Physics Videos by Eugene Khutoryansky - 2020-04-29
Why do individual atoms exert less pressure if a fluid or gas flows with a higher velocity? My Patreon page is at https://www.patreon.com/EugeneK
Thank you so much, I've a hard time "accepting" certain things during engineering instead of fully understanding it. This topic was always one of them.
Thanks. This is a problem with engineering education in general. They give you formulas, but no intuitive understanding of what is actually going on.
I must second that. While I had made the Bernoulli principle somewhat intuitive on my head (probably based on false speculations) this video really explained it by a very simple concept. Thanks from me too, Eugene.
@Physics Videos by Eugene Khutoryansky Nice video well explained in atomic dimension, this principle makes more sense in molecular dimension because the cohesion of the molecules is what dictate more. Let´s say we have heavier molecules with greater cohesion, the mass of the molecules would tend to go down at 6 o'clock of the pipeline and bigger the vessel to hold the mass higher the pressure will be, that´s why the larger the diameter has higher pressure and since the flow has to be the same, velocity increase where the volume is smaller. The less cohesive the fluid is, the bernoulli law start having issues because of the gaps between the molecules that allow them to be brought together by any applied force, this is called compressibility, in fact the lower the density more compressible is the fluid. Therefore, flow of gas has additional factors to take into account. As an example a highly compressible gas would expand from a lower diameter to a higher diameter, this is called Joule-Thompson effect in which the pressure and temperature of the gas would decrease. Summing up, it depends on the type of fluid to analyze the bernoulli law for flow in pipes.
@Physics Videos by Eugene Khutoryansky i agree; its unfortunately the case with a lot of the sciences. I really appreciate that your videos help me understand what would otherwise be memorized and forgotten :)
I thought what was going on was that cross section of water, or the plug (I think some refer to it as), was simply spread out over a greater surface area of the smaller pipe per unit of time, and the pressure per square inch per unit of time was lower. I am not an engineer or physicist.
There it is the difference between knowing something and understanding it well.
Exactly !!!! Most people don't want to understand, they want to be told that they understand due to the extremely lazy system of education.
I joined mensa after reading this comment
@Vendicar Kahn
Hmmmm....
1 : Pressure is pressure. You can measure it relativly to a reference (differential pressure) or to an absolute 0 (absolute pressure). "Y" having a negative differential pressure (relative to "X") also means that "Y" has a lower absolute pressure than X. Both differential and absolute are related. Your statement is non-sense. You cannot have X/Y differential changing without at least having absolute X or absolute Y changing either (or both).
2 : Bernoulli's principle is about incompressible isentropic flows (but can be extend to any flows). It states that if a fluid is going from area A to area B and without any form of external intervention, its sum of energies remains constant. Thus, if between A and B the flow is going through a narrower section, speed in this section needs to be high to conserve flow rate (fluid does not vanish out). If fluid changes its speed while entering and exiting narrow section, it means that there is a pressure drop to accelerate it in, then pressure is constantly low on narrow section, then there is a pressure raise to slow it out back on a wider section again. It's Newton's law : a=F/m : speed change involve non-zero resulting forces. But since this is a fluid, we're working over areas and volumes, not on points, so with density and pressure not with punctual forces and masses. Then : speed change involves pressure gradient.
Pressure DOES change. You can see here, as soon as liquid is moving, pressure quickly dropped on all the pipe as the flow raises then is more slowly going down as the tank is emptying.
https://www.youtube.com/watch?v=RFIwSxMomaU
The simplified Bernoulli's equation says that p + q = p(0)
Where
p is the static pressure, the one we can measure
p(0) is the total pressure (or maximum static pressure or stagnation pressure), the static pressure you measure on stagnating fluid
q is the dynamic pressure, pressure drop due to pressure used for kinetic energy. Basicly, it's kinetic energy per volume
And since pressure is interpreted in an atomic scale as collision due to molecular agittaion. The fact that static pressure (agitation in every direction) is partially transformed into dynamic pressure (kinetic energy or... somehow "unidirectional agitation") => yes, you could conclude that in fact, on the Bernoulli's principle, flow rate (or speed) DOES altered the molecular velocity direction.
=> "The producer of this video neither knows Bernouli's principle, nor understands it. It's laughable." You're the one laughable to mock a physics professor about abslutly relevant content and writing yourself nonsense like "Hence the pressure does not change either. " about Bernoulli's Principle... Come on...
Big brain shit
@Simon WoodburyForget very true indeed
The legacy that this teacher is leaving to the world is incalculably big
Thanks for the compliment.
Me: "Ok. Sleepy time"
YouTube algorithm : "Not until you truly understand the Bernoulli principle in earnest!"
Brain*
Understanding how this works is far superior to just remembering. Thanks 🙏
Thanks.
I really struggled to understand this fact earlier. But now it makes sense and the idea is so intuitive.
.
If wish there were more than one like button.
Glad my explanation was helpful.
@Physics Videos by Eugene Khutoryansky hey, the argument here is that the particles that exit the narrow part of the tube collide with other particles, acquiring a larger velocity component normal to the tube.
However, doesn't the same argument apply when they're *entering* the narrow part of the tube?
Why does the particle wait until the end of the tube to suffer such a collision? Statistically, I would imagine that it is highly unlikely for that to happen.
Rui Campos, inside the narrow section, the molecule is colliding with other molecules which also have a large component of their velocity parallel to the pipe. If both particles start out with a large component of their velocity in the positive X direction, they will be likely to still have a large component of the velocity in the positive X direction after the collision, due to conservation of momentum.
@Physics Videos by Eugene Khutoryansky wau that makes sense. Thank you :)
@pyropulse Yes you are right, the analysis should be in molecular level not atomic.
Professor Khutoryansky, this was one of my most-awaited topic . Thanks a lot. You made my day. As for the qualities of your videos, if Richard Feynman saw your channel, he would surely have ad his students learn from your videos. This is GREAT! Keep up the work. Thanks again!
Thanks for the compliments about my videos. And I am glad that this is a topic that you wanted to see.
maan are you a jee student?
just watched your videos
they were nice
just need to be bit longer
@Pranal Ingle hi friend! I am a class 11 student but i want to pursue research not engineering. If you love my videos that is great. It really motivated me a lot few people compliment about my videos. Please subscribe to my channel if possible and I would try my best to create more educational videos if u have any suggestions my mail is there in my channel About section. Thanks a lot and pls subscribe it motivates a small YouTuber like me
This video reminded me of Feynman's musings on the difference between the rules of chess and the rules of the universe. There are rules in chess that do not naturally arise from knowing more fundamental rules. For example, en passant and castling. You could watch a million chess games that don't use those techniques, and you'd never conclude that those are even possible. Understanding more about chess is a matter of learning more rules. Whereas understanding more about the universe often involves collapsing a group of phenomena that were once treated independently (for example, temperature and pressure) into a more fundamental concept (in the case of temperature and pressure, both are just a function of the motion and mass of individual particles in a system).
I agree, he would love this.
Me: haha, I already know how this works.
<watches video>
Me: well, I learned something new today!
pozitivity
Finally understood this concept...very intuitive explanation which is rather hard to find in any textbook..
Thanks.
I've said that the graphics from, "The Mechanical Universe and Beyond" could not be bettered, even though they are 40 years old. However, I think that you have proven me wrong. Your videos and Professor Goodstein's lectures from that series are a phenomenal combination. I can imagine you redoing all of, "The Mechanical Universe", what a treat that would be!
If you are thinking of a new animation subject, may I propose, Huygen's Principle as pertaining to reflection, refraction and diffraction. Thank you for your excellent work.
jmchez Sir Eugene has already made this video titled waves and the nature of reality.
Also Total internal reflection through Huygens Principle
I m really glad to know that such great animator and Teacher combination exists.... I have been watching your video for 4 years and they never made me feel unsatisfied😃😃
Thanks for the compliments and I am glad that you like my videos.
Thank you for making the quarantine easy!
Physics is awesome!!!!
Thanks.
Thank you for another great video, I'm a big fan of your channel. Showing physics principles in 3d is a milestone in more efficient education. Keep up the great work!
Thanks. I am glad you like my videos. More videos are on their way.
Thank you Eugene Sir. Learning Physics at lockdown gives another kick in life <3
Thanks for this amazing explanation!!!! When I first saw hydrodynamics, I was very confused about this phenomenon, since I've never fully understood how the principle could be true, rather than with the poor mathematical derivation.
Glad you liked my explanation. Thanks.
Thank god, there are some people who view physics and maths in a different way.👍👍 By the way, these days wherever you are stay healthy.... love from India
Thanks. I hope you and your family stay healthy too.
"the highly unsatisfying explanation typically given" damn throwing some serious shade lol
Thrilled seeing more frequents-uploads , even though finals are upon us. Regards :)
Awesomee timing !! I was studying fluid mechanics whole week xD
Seriously you are one of the best channels in youtube not just only for engineers/scientists but for every curious person here.
Long time fan, thank you so much for your work!!
I'm trying to conceptualize a case in which an ideal gas flows through the constriction, where intermolecular interactions do not exist, since atoms are infinitesimally small and do not interact in the limit of an ideal gas. It would be interesting to explore the case in which your atoms pass freely through one another and see if the same result occurs. Interatomic interactions should not be necessary to demonstrate Bernoulli's principle.
such a counterintuitive idea but it all makes sense now! Great explanation with some great music!
Thanks. Glad you liked my explanation.
Well done. It really comes together from about 2:50 onward! I've always wondered why pressure was lower with increased velocity, and the explanations I've been given until this were pretty lame IMHO. Thanks!
Glad you liked my explanation. Yes, the alternative explanations are pretty bad in my opinion. They are good for making calculations, but bad from the perspective of trying to understand the causal mechanism. Thanks.
Thank you for your amazing physics explanation! Well done! My very best regards form Portugal.
Thanks for the compliment about my video.
I've been waiting for a new video! Super excited to see it on my feed! Thank you! Learn something new today. =)
More videos are on their way. Thanks.
Wow, amazing explanation. I'd never thought of it like that. Great video mate. Can't wait for more :)
Thanks. Glad you liked my explanation.
Thanks this looks helpful for the AP physics 2 test this year.
Woooow. Finally a fulfilling answer for that question. Thanks a lot! I feel like a finally get ride of a heavy question I had carried over for a long time.
You absolutely made my day =D !
Glad it was helpful. Thanks.
So simple, so satusfying, so beautyfull... Love it!
Thanks for the compliment. Glad you liked it.
The Lord has returned. Thank you for the video!
I love your videos. You bring a new understanding to physics and micro-chemistry to everybody on the internet, I wish we had this in school. Could you possibly do a video on Primer Fields and the bowl shaped magnetic fields surrounding galaxies / photons?
I will add that to my list of topics for future videos. Thanks.
I am studying for the MCAT, this was making me crazy, now I can breathe again.
It’d be nice if you could do a video from a similar perspective about electricity, without leaning on abstractions such as potential and focusing on what the individual atoms are doing
Kira Vincent, I hope you take this as a compliment. I apways thought these videos were narrated by a computer. Thank you for narrating! Great work!
This video is so mind-blowing!!
I hope you make this kind of video often 🤣
Great video! Now it makes more sense. Teachers usually always just teach the equations without explaining what is actually going on. I can't intuitively grasp some concepts of fluid dynamics yet. Especially surface tension, could you please make a video explaining it ?
Surface tension is on my list of topics for future videos. Thanks.
@Physics Videos by Eugene Khutoryansky Great! Thank you so much :)
What about the pressure exerted by a high velocity liquid on an imaginary section perpendicular to the walls of pipe, will it be less than that of slow velocity liquid? 🤔
Do you mean what would happen as the tube bends 90 degrees?
Fluid dynamics states that as as a fluid rounds a bend, it loses velocity and increases pressure
Likely for the same reasoning as explained in the video, as the molecules turn the bend, their forward momentum turns into a perpendicular component of their velocity
Oh okay :)
Subconsciously I always felt Bernoulli principle was somehow reversed. Thank you for bringing my subconscious to the surface with a good intuitive concrete explanation.
Glad you liked my explanation. Thanks.
First I would like to thank you for making those amazing videos. they are propably amongst the best possible visuals for complex physics, and they helped me greatly in electricity already. With this particular video, I now understand Bernoulli's principle much better, but some things still confuse me...
Starting from 2:40, you represent the movement vector of an incoming atom to show the link between it's angle and propability to enter the pipe, but you show it spinning around like if it had a constant norm within the fluid. I do not know much about statistical physics (which I assume this is), so forgive me if I am wrong, but since the overall flow of the fluid is not null, should'nt you add the average horizontal velocity to the "random" velocity? Or maybe it isn't actually important, but to me it feels like it should be, though I am not sure why.
You then explain that since the atoms that go through are mostly the ones with a moslty horizontal speed (which I understand), the perpendicular components in the narrower pipe are overall smaller.
However, since speed increases, shouldn't the norm of velocity also increase, and as such the perpendicular component too?
Thanks for the compliment. If the number of atoms per second that passes each section of pipe remains constant throughout the pipe, and if the energy per second that passes each section of pipe remains constant throughout the pipe, then the average kinetic energy per particle must also remain constant throughout the pipe. This means that the average velocity per particle remains constant throughout the pipe. The only difference would be how much of the velocity is perpendicular to the pipe, and how much is parallel to the pipe.
THANK YOU SO MUCH FOR THIS!!!! I've been racking my brains about Bernoulli's Principle for ages. Now, finally, someone has explained it in an intuitive and satisfying way.
Glad it was helpful. Thanks.
Fantastic video, and just in time for Fluid Mechanics exam in a few weeks! This was not explained at university, thank you for allowing me to understand this equation rather than just accept it
Glad you liked my video and that it was helpful.
This is so great! I love explanations based on precise cause and effect.
Can you do the Archimedes lever law? I've tried and failed to find a good fundamental explanation in terms of atoms.
I think this approach helps build a more complete intuition that can deal with the messy complexities of the real world better than can clean abstractions.
I second this request
Although I didn't explain it in terms of atoms, I covered levers in my video at https://youtu.be/leZX0GpV5W0
Physics Videos by Eugene Khutoryansky thanks for the reply! Another good video (especially like the choice of music). I still am really curious about how those laws come about from the interactions of atoms though. In case you ever run out of video ideas :)
Love you! Finally my brain has found peace! I have been struggling with Bernoulli's Principle on atomic scale for at least 8 years! I am a physics post-grad and yet I had never encountered this explanation. Thanks a lott!!
Glad my video was helpful. Thanks.
This is really cool thanks a lot for this video. I was confused by this when I first heard of it when trying to understand pressures/velocities in ducting and piping systems. The only way I could make sense of it was by imagining at first a single molecule moving through a pipe, then a couple, then ask what is pressure and what is velocity. It makes me happy to see your video and confirm I was on the right track.
Thanks. Glad you liked my video.
your videos always makes the conplex concepts easy.I always feel excited and happy to learn from you.You are a great teacher!
Thanks for the compliment and I am glad you like my videos.
I fall asleep to these videos. You've got a soothing voice, Eugene! 🤙🏼
One.Antonio35 This is absolutely true.
For me that was always simple. The reducer forces the atoms in the same direction, momentarily reducing the vector component on the radial direction. There is a localized energy loss on the reducer. There are other significant effects considering if the fluid is compressible or not compressible.
Although I know Bernoulli's principle, but this is the first time I really understand it deeply. Thank You.
Thank you so much, this principle used to baffle me for long time until i reasoned so and you confirmed my guess and visualized it too
Thanks. Glad you liked my video.
Спасибо за работу, особенно за субтитры.
Physics Videos by Eugene Khutoryansky - 2020-04-29
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Highwaymen - 2021-01-03
Is this why Reynolds number increases with characteristic diameter at a given velocity? I've used Bernoulli's principle for 40 years but it never made any sense until now.
Dixshant s - 2021-02-17
Hi, I have a question. By this explanation, if we then keep a pressure gauge at the center of the narrow pipe, with the face of the gauge facing oncoming flow of liquid, wouldnt the pressure gauge report a higher pressure than if the face was kept facing down with respect to the pipe? (Because less water will hv component of velocity facing up in narrow pipe) but since we believe pressure is isotropic, this leads to a contradiction right?
Clarification will be appreciated
Highwaymen - 2021-02-17
@Dixshant s if you point the tube into the flow you're measuring the impact energy similar to you sticking your hand out the window of a moving car. If you point the tube Downstream you should be measuring the static pressure similar to what you would see at the wall of the tube. This is how they measure the velocity of an airplane moving through the air with a pitot tube. When they measure the flow going through a Venturi which is what the physicist is describing you're looking at the static pressure at the wall.
BeActive Behappy - 2021-02-27
I'm astonishingly surprised that I got it the exactly similar way, but entirely through intuition and not the mathematical explanation! So it goes like this:
Suppose you are given the responsibility to manage a crowd of fans rushing in to meet their celebrities along the path.
Now let's say, the crowd was very obedient and moving in the direction of the line, so they could be handled easily, hence less "physical" pressure on the ropes around them. And less "mental" pressure on you 😅😅
On the flipside, suppose they were very sluggish and disobedient and were all over the place, then the ropes need higher tolerance for the higher pressure, and you need more competence 😂
Milaan Patel - 2021-08-11
Great animations. Can you also make a video explaining compressible flows through supersonic nozzle? Being counterintuitive to sonic flows it is relatively difficult to understand what happens at atomic scale.