressure" terms doesn't change.
Kevin Martin i also can't understand how they did nondimensionalisation
He forgot to multiply the pressure by the Reynolds number. Apart from that, he made many conceptual mistakes regarding low Reynolds number flow.
in viscous flow (low Re) the pressure is considered with (mu*U/L) from layer tension in the fluid : tension (pressure) = (mu) * dU/ dL
in dynamic flows (high Re) the pressure is nondimensionalized with (ro * U^2) from dynamic pressure and bernoulli equation : pressure + (0.5 ro * U^2) + (ro * g) = constant
so the pressure gradiant will be present in both
It's not quite the same pressure gradient. The above comment mentions that math. Essentially, low Re flow pulls at component of the object (car, marble, etc.) parallel to the flow while high Re flow pushes on the normal components.
It looks like bad algebra to me - you can't just choose which terms in an equation are affected by the value you're multiplying or dividing the equation by and that's exactly what I'm seeing here. I've been to fluid mechanics lectures where exactly the same thing has been paraded out in my undergrad days and it made just as little sense then. Either this is one of those 'simplifications' academics like to use to make an explanation shorter while also making it wrong (And therefore not a satisfactory explanation at all) to anyone paying attention or he's skipped some critical detail he assumes we all know. Usually Brady's questions pull people up on things like that, but in this case it wasn't even commented on unfortunately.
Amazing video!
Can you please make this a new series and further talk about adimensionalized numbers such as Mach or Froude?
And Prandtl, and Nusselt numbers. I remember them from my ChE classes, but haven’t really used them for work....
Froude with a video of waves going up steam against the flow. I always try to explain this topic to people and they never understand
Okay I am a chemist and that has to be the coolest experiment I have ever seen, weirdly I have just begun a new job where measuring viscosity is important. This was really helpful to get a understanding of this new field to me.
I am so happy, seeing the relationships between what I watch. I watched the smarter every day video and it turns out it relates to this video
Did Destin push for this topic?
L A M I N A R
@@DisabledCreation F L O W
In all of numberphile videos, there is one common thing:
The Guest Speaks Very Well.
As a large cruise ship, I enjoy this channel.
I thought you were going to reveal Ryan Reynold's number. Ladies would've been happy with that.
Yeah, "the ladies" 😉
Same
This is the difference between being able to write down the equations and knowing what the equations mean. It's the "on first looking into Chapman's Homer" feeling, and one of the reasons this stuff can be so rewarding.
When Tom started talking about working in reverse in a low-Re situation, a light went off in my head and I was reminded of Destin's syrup video; then about fifteen seconds later, that very video was used as an example. Cool stuff!
So glad my family contributed to mathematics!
I suddently understood when he said "time vanishes from our equations" and this reminded me a SmarterEveryDay video... I paused to watch it and when i came back i realized it was also in this video xD
Perfect connection between those two, I say good job!
Getting me so hype for my second year of mechanical engineering!!!!
Great video. His passion was extremely infectious. Helps me to keep pushing through with this maths degree
Amazing. I knew nothing about fluids and suddenly I wanna know more!
You explained it way more simpler then many bloggers
As a swimming fish, I enjoy this channel.
Hold my treacle-covered marble
"If you have 5 bananas and you give me 2, how many bananas do you have left?"
- "Are we talking bananas or potassium?"
K
That's easy, because the units remain the same...
7:49 made me really happy for some reason. That was like magic!
same!
I love this guy's enthusiasm
It'd be really fun to see more videos on dimensionless numbers in the future!
That was so cool when you finally understand the syrup colour thing because how the equation works!
I am a civil engineer so I learned this in school but pfff this teaches you how easy it is to forget stuff.
the genius of this video is the constant asking of basic questions. brilliant
Having a fluid mechanics test soon, this gave me powah! Thanks for the knowledge and enthusiasm!
Every time I watch your video, you really enjoy your job. Thank you for your explanation!
My little Hydraulic Engineering Heart is bursting with joy ❤️
I love it that how passionate he seems talking about the subject :))
I, a fellow Reynolds, am touched.
Since taking fluid mechanics in university, I've learned more about extreme ultra high vacuum (XUHV) systems. I would love to see a video about the Knudsen number and how it relates to viscous, transition, and molecular flow.
Dopamine for science students experiencing the low Re experiment
Very good idea Brady. I never thought I'd find fluid dynamics this interesting
I love all the Numberphile videos which are on the same topic as Sixty Symbols videos, but a totally different perspective.
There's a slight error @12:40 in the video, you can't actually mix anything at low Reynolds. If you could, then it wouldn't be reversible. That experiment doesn't actually mix the dyes together, they're kept separate in different layers. It only looks like they've been mixed up.
I bet his parents told him nobody would take him seriously with those piercings and now he works at Oxford
As a moron, I enjoy this channel.
Yes! Glad to see this back, love his enthusiasm!!
This is fantastic, Thomas. You just saved me a lecture.
Thanks Barton!
Awesome explanation and supporting experiment, and lots of enthusiasm.
The minimum number of grid points for a numerical solution to converge under Navier-Stokes is R^2.25 for a 3-D simulation and R^0.75 for a 2-D simulation. R is the Reynolds number.
11:57 I had the sudden flash of what the implications were, and I was screaming at the screen "Destin demonstrated this!" then of course 5 seconds later you refer to his video. Great explanation of the maths, for it to make such clear sense before you even mentioned the demo!
As a "insert job title", I enjoy this channel - has become my new meme format.
We live in a turbulent world ain't that the truth
"The universe has no obligation to make sense to you." - Neil deGrasse Tyson.
More engineering videos like this please!!!
Put in layman's terms like that helps so much.
Such a beautiful body of math and interesting experiment. This guy is awesome.
I just watched your three part series on fluid dynamics... Making tea with milk and honey will never be the same again 😛
It's nice to see people excited about what they do!
So happy to learn from a guy with passion. Its next level
this guy looks like the lead singer of an early 2000's pop punk band and I like it
Saaaaameee
“If it needs to be invisible...”. I like the Drax reference.
You can get low a Reynolds number through high viscosity OR through small length scales... which is why bacteria in water look like they are swimming in treacle (the movement of small lengths and low viscosity is like that of large lengths and high viscosity)
So satisfying that the units all cancel out
Smarter Everyday crossover 😯
Simplest Reynolds number is for a periodic vortex sheet. It is defined as
density x speed difference across sheet x length of period / viscosity.
Roughly speaking, for Re > 500 we will see the Kelvin-Helmholtz instability. For Re < 50 we won't.
This summer, I was at a beach where I saw a notice which said that jellyfish numbers were high. I'd never heard of those, so could you do a video on what a jellyfish numbers is? Thank you.
Doesn't that just mean that the number of jellyfish is higher than normal? Or is this a joke I'm entirely missing, and if so please explain
@@megallina1
I'm sure it does mean that and, yes, I was joking.
Viscosity is still really important for high Reynolds number flows however. The fluid flowing around an object observes the inviscid shape of an object, and that's what neglecting the viscosity term will find. When viscosity is included, we the observe other behaviour such as boundary layer effects.
Takes me back to my aerodynamics classes in college. When you are building a scale model to put in a wind tunnel if the Reynold's number of the model matches the Reynold's number of the full scale then your results will scale between the two (as long as the flow of both were both either above or below Mach 1).
Doing research on Chemotaxis, your explanation is wonderful and really helpful.thanks
Amazing content... non of my professors at university could have explained it like this. I'm still stuck in this WTF moment where I regret having listened to hours of unnecessary complex phrasings with no drive what-so-ever... How can one not be in love with physics if it's explained like this, like, seriously?!?
Thanks Kilian, I'm glad you enjoyed the video!
"In a highly viscous fluid, you can *literally* time travel!"
...
i think i know where all the bad popsci articles come from
I vividly recall my fascination with Reynolds Number when taking a course in fluid dynamics at university. It's one of the few instances in school that was so astounding, it has stuck with me. Sadly I don't believe this video did the topic justice. There are so many incredibly useful results - one such result was used in the movie Flight of the Phoenix...the model plane designer argues that his calculations are correct and that size doesn't matter. He can say this because of his use of Reynolds Number.
"Unfortunately, we live in a turbulent world" with only three dimensions