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When I meet God, I am going to ask him two questions: Why relativity ? And why turbulence ? I really believe he will have an answer for the first. Werner Heisenberg
I want to thank you for this explanation. This has been bothering me for 50 years and I have a BS chemical engineering and I study physics as a hobby. This is the first time this phenomenon has ever made physical sense to me.
Eugene, your explanation of why the pressure goes down in the narrow part of the pipe is not correct. The pressure in the wide part of the pipe that followes after the narrow part is still lower than the pressure in the narrow part of the pipe.
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.
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.
@@EugeneKhutoryansky 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.
@@EugeneKhutoryansky 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.
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.
@@EugeneKhutoryansky 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.
Unfortunately, this violates some very common and well understood accepted principles of physics. Charles Crummer makes the same errors, which doesn't make it correct. .. The statement at 2:07 is correct. "there is no reason to expect an atom with a higher velocity to exert a lower pressure on the walls of the pipe." There can be the same pressure in a fast fluid as a slow fluid. They simply have the same static pressure. Bernoulli is not about speed. It is about changes in speed or velocity which is Acceleration along a path. The pressure on the walls of a sealed jar is the same regardless of the speed of the jar. A fundamental flaw in this misconception at 2:42 is is that there no reason to expect a molecule to have the thermal vibration in only one dimension. These pressure causing vibrations are random in direction and are how they bounce round between other atoms. At any given instant a molecule may be going down and the next at 90 degrees or even 180 degrees to the previous vibration. That simple fact breaks this false logic. .. Then. . . It is the average velocity (over time) that has a directed motion when the kinetic energy is added to produce an increase in speed. That directed velocity is vectorially summed to the random vibrations. This is vector addition of velocities. This means that the random vibrations are superimposed onto the linear velocity along the tube. This is fundamental physics. Vector quantities like speed and acceleration add vectorially. Ignoring that fundamental physics is another flaw in this. .. .. Then, the added kinetic energy in the moving fluid is in only direction. It is not increasing the random thermal vibrations. That would require increasing the temperature. This is another flaw in this story. Moving the fluid along the pipe does not raise the temperature. Therefore, the statement at 2:23: "an atom with a higher velocity would have a higher kinetic energy and, therefore, exert a larger force on the pipe walls" is false because it conflates / confuses thermal energy and momentum in one direction. .. .. Consider bouncing a ball on the floor. Each bounce imparts some momentum to the floor. The ball's actual motion is only vertical.. Now, start the room moving (a train car) and the ball still imparts the same momentum to the floor with each bounce. It's actual motion, relative to the stationary ground changes. It has the SAME vertical component, but now a horizontal component vectorially added to the vertical motions. The pressure on the floor does not change. . However, these two motions are orthogonal and have no effect on each other. The vertical up[and down bouncing component remains the same. ONLY the ground referenced horizontal component changes as the speed increases. This physics does not change if the ball is bounced on the ground outside the train's window. . This fails on these fundamental physics errors.
@@Observ45ernothing you’ve said here explains Bernoulli’s. Furthermore, nothing said here entirely disagrees with the video’s point. Lets think about a couple of points. 1) pumping fluid through a pipe absolutely does increase the temperature. This increase in temperature primarily occurs at the impeller of the pump, but eventually, all the fluids kinetic energy is dissipated when it stops flowing, as heat. There is friction and this linear motion is eventually all converted into vibration/temperature increase. Therefore this net net movement of the entire fluid body absolutely does count as part of the motion that sums to temperature. It may not be much from the perspective of the fluid at the time until the fluid’s motion is dissipated because the molecules aren’t necessarily moving faster relative to one another. But any probe or obstructing fluid in the flow stream will experience more collisions on the flow-ward side and thus an increase in temperature. This is what limits supersonic aircraft - the temperature of the skin gets so high from the increased collisions at the leading edge. There is also an increase in pressure at the flow-ward surface for the same reason - and as we know in fluids especially gasses temperature and pressure are so closely tied. In fluids this low pressure at the vena contracta can be below equilibrium vapor pressure and cause vapor bubbles. 2) it isn’t like the pressure in a venturi drops to zero. There ARE still random molecule collisions with the pipe wall at the low pressure surface, but they do occur less frequently thus the low pressure. There is also a temperature drop at the low pressure point in gas, and in liquids if they are flashing especially. Look at a metering valve in refrigeration for example. The video is correct and you are incorrect to completely separate molecular motion associated with temperature from molecular motion associated with pressure and net fluid motion as well.
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!
@@pranalingle9424 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 RUclipsr 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.
I would love to see a video on the counterintuitive nature of supersonic flows in a converging/diverging nozzle. I think this style of visualization would serve it well, showing how the gas slows down as the nozzle converges and speeds up while it diverges.
This is magnificent ! After fifty years of unsatisfactory explanations finally an explanation that makes sense ! My professors would bombard me with formulas and differential equations but never bothered to explain what was really happening. I’m eternally grateful to you ! 🙋♀️👍🙏🏻
Thanks. I am glad you liked my explanation. Yes, what you described is a symbol of what is wrong with technical education. Everything is "explained" with equations. In other words, it isn't explained at all.
Unfortunately, Claire, this violates some very common and well understood accepted principles of physics. It repeats the same errors that Charles Crummer makes. .. The statement at 2:07 is correct. "there is no reason to expect an atom with a higher velocity to exert a lower pressure on the walls of the pipe." There can be the same pressure in a fast fluid as a slow fluid. They simply have the same static pressure. Bernoulli is not about speed. It is about changes in speed or velocity which is Acceleration along a path. The pressure on the walls of a sealed jar is the same regardless of the speed of the jar. A fundamental flaw in this misconception at 2:42 is is that there no reason to expect a molecule to have the thermal vibration in only one dimension. These pressure causing vibrations are random in direction and are how they bounce round between other atoms. At any given instant a molecule may be going down and the next at 90 degrees or even 180 degrees to the previous vibration. That simple fact breaks this false logic. .. Then. . . It is the *average* velocity (over time) that has a directed motion when the kinetic energy is added to produce an increase in speed. That directed velocity is vectorially summed to the random vibrations. This is vector addition of velocities. This means that the random vibrations are superimposed onto the linear velocity along the tube. This is fundamental physics. Vector quantities like speed and acceleration add vectorially. Ignoring that fundamental physics is another flaw in this. .. .. Then, the added kinetic energy in the moving fluid is in only direction. It is not increasing the random thermal vibrations. That would require increasing the temperature. This is another flaw in this story. Moving the fluid along the pipe does not raise the temperature. Therefore, the statement at 2:23: "an atom with a higher velocity would have a higher kinetic energy and, therefore, exert a larger force on the pipe walls" is false because it conflates / confuses thermal energy and momentum in one direction. .. .. Consider bouncing a ball on the floor. Each bounce imparts some momentum to the floor. The ball's actual motion is only vertical.. Now, start the room moving (a train car) and the ball still imparts the same momentum to the floor with each bounce. It's actual motion, relative to the stationary ground changes. It has the *SAME* vertical component, but now a horizontal component vectorially added to the vertical motions. The pressure on the floor does not change. . However, these two motions are orthogonal and have no effect on each other. The vertical up[and down bouncing component remains the same. ONLY the ground referenced horizontal component changes as the speed increases. This physics does not change if the ball is bounced on the ground outside the train's window. . This fails on these fundamental physics errors.
This is the best video explaining the intuitions of Bernoulli’s principle! I’m going to share this with my friends in my engineering classes! Thank you!
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.
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!
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😃😃
Unfortunately, this violates some very common and well understood accepted principles of physics. It repeats the same errors that Charles Crummer makes. .. The statement at 2:07 is correct. "there is no reason to expect an atom with a higher velocity to exert a lower pressure on the walls of the pipe." There can be the same pressure in a fast fluid as a slow fluid. They simply have the same static pressure. Bernoulli is not about speed. It is about changes in speed or velocity which is Acceleration along a path. The pressure on the walls of a sealed jar is the same regardless of the speed of the jar. A fundamental flaw in this misconception at 2:42 is is that there no reason to expect a molecule to have the thermal vibration in only one dimension. These pressure causing vibrations are random in direction and are how they bounce round between other atoms. At any given instant a molecule may be going down and the next at 90 degrees or even 180 degrees to the previous vibration. That simple fact breaks this false logic. .. Then. . . It is the *average* velocity (over time) that has a directed motion when the kinetic energy is added to produce an increase in speed. That directed velocity is vectorially summed to the random vibrations. This is vector addition of velocities. This means that the random vibrations are superimposed onto the linear velocity along the tube. This is fundamental physics. Vector quantities like speed and acceleration add vectorially. Ignoring that fundamental physics is another flaw in this. .. .. Then, the added kinetic energy in the moving fluid is in only direction. It is not increasing the random thermal vibrations. That would require increasing the temperature. This is another flaw in this story. Moving the fluid along the pipe does not raise the temperature. Therefore, the statement at 2:23: "an atom with a higher velocity would have a higher kinetic energy and, therefore, exert a larger force on the pipe walls" is false because it conflates / confuses thermal energy and momentum in one direction. .. .. Consider bouncing a ball on the floor. Each bounce imparts some momentum to the floor. The ball's actual motion is only vertical.. Now, start the room moving (a train car) and the ball still imparts the same momentum to the floor with each bounce. It's actual motion, relative to the stationary ground changes. It has the *SAME* vertical component, but now a horizontal component vectorially added to the vertical motions. The pressure on the floor does not change. . However, these two motions are orthogonal and have no effect on each other. The vertical up[and down bouncing component remains the same. ONLY the ground referenced horizontal component changes as the speed increases. This physics does not change if the ball is bounced on the ground outside the train's window. . This fails on these fundamental physics errors.
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.
So basically there is pressure perpendicular to the wall and pressure parallel to the wall. Obviously pressure parallel to the wall can’t do work on the wall but it can “work” on the fluid itself. In reality, these perpendicular and parallel pressures are just the two contributions to volumetric density of kinetic energy, and because kinetic energy varies with the square of the velocity, you could apply the Pythagoras theorem and say one is simply converting one pressure type to the other pressure type by virtue of the fluid traveling down the narrowing and expanding sections of the pipe. For constant density fluids as we have in this example, you could (ignoring viscosity and in general resistance to fluid flow) additionally say that the sum of perpendicular kinetic energy and parallel kinetic energy is conserved and we are simply converting one type of kinetic energy into the other. Then the gradient of “pressure” down the tube is really just the gradient of the parallel-to-tube contribution to the volumetric kinetic energy density. Ignoring resistance to flow, It does not actually represent a change in the total pressure as the fluid travels down the tube, just a conversion of one subtype of pressure into another. It would be interesting to see how this concept would apply to flow that is “detached” from walls, since in such flow there is not really a “parallel” or “perpendicular” direction to speak of.
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
Thank you! Bernoulli's principle has always been something I had a hard time "accepting", even though I knew it was true. Explaining why something has to be true is *not* the same as explaining why it's true. It's similar to the similarly unsatisfying "conservation of angular momentum" explanation given to explain why a figure skater spins faster when they pull their arms in.
@@EugeneKhutoryansky me too. thank you. you guys are photons of hope and direction in this confusing, wildly vast and over-humbling world of physics textbooks that mostly cause stress and low self-esteem to a student. You impart excellent magnitude of knowledge and show the right direction of thinking. We were scalar. But you help us become vector.
I had so much trouble with wrapping my head around the physics behind Bernoulli but now it all makes sense. It’s so sleek and effective to break things down to the atomic scale and think in terms of inertia. Thank you so much for your brilliant way of teaching.
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.
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Consider the following: a. Utilize electromagnetic radiation energy instead of atoms. b. Utilize a split pipe design so that one side of the pipe carries a charge and the other side of the pipe is insulated. (Possibly different materials on each side of the pipe, one metal, one non-metal). c. Make the pipe in a circular design with the electrical side of the pipe on the outer edges. d. Put this circular device on a space ship so that part of it is shielded, the shield being the movable part that can vary over the electrical part of the pipe. e. By injecting electromagnetic radiation energy of a certain energy frequency into the pipe, would energy be such that it could move a space ship through outer space, (space not being totally empty but also containing 'emr' of various frequencies, 'emr' of course having both an electrical component as well as a magnetic component, as well as any molecules, atoms and sub-atomic particles in outer space, each having their own potential electrical and magnetic components). The interaction of the electrical and/or magnetic forces being the driving force for the space ship. The movable shield controlling the direction of the space ship. f. Hmmmm.................................. Edit: g. The shield also being made out of counter-acting 'emr' so that is is solid state with no moving parts. Just vary which portions are active or not for direction control. h. And a 3 axis ring design to have 360 degree motion ability?
@@saddam8783 I make my 3D animations with the software "Poser." Also, I performed the simulations with an add on (purchased separately) called "Poser Physics." Glad you liked my video.
Can't believe, it is like 3rd time when I have doubt about explanation of some physical phenomena that I found on the internet and then few days later Eugene Khutoryansky uploads video about it. You're brilliant tutor and your videos cover everything that could bother person who wants to understand the subject. Keep up your great work.
look at the orientation of the wings. for air particles to flow above a wing, they would need to have velocity components oriented away from the wing, while flow below the wing would need velocity pointing toward the wing. also Bernoulli's principle isn't solely responsible for the lift force (deflection of the air downward is also important) en.wikipedia.org/wiki/Lift_(force)
@j2ealish That's just a different way of explaining the same thing. A 'vaccuum' is just a way to look at an area with low pressure macroscopically, not on the particle scale, but the two views (macro and micro) coincide perfectly here
@j2ealish I was just addressing what you said in your only comment. There are usually two ways of seeing a physical concept: macro and micro. Another example is chemistry, chemical laws (macro) arise from physical laws (micro)
I'm not sure I came out 100% convinced. It seems convenient to say that the velocity components parallel and perpendicular to the walls change when they enter the narrow region. It is not explained why those would change at the first place? Yes sure, we can say the bombardment with the other molecules is making the changes happen but we then assume that the molecules in the broader region were already slow and caused deflection and slowdown on the incoming new molecules. But why were they slow at the first place?.. Can the principle be explained using a single molecule?.. If not, then why the initial material slowed down needs to be explained.
What happens is the exact same thing in reverse. The components between molecules will still differ. This will cause some of the molecules travel a shorter or a longer distance (depending on the orientation of the momentum) in the same time giving them the opportunity for collision. Obviously this will not be uniform locally but from our perspective we might as well assume that it is.
It's just statistics. An atom moving completely perpendicular will not enter the narrow section until its vector is changed, and one completely horizontal is virtually bound to enter the pipe. It stands to reason, therefore, that the more parallel the motion of the particle, the more likely it will be to enter the pipe. Yes, other atoms can change the vector of motion of each atom, but then that just changes the chance the atom enters the pipe. The atoms can be assumed in their slow stages to have, in average, some parallel speed to the pipe more than if the fluid weren't moving at all, because that's necessary for motion. Brownian motion would dictate some randomness in their motion however fast the atoms were moving.
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.
The difference of small physics and big physics explained. When looking at a fluid as an entity of itself makes it tough to comprehend this law, but when you look at the fluid at the molecular scale, you begin to see that things are actually not that different
Unfortunately, this violates some very common and well understood accepted principles of physics. It repeats the same errors that Charles Crummer makes. .. The statement at 2:07 is correct. "there is no reason to expect an atom with a higher velocity to exert a lower pressure on the walls of the pipe." There can be the same pressure in a fast fluid as a slow fluid. They simply have the same static pressure. Bernoulli is not about speed. It is about changes in speed or velocity which is Acceleration along a path. The pressure on the walls of a sealed jar is the same regardless of the speed of the jar. A fundamental flaw in this misconception at 2:42 is is that there no reason to expect a molecule to have the thermal vibration in only one dimension. These pressure causing vibrations are random in direction and are how they bounce round between other atoms. At any given instant a molecule may be going down and the next at 90 degrees or even 180 degrees to the previous vibration. That simple fact breaks this false logic. .. Then. . . It is the *average* velocity (over time) that has a directed motion when the kinetic energy is added to produce an increase in speed. That directed velocity is vectorially summed to the random vibrations. This is vector addition of velocities. This means that the random vibrations are superimposed onto the linear velocity along the tube. This is fundamental physics. Vector quantities like speed and acceleration add vectorially. Ignoring that fundamental physics is another flaw in this. .. .. Then, the added kinetic energy in the moving fluid is in only direction. It is not increasing the random thermal vibrations. That would require increasing the temperature. This is another flaw in this story. Moving the fluid along the pipe does not raise the temperature. Therefore, the statement at 2:23: "an atom with a higher velocity would have a higher kinetic energy and, therefore, exert a larger force on the pipe walls" is false because it conflates / confuses thermal energy and momentum in one direction. .. .. Consider bouncing a ball on the floor. Each bounce imparts some momentum to the floor. The ball's actual motion is only vertical.. Now, start the room moving (a train car) and the ball still imparts the same momentum to the floor with each bounce. It's actual motion, relative to the stationary ground changes. It has the *SAME* vertical component, but now a horizontal component vectorially added to the vertical motions. The pressure on the floor does not change. . However, these two motions are orthogonal and have no effect on each other. The vertical up[and down bouncing component remains the same. ONLY the ground referenced horizontal component changes as the speed increases. This physics does not change if the ball is bounced on the ground outside the train's window. . This fails on these fundamental physics errors.
all of your videos are very excellent and the classical music in the background is good idea and the animation is very nice and the speaking is very calm and clear
you are a legend for making a topic so hard to imagine this easy to understand that when i got to understand it fully i couldnt control my happiness :)
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.
I love this quick paced, repetitive style of teaching Eugene. It's what I have adopted as my ideal as well. I guess it fits certain minds better; those with fast CPU but small working memory (by analogy). Alas, school lessons were never like this.
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?
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 !
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.
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!!
Unfortunately, this violates some very common and well understood accepted principles of physics. It repeats the same errors that Charles Crummer makes. .. The statement at 2:07 is correct. "there is no reason to expect an atom with a higher velocity to exert a lower pressure on the walls of the pipe." There can be the same pressure in a fast fluid as a slow fluid. They simply have the same static pressure. Bernoulli is not about speed. It is about changes in speed or velocity which is Acceleration along a path. The pressure on the walls of a sealed jar is the same regardless of the speed of the jar. A fundamental flaw in this misconception at 2:42 is is that there no reason to expect a molecule to have the thermal vibration in only one dimension. These pressure causing vibrations are random in direction and are how they bounce round between other atoms. At any given instant a molecule may be going down and the next at 90 degrees or even 180 degrees to the previous vibration. That simple fact breaks this false logic. .. Then. . . It is the *average* velocity (over time) that has a directed motion when the kinetic energy is added to produce an increase in speed. That directed velocity is vectorially summed to the random vibrations. This is vector addition of velocities. This means that the random vibrations are superimposed onto the linear velocity along the tube. This is fundamental physics. Vector quantities like speed and acceleration add vectorially. Ignoring that fundamental physics is another flaw in this. .. .. Then, the added kinetic energy in the moving fluid is in only direction. It is not increasing the random thermal vibrations. That would require increasing the temperature. This is another flaw in this story. Moving the fluid along the pipe does not raise the temperature. Therefore, the statement at 2:23: "an atom with a higher velocity would have a higher kinetic energy and, therefore, exert a larger force on the pipe walls" is false because it conflates / confuses thermal energy and momentum in one direction. .. .. Consider bouncing a ball on the floor. Each bounce imparts some momentum to the floor. The ball's actual motion is only vertical.. Now, start the room moving (a train car) and the ball still imparts the same momentum to the floor with each bounce. It's actual motion, relative to the stationary ground changes. It has the *SAME* vertical component, but now a horizontal component vectorially added to the vertical motions. The pressure on the floor does not change. . However, these two motions are orthogonal and have no effect on each other. The vertical up[and down bouncing component remains the same. ONLY the ground referenced horizontal component changes as the speed increases. This physics does not change if the ball is bounced on the ground outside the train's window. . This fails on these fundamental physics errors.
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.
I had asked this question to I don't know how many friends, professors. When I studied "Obstruction type flow meters" during my engineering, but it remained answered until today. Thank you so much ❤️
Whenever you can reduce a problem to "because particles move at random," I am satisfied. Disorder and statistics is so fundamental to reality. Big fan Eugene!
Thank you for your videos you are my go-to source for understanding a topic thoroughly now. Big ask but could you think about doing a video about why momentum is always conserved? There were some good explanations but with your format, I think it would be better. Keep the amazing videos up!
Thanks. I might go into detail about "why" momentum is conserved in a future video, but I cover the conservation of Momentum and Angular Momentum in my video at ruclips.net/video/PNHSIEO-KOQ/видео.html
I feel proud that I understood this struggling by myself before the video =) What I don't understand is why then blowing the upper side of a paper can make it go up. Bc in that case the higher velocity is due to external force and so the bigger parallel component is not at the expense of lower perpendicular component.
Your explanations are the best! I try to explain scientific subjects to people in the same way, usually biology, and they say that those are the best explanetions they heard about the subjects. We need more videos like yours.
This explanation is excellent for one more reason: suppose the larger outlet pipe is empty at the moment. the small inlet pipe will behave much like a faucet, and spray the liquid directly forward unimpeded, and will not fill the pipe completely until or unless there is some resistance or impedance that causes some of the particles to bounce back. This explanation is fully consistent with how a faucet works, and a similar reasoning applies for how a basin works.
Unfortunately Tony,, this violates some very common and well understood accepted principles of physics. It repeats the same errors that Charles Crummer makes. .. The statement at 2:07 is correct. "there is no reason to expect an atom with a higher velocity to exert a lower pressure on the walls of the pipe." There can be the same pressure in a fast fluid as a slow fluid. They simply have the same static pressure. Bernoulli is not about speed. It is about changes in speed or velocity which is Acceleration along a path. The pressure on the walls of a sealed jar is the same regardless of the speed of the jar. A fundamental flaw in this misconception at 2:42 is is that there no reason to expect a molecule to have the thermal vibration in only one dimension. These pressure causing vibrations are random in direction and are how they bounce round between other atoms. At any given instant a molecule may be going down and the next at 90 degrees or even 180 degrees to the previous vibration. That simple fact breaks this false logic. .. Then. . . It is the *average* velocity (over time) that has a directed motion when the kinetic energy is added to produce an increase in speed. That directed velocity is vectorially summed to the random vibrations. This is vector addition of velocities. This means that the random vibrations are superimposed onto the linear velocity along the tube. This is fundamental physics. Vector quantities like speed and acceleration add vectorially. Ignoring that fundamental physics is another flaw in this. .. .. Then, the added kinetic energy in the moving fluid is in only direction. It is not increasing the random thermal vibrations. That would require increasing the temperature. This is another flaw in this story. Moving the fluid along the pipe does not raise the temperature. Therefore, the statement at 2:23: "an atom with a higher velocity would have a higher kinetic energy and, therefore, exert a larger force on the pipe walls" is false because it conflates / confuses thermal energy and momentum in one direction. .. .. Consider bouncing a ball on the floor. Each bounce imparts some momentum to the floor. The ball's actual motion is only vertical.. Now, start the room moving (a train car) and the ball still imparts the same momentum to the floor with each bounce. It's actual motion, relative to the stationary ground changes. It has the *SAME* vertical component, but now a horizontal component vectorially added to the vertical motions. The pressure on the floor does not change. . However, these two motions are orthogonal and have no effect on each other. The vertical up[and down bouncing component remains the same. ONLY the ground referenced horizontal component changes as the speed increases. This physics does not change if the ball is bounced on the ground outside the train's window. . This fails on these fundamental physics errors.
@@tonysiu8562 Hi Tony, It's Not MY theory. There is an accepted understanding by professionals. So many well meaning amateur scientists, like Eugene here, have it wrong. This is Charles Crummer's misconception that he is repeating, as I explained. Euler figured out that it is a Pressure Gradient that Accelerates fluid while following up on Bernoulli's work in the mid 1700s. I've studied fluid dynamics, read several noted authors and discussed it with some of them. .. This is Newton operating in fluids. A force is what causes a mass to Accelerate and in fluids a Pressure Gradient (difference in pressure between two locations) is what provides the force that Accelerates the fluid's mass. Air and water have mass. and a force causes acceleration. . What I have here should put it into correct perspective for you. *Understanding Bernoulli's Principle Correctly* *kyuoyckftflurrpq.quora.com/*
@@Observ45erAs I understand your view, fluid particles are accelerated in the longitudinal direction (parallel to the axis) by the pressure gradient at the entrance to the narrow section of the Venturi tube, giving them additional longitudinal velocity without affecting their transverse velocity. (On average.) But if the transverse velocity is the same, why do we measure a lower pressure at the wall of the narrow section of the Venturi tube? If the longitudinal velocity is increased without the transverse velocity decreasing then the kinetic energy of the particles has increased. Where did the extra kinetic energy come from?
Can you please make a video on what happens in a supersonic flow (velocity increases with increasing area, as in nozzles), how speed of sound/disturbance is different than the speed of individual molecules. I have always pondered on the fact but never understood it on the molecular level.
*Unfortunately, this speculation is not good science.* The author of this script refuses to accept that a Pressure Gradient causes fluid acceleration as Euler revealed in the mid 1700 while following up on Bernoulli’s work. Air has mass and a force is required to accelerate any mass, even fluids. Pressure is the source of that force. Newton for fluids. And, BTW, Euler derived what we now call Bernoulli's Equation. There is no indication that Bernoulli understood the cause-and-effect for what he saw in that typical venturi tube as the pressure/velocity inverse relationship. This video’s explanation is very weak in its cause and effect logic. In fact, I am unable to follow the logic. Most times I’ve seen people trying to explain pressures down to the molecule level; they go astray in their assumptions as though it is simple balls - as a Newton’s “Hail of bullets”. This video’s logic is faulty as follows. It appears to be using another common misconception. Namely, that the random thermal motion of the molecules is changed by a net speed of the fluid in one direction. This claim is that the velocity and therefore momentum toward the wall is reduced by adding a velocity along the wall. This is clearly nonsense. The temperature random motion is superimposed on the overall bulk velocity in any direction. There is nothing to suggest that molecules change their random vibration to more in one direction (along a pipe) and less in another (perpendicular to the wall). They vibrate the same thermal way regardless of a net movement in one direction and the component of that motion toward a wall is unchanged by that directed speed. This is how vector addition of velocities works. Orthogonal velocities do not affect each other. This is just like the classical physics example of a cannon-ball that has its horizontal speed unaffected by gravity and its vertical acceleration by gravity unaffected by the horizontal speed. By this reasoning, air in a sealed jar that is shot from a cannon has altered vibration motions from when sitting still. This cannot be true. For example, here is how velocities like this will add: A molecule moving thermally at some instant with a velocity at 45 degrees (up right) with speed (magnitude) 1.0 has an upward component toward a wall above it of 0.707 and a forward component to the right of 0.707. Adding a horizontal speed to the right of 5.0 results in a new horizontal speed component of 5.707 and the same vertical component of 0.707. Velocities add vectorially. The component of momentum perpendicular to the wall is unchanged. The air exiting any blower into open air is at the very same pressure as the still air around it. This can easily be measured by anyone, just as it is by professional aerodynamicists every day as shown here in Weltner, Fig 3: user.uni-frankfurt.de/~weltner/Misinterpretations%20of%20Bernoullis%20Law%202011%20internet.pdf Finally, the video completely ignores the presence of the well-known boundary layer which is completely motionless at the surface, so as a result, this claim of the molecules moving along the tube is completely invalid before even entering this above discussion. *This is bad science.*
Unfortunately, this violates some very common and well understood accepted principles of physics. It repeats the same errors that Charles Crummer makes. .. The statement at 2:07 is correct. "there is no reason to expect an atom with a higher velocity to exert a lower pressure on the walls of the pipe." There can be the same pressure in a fast fluid as a slow fluid. They simply have the same static pressure. Bernoulli is not about speed. It is about changes in speed or velocity which is Acceleration along a path. The pressure on the walls of a sealed jar is the same regardless of the speed of the jar. A fundamental flaw in this misconception at 2:42 is is that there no reason to expect a molecule to have the thermal vibration in only one dimension. These pressure causing vibrations are random in direction and are how they bounce round between other atoms. At any given instant a molecule may be going down and the next at 90 degrees or even 180 degrees to the previous vibration. That simple fact breaks this false logic. .. Then. . . It is the *average* velocity (over time) that has a directed motion when the kinetic energy is added to produce an increase in speed. That directed velocity is vectorially summed to the random vibrations. This is vector addition of velocities. This means that the random vibrations are superimposed onto the linear velocity along the tube. This is fundamental physics. Vector quantities like speed and acceleration add vectorially. Ignoring that fundamental physics is another flaw in this. .. .. Then, the added kinetic energy in the moving fluid is in only direction. It is not increasing the random thermal vibrations. That would require increasing the temperature. This is another flaw in this story. Moving the fluid along the pipe does not raise the temperature. Therefore, the statement at 2:23: "an atom with a higher velocity would have a higher kinetic energy and, therefore, exert a larger force on the pipe walls" is false because it conflates / confuses thermal energy and momentum in one direction. .. .. Consider bouncing a ball on the floor. Each bounce imparts some momentum to the floor. The ball's actual motion is only vertical.. Now, start the room moving (a train car) and the ball still imparts the same momentum to the floor with each bounce. It's actual motion, relative to the stationary ground changes. It has the *SAME* vertical component, but now a horizontal component vectorially added to the vertical motions. The pressure on the floor does not change. . However, these two motions are orthogonal and have no effect on each other. The vertical up[and down bouncing component remains the same. ONLY the ground referenced horizontal component changes as the speed increases. This physics does not change if the ball is bounced on the ground outside the train's window. . This fails on these fundamental physics errors.
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When I meet God,
I am going to ask him two questions:
Why relativity ? And
why turbulence ?
I really believe he will have an answer for the first.
Werner Heisenberg
Muchas gracias!
how antenna works
I want to thank you for this explanation. This has been bothering me for 50 years and I have a BS chemical engineering and I study physics as a hobby. This is the first time this phenomenon has ever made physical sense to me.
Eugene, your explanation of why the pressure goes down in the narrow part of the pipe is not correct.
The pressure in the wide part of the pipe that followes after the narrow part is still lower than the pressure in the narrow part of the pipe.
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.
@@EugeneKhutoryansky 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.
@@EugeneKhutoryansky 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.
As Feynman said, knowing all the bird names of the world does not tell you anything about what birds are.
jmchez That’s why I skipped learning their names.
@@jmchez atomic theory + first principles thinking 💪😎
ur mum
Its the proccess. Step 1. Knowing and step 2. Understanding it... So step 3?
Me: "Ok. Sleepy time"
RUclips algorithm : "Not until you truly understand the Bernoulli principle in earnest!"
Me: haha, I already know how this works.
Me: well, I learned something new today!
pozitivity
Understanding how this works is far superior to just remembering. Thanks 🙏
Thanks.
When I intuitively understand it, then I remember it. Thanks
@@douginorlando6260 Exactly right. If you understand something, you can remember it. If you don't, it's very difficult and often impossible. 🙂
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.
@@EugeneKhutoryansky 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.
@@EugeneKhutoryansky wau that makes sense. Thank you :)
@pyropulse Yes you are right, the analysis should be in molecular level not atomic.
The legacy that this teacher is leaving to the world is incalculably big
Thanks for the compliment.
Unfortunately, this violates some very common and well understood accepted principles of physics. Charles Crummer makes the same errors, which doesn't make it correct.
..
The statement at 2:07 is correct. "there is no reason to expect an atom with a higher velocity to exert a lower pressure on the walls of the pipe."
There can be the same pressure in a fast fluid as a slow fluid. They simply have the same static pressure. Bernoulli is not about speed. It is about changes in speed or velocity which is Acceleration along a path.
The pressure on the walls of a sealed jar is the same regardless of the speed of the jar.
A fundamental flaw in this misconception at 2:42 is is that there no reason to expect a molecule to have the thermal vibration in only one dimension. These pressure causing vibrations are random in direction and are how they bounce round between other atoms.
At any given instant a molecule may be going down and the next at 90 degrees or even 180 degrees to the previous vibration.
That simple fact breaks this false logic.
..
Then. . .
It is the average velocity (over time) that has a directed motion when the kinetic energy is added to produce an increase in speed. That directed velocity is vectorially summed to the random vibrations. This is vector addition of velocities. This means that the random vibrations are superimposed onto the linear velocity along the tube. This is fundamental physics. Vector quantities like speed and acceleration add vectorially.
Ignoring that fundamental physics is another flaw in this.
..
..
Then, the added kinetic energy in the moving fluid is in only direction. It is not increasing the random thermal vibrations. That would require increasing the temperature. This is another flaw in this story. Moving the fluid along the pipe does not raise the temperature.
Therefore, the statement at 2:23: "an atom with a higher velocity would have a higher kinetic energy and, therefore, exert a larger force on the pipe walls" is false because it conflates / confuses thermal energy and momentum in one direction.
..
..
Consider bouncing a ball on the floor. Each bounce imparts some momentum to the floor. The ball's actual motion is only vertical..
Now, start the room moving (a train car) and the ball still imparts the same momentum to the floor with each bounce. It's actual motion, relative to the stationary ground changes. It has the SAME vertical component, but now a horizontal component vectorially added to the vertical motions. The pressure on the floor does not change.
.
However, these two motions are orthogonal and have no effect on each other. The vertical up[and down bouncing component remains the same. ONLY the ground referenced horizontal component changes as the speed increases.
This physics does not change if the ball is bounced on the ground outside the train's window.
.
This fails on these fundamental physics errors.
@@Observ45ernothing you’ve said here explains Bernoulli’s. Furthermore, nothing said here entirely disagrees with the video’s point. Lets think about a couple of points.
1) pumping fluid through a pipe absolutely does increase the temperature. This increase in temperature primarily occurs at the impeller of the pump, but eventually, all the fluids kinetic energy is dissipated when it stops flowing, as heat. There is friction and this linear motion is eventually all converted into vibration/temperature increase. Therefore this net net movement of the entire fluid body absolutely does count as part of the motion that sums to temperature. It may not be much from the perspective of the fluid at the time until the fluid’s motion is dissipated because the molecules aren’t necessarily moving faster relative to one another. But any probe or obstructing fluid in the flow stream will experience more collisions on the flow-ward side and thus an increase in temperature. This is what limits supersonic aircraft - the temperature of the skin gets so high from the increased collisions at the leading edge. There is also an increase in pressure at the flow-ward surface for the same reason - and as we know in fluids especially gasses temperature and pressure are so closely tied. In fluids this low pressure at the vena contracta can be below equilibrium vapor pressure and cause vapor bubbles.
2) it isn’t like the pressure in a venturi drops to zero. There ARE still random molecule collisions with the pipe wall at the low pressure surface, but they do occur less frequently thus the low pressure. There is also a temperature drop at the low pressure point in gas, and in liquids if they are flashing especially. Look at a metering valve in refrigeration for example.
The video is correct and you are incorrect to completely separate molecular motion associated with temperature from molecular motion associated with pressure and net fluid motion as well.
Finally understood this concept...very intuitive explanation which is rather hard to find in any textbook..
Thanks.
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
@@pranalingle9424 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 RUclipsr 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.
I would love to see a video on the counterintuitive nature of supersonic flows in a converging/diverging nozzle. I think this style of visualization would serve it well, showing how the gas slows down as the nozzle converges and speeds up while it diverges.
This is magnificent ! After fifty years of unsatisfactory explanations finally an explanation that makes sense ! My professors would bombard me with formulas and differential equations but never bothered to explain what was really happening. I’m eternally grateful to you ! 🙋♀️👍🙏🏻
Thanks. I am glad you liked my explanation. Yes, what you described is a symbol of what is wrong with technical education. Everything is "explained" with equations. In other words, it isn't explained at all.
Unfortunately, Claire, this violates some very common and well understood accepted principles of physics. It repeats the same errors that Charles Crummer makes.
..
The statement at 2:07 is correct. "there is no reason to expect an atom with a higher velocity to exert a lower pressure on the walls of the pipe."
There can be the same pressure in a fast fluid as a slow fluid. They simply have the same static pressure. Bernoulli is not about speed. It is about changes in speed or velocity which is Acceleration along a path.
The pressure on the walls of a sealed jar is the same regardless of the speed of the jar.
A fundamental flaw in this misconception at 2:42 is is that there no reason to expect a molecule to have the thermal vibration in only one dimension. These pressure causing vibrations are random in direction and are how they bounce round between other atoms.
At any given instant a molecule may be going down and the next at 90 degrees or even 180 degrees to the previous vibration.
That simple fact breaks this false logic.
..
Then. . .
It is the *average* velocity (over time) that has a directed motion when the kinetic energy is added to produce an increase in speed. That directed velocity is vectorially summed to the random vibrations. This is vector addition of velocities. This means that the random vibrations are superimposed onto the linear velocity along the tube. This is fundamental physics. Vector quantities like speed and acceleration add vectorially.
Ignoring that fundamental physics is another flaw in this.
..
..
Then, the added kinetic energy in the moving fluid is in only direction. It is not increasing the random thermal vibrations. That would require increasing the temperature. This is another flaw in this story. Moving the fluid along the pipe does not raise the temperature.
Therefore, the statement at 2:23: "an atom with a higher velocity would have a higher kinetic energy and, therefore, exert a larger force on the pipe walls" is false because it conflates / confuses thermal energy and momentum in one direction.
..
..
Consider bouncing a ball on the floor. Each bounce imparts some momentum to the floor. The ball's actual motion is only vertical..
Now, start the room moving (a train car) and the ball still imparts the same momentum to the floor with each bounce. It's actual motion, relative to the stationary ground changes. It has the *SAME* vertical component, but now a horizontal component vectorially added to the vertical motions. The pressure on the floor does not change.
.
However, these two motions are orthogonal and have no effect on each other. The vertical up[and down bouncing component remains the same. ONLY the ground referenced horizontal component changes as the speed increases.
This physics does not change if the ball is bounced on the ground outside the train's window.
.
This fails on these fundamental physics errors.
This is the best video explaining the intuitions of Bernoulli’s principle! I’m going to share this with my friends in my engineering classes! Thank you!
I am glad you liked my video. 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
"the highly unsatisfying explanation typically given" damn throwing some serious shade lol
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.
This channel is a piece of art
Thanks for the compliment.
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.
🌟Concept is now crystal clear in my head. Thank u so much👍
Thanks.
Unfortunately, this violates some very common and well understood accepted principles of physics. It repeats the same errors that Charles Crummer makes.
..
The statement at 2:07 is correct. "there is no reason to expect an atom with a higher velocity to exert a lower pressure on the walls of the pipe."
There can be the same pressure in a fast fluid as a slow fluid. They simply have the same static pressure. Bernoulli is not about speed. It is about changes in speed or velocity which is Acceleration along a path.
The pressure on the walls of a sealed jar is the same regardless of the speed of the jar.
A fundamental flaw in this misconception at 2:42 is is that there no reason to expect a molecule to have the thermal vibration in only one dimension. These pressure causing vibrations are random in direction and are how they bounce round between other atoms.
At any given instant a molecule may be going down and the next at 90 degrees or even 180 degrees to the previous vibration.
That simple fact breaks this false logic.
..
Then. . .
It is the *average* velocity (over time) that has a directed motion when the kinetic energy is added to produce an increase in speed. That directed velocity is vectorially summed to the random vibrations. This is vector addition of velocities. This means that the random vibrations are superimposed onto the linear velocity along the tube. This is fundamental physics. Vector quantities like speed and acceleration add vectorially.
Ignoring that fundamental physics is another flaw in this.
..
..
Then, the added kinetic energy in the moving fluid is in only direction. It is not increasing the random thermal vibrations. That would require increasing the temperature. This is another flaw in this story. Moving the fluid along the pipe does not raise the temperature.
Therefore, the statement at 2:23: "an atom with a higher velocity would have a higher kinetic energy and, therefore, exert a larger force on the pipe walls" is false because it conflates / confuses thermal energy and momentum in one direction.
..
..
Consider bouncing a ball on the floor. Each bounce imparts some momentum to the floor. The ball's actual motion is only vertical..
Now, start the room moving (a train car) and the ball still imparts the same momentum to the floor with each bounce. It's actual motion, relative to the stationary ground changes. It has the *SAME* vertical component, but now a horizontal component vectorially added to the vertical motions. The pressure on the floor does not change.
.
However, these two motions are orthogonal and have no effect on each other. The vertical up[and down bouncing component remains the same. ONLY the ground referenced horizontal component changes as the speed increases.
This physics does not change if the ball is bounced on the ground outside the train's window.
.
This fails on these fundamental physics errors.
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.
So basically there is pressure perpendicular to the wall and pressure parallel to the wall. Obviously pressure parallel to the wall can’t do work on the wall but it can “work” on the fluid itself.
In reality, these perpendicular and parallel pressures are just the two contributions to volumetric density of kinetic energy, and because kinetic energy varies with the square of the velocity, you could apply the Pythagoras theorem and say one is simply converting one pressure type to the other pressure type by virtue of the fluid traveling down the narrowing and expanding sections of the pipe. For constant density fluids as we have in this example, you could (ignoring viscosity and in general resistance to fluid flow) additionally say that the sum of perpendicular kinetic energy and parallel kinetic energy is conserved and we are simply converting one type of kinetic energy into the other. Then the gradient of “pressure” down the tube is really just the gradient of the parallel-to-tube contribution to the volumetric kinetic energy density. Ignoring resistance to flow, It does not actually represent a change in the total pressure as the fluid travels down the tube, just a conversion of one subtype of pressure into another.
It would be interesting to see how this concept would apply to flow that is “detached” from walls, since in such flow there is not really a “parallel” or “perpendicular” direction to speak of.
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.
3:53, that eureka moment. A moment that has happened many times for me thanks to this channel's videos.
Glad to hear that. Thanks.
Legend’s back
Thank you! Bernoulli's principle has always been something I had a hard time "accepting", even though I knew it was true. Explaining why something has to be true is *not* the same as explaining why it's true. It's similar to the similarly unsatisfying "conservation of angular momentum" explanation given to explain why a figure skater spins faster when they pull their arms in.
Thanks. I am glad you liked my explanation.
*You makes us happy with those beautiful videos. may you remain happy all life*
Thanks. I am glad my videos make you happy.
@@EugeneKhutoryansky
Yes😊😊😊😊
@@EugeneKhutoryansky me too. thank you. you guys are photons of hope and direction in this confusing, wildly vast and over-humbling world of physics textbooks that mostly cause stress and low self-esteem to a student.
You impart excellent magnitude of knowledge and show the right direction of thinking.
We were scalar. But you help us become vector.
I had so much trouble with wrapping my head around the physics behind Bernoulli but now it all makes sense. It’s so sleek and effective to break things down to the atomic scale and think in terms of inertia. Thank you so much for your brilliant way of teaching.
Thanks.
I am studying for the MCAT, this was making me crazy, now I can breathe again.
Thanks, this explanation is highly satisfying.
I am glad you liked my explanation.
such a counterintuitive idea but it all makes sense now! Great explanation with some great music!
Thanks. Glad you liked my explanation.
I once searched this exact topic for days without finding anything satisfying enough... Thank you.
Glad this video is what you were looking for.
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.
Apart from the repetition, I enjoyed the video a lot. Apart from the repetition, I enjoyed the video a lot.
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Thanks.
Consider the following:
a. Utilize electromagnetic radiation energy instead of atoms.
b. Utilize a split pipe design so that one side of the pipe carries a charge and the other side of the pipe is insulated. (Possibly different materials on each side of the pipe, one metal, one non-metal).
c. Make the pipe in a circular design with the electrical side of the pipe on the outer edges.
d. Put this circular device on a space ship so that part of it is shielded, the shield being the movable part that can vary over the electrical part of the pipe.
e. By injecting electromagnetic radiation energy of a certain energy frequency into the pipe, would energy be such that it could move a space ship through outer space, (space not being totally empty but also containing 'emr' of various frequencies, 'emr' of course having both an electrical component as well as a magnetic component, as well as any molecules, atoms and sub-atomic particles in outer space, each having their own potential electrical and magnetic components). The interaction of the electrical and/or magnetic forces being the driving force for the space ship. The movable shield controlling the direction of the space ship.
f. Hmmmm..................................
Edit: g. The shield also being made out of counter-acting 'emr' so that is is solid state with no moving parts. Just vary which portions are active or not for direction control.
h. And a 3 axis ring design to have 360 degree motion ability?
Can you share your alma mater
Could you tell us which software is used to make this awesome video?😍😍🙂🙂😍😍
@@saddam8783 I make my 3D animations with the software "Poser." Also, I performed the simulations with an add on (purchased separately) called "Poser Physics." Glad you liked my video.
Obrigado pelas legendas em português do Brasil. Abraços!
Can't believe, it is like 3rd time when I have doubt about explanation of some physical phenomena that I found on the internet and then few days later Eugene Khutoryansky uploads video about it. You're brilliant tutor and your videos cover everything that could bother person who wants to understand the subject. Keep up your great work.
Thanks for the compliment.
What about on the wing of an aircraft? This doesn’t seem to apply..
look at the orientation of the wings. for air particles to flow above a wing, they would need to have velocity components oriented away from the wing, while flow below the wing would need velocity pointing toward the wing. also Bernoulli's principle isn't solely responsible for the lift force (deflection of the air downward is also important) en.wikipedia.org/wiki/Lift_(force)
@j2ealish Very likely!
@j2ealish That's just a different way of explaining the same thing. A 'vaccuum' is just a way to look at an area with low pressure macroscopically, not on the particle scale, but the two views (macro and micro) coincide perfectly here
@j2ealish I was just addressing what you said in your only comment. There are usually two ways of seeing a physical concept: macro and micro. Another example is chemistry, chemical laws (macro) arise from physical laws (micro)
I'd love if Prof. Kuthoryansky would debunk the classical "why aircraft fly" theory as well. I feel that this is usually also not explained correctly.
EUGENE YOU ARE A BLESSED MAN
Thanks.
JACQUI YOU ARE BLESSED MAN
@@yuzumaxwell OH MY GOD ! ! ! ! ! ! !
I'm not sure I came out 100% convinced.
It seems convenient to say that the velocity components parallel and perpendicular to the walls change when they enter the narrow region. It is not explained why those would change at the first place? Yes sure, we can say the bombardment with the other molecules is making the changes happen but we then assume that the molecules in the broader region were already slow and caused deflection and slowdown on the incoming new molecules. But why were they slow at the first place?..
Can the principle be explained using a single molecule?.. If not, then why the initial material slowed down needs to be explained.
What happens is the exact same thing in reverse. The components between molecules will still differ. This will cause some of the molecules travel a shorter or a longer distance (depending on the orientation of the momentum) in the same time giving them the opportunity for collision. Obviously this will not be uniform locally but from our perspective we might as well assume that it is.
It's just statistics. An atom moving completely perpendicular will not enter the narrow section until its vector is changed, and one completely horizontal is virtually bound to enter the pipe. It stands to reason, therefore, that the more parallel the motion of the particle, the more likely it will be to enter the pipe. Yes, other atoms can change the vector of motion of each atom, but then that just changes the chance the atom enters the pipe. The atoms can be assumed in their slow stages to have, in average, some parallel speed to the pipe more than if the fluid weren't moving at all, because that's necessary for motion. Brownian motion would dictate some randomness in their motion however fast the atoms were moving.
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.
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.
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.
Excellent as always. I never stopped to ponder this, your explanation makes all kind of Noetherian sense.
Thanks for the compliment and I am glad you liked my explanation.
The difference of small physics and big physics explained. When looking at a fluid as an entity of itself makes it tough to comprehend this law, but when you look at the fluid at the molecular scale, you begin to see that things are actually not that different
Unfortunately, this violates some very common and well understood accepted principles of physics. It repeats the same errors that Charles Crummer makes.
..
The statement at 2:07 is correct. "there is no reason to expect an atom with a higher velocity to exert a lower pressure on the walls of the pipe."
There can be the same pressure in a fast fluid as a slow fluid. They simply have the same static pressure. Bernoulli is not about speed. It is about changes in speed or velocity which is Acceleration along a path.
The pressure on the walls of a sealed jar is the same regardless of the speed of the jar.
A fundamental flaw in this misconception at 2:42 is is that there no reason to expect a molecule to have the thermal vibration in only one dimension. These pressure causing vibrations are random in direction and are how they bounce round between other atoms.
At any given instant a molecule may be going down and the next at 90 degrees or even 180 degrees to the previous vibration.
That simple fact breaks this false logic.
..
Then. . .
It is the *average* velocity (over time) that has a directed motion when the kinetic energy is added to produce an increase in speed. That directed velocity is vectorially summed to the random vibrations. This is vector addition of velocities. This means that the random vibrations are superimposed onto the linear velocity along the tube. This is fundamental physics. Vector quantities like speed and acceleration add vectorially.
Ignoring that fundamental physics is another flaw in this.
..
..
Then, the added kinetic energy in the moving fluid is in only direction. It is not increasing the random thermal vibrations. That would require increasing the temperature. This is another flaw in this story. Moving the fluid along the pipe does not raise the temperature.
Therefore, the statement at 2:23: "an atom with a higher velocity would have a higher kinetic energy and, therefore, exert a larger force on the pipe walls" is false because it conflates / confuses thermal energy and momentum in one direction.
..
..
Consider bouncing a ball on the floor. Each bounce imparts some momentum to the floor. The ball's actual motion is only vertical..
Now, start the room moving (a train car) and the ball still imparts the same momentum to the floor with each bounce. It's actual motion, relative to the stationary ground changes. It has the *SAME* vertical component, but now a horizontal component vectorially added to the vertical motions. The pressure on the floor does not change.
.
However, these two motions are orthogonal and have no effect on each other. The vertical up[and down bouncing component remains the same. ONLY the ground referenced horizontal component changes as the speed increases.
This physics does not change if the ball is bounced on the ground outside the train's window.
.
This fails on these fundamental physics errors.
all of your videos are very excellent and the classical music in the background is good idea and the animation is very nice and the speaking is very calm and clear
Thanks.
This video is so mind-blowing!!
I hope you make this kind of video often 🤣
you are a legend for making a topic so hard to imagine this easy to understand that when i got to understand it fully i couldnt control my happiness :)
I am glad you enjoyed my video. Thanks for the compliments.
Wow! i never thought of it in this way... Thanks...Also amazing that you respond to most of the comments
Thank. I am glad you liked my explanation.
Opened my mindin therms of venturi effect and fluid dynamics in engines.
Thank you so much!
Thanks. Glad you enjoyed my video.
ThankU for sharing and posting.
Thanks.
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.
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.
I really enjoy your work.
Thank you ;
Eugene Khutoryansky
Kira Vincent.
Thank you. I am glad you enjoy the videos.
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 love this quick paced, repetitive style of teaching Eugene. It's what I have adopted as my ideal as well. I guess it fits certain minds better; those with fast CPU but small working memory (by analogy). Alas, school lessons were never like this.
Glad you liked my video. Thanks.
I really appreciate the quallity of these videos.
Thanks.
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.
Very nice video. Thank you
Thanks. I am glad you liked my video.
Thanks! Haven't clicked on a video as fast as this in a long time.
So simple, so satusfying, so beautyfull... Love it!
Thanks for the compliment. Glad you liked it.
The videos you make give us the most intuitive explanations. Thanks a lot for this useful content. Please keep em coming :)
Thanks for the compliment. More videos are on their way.
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.
I've been searching for way too long for somebody who can actually explain Bernoulli's principle. Thanks!
Glad my video was helpful.
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.
Thank you. It's been haunting me for years.
Thanks.
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.
OMGGGG THE ONLY REAL EXPLENATION OF THIS PRINCIPLE FINALLLY THANK YOUU!!!!!!!
Thanks.
You just solved a problem that I couldn't understand with all the books and professors of my engineering classes. Thank you! 😊
Glad you enjoyed my video. Thanks.
This channel is an answer to prayer
Thanks for the compliment.
Unfortunately, this violates some very common and well understood accepted principles of physics. It repeats the same errors that Charles Crummer makes.
..
The statement at 2:07 is correct. "there is no reason to expect an atom with a higher velocity to exert a lower pressure on the walls of the pipe."
There can be the same pressure in a fast fluid as a slow fluid. They simply have the same static pressure. Bernoulli is not about speed. It is about changes in speed or velocity which is Acceleration along a path.
The pressure on the walls of a sealed jar is the same regardless of the speed of the jar.
A fundamental flaw in this misconception at 2:42 is is that there no reason to expect a molecule to have the thermal vibration in only one dimension. These pressure causing vibrations are random in direction and are how they bounce round between other atoms.
At any given instant a molecule may be going down and the next at 90 degrees or even 180 degrees to the previous vibration.
That simple fact breaks this false logic.
..
Then. . .
It is the *average* velocity (over time) that has a directed motion when the kinetic energy is added to produce an increase in speed. That directed velocity is vectorially summed to the random vibrations. This is vector addition of velocities. This means that the random vibrations are superimposed onto the linear velocity along the tube. This is fundamental physics. Vector quantities like speed and acceleration add vectorially.
Ignoring that fundamental physics is another flaw in this.
..
..
Then, the added kinetic energy in the moving fluid is in only direction. It is not increasing the random thermal vibrations. That would require increasing the temperature. This is another flaw in this story. Moving the fluid along the pipe does not raise the temperature.
Therefore, the statement at 2:23: "an atom with a higher velocity would have a higher kinetic energy and, therefore, exert a larger force on the pipe walls" is false because it conflates / confuses thermal energy and momentum in one direction.
..
..
Consider bouncing a ball on the floor. Each bounce imparts some momentum to the floor. The ball's actual motion is only vertical..
Now, start the room moving (a train car) and the ball still imparts the same momentum to the floor with each bounce. It's actual motion, relative to the stationary ground changes. It has the *SAME* vertical component, but now a horizontal component vectorially added to the vertical motions. The pressure on the floor does not change.
.
However, these two motions are orthogonal and have no effect on each other. The vertical up[and down bouncing component remains the same. ONLY the ground referenced horizontal component changes as the speed increases.
This physics does not change if the ball is bounced on the ground outside the train's window.
.
This fails on these fundamental physics errors.
Great Channel
Thanks for making such channel !
Thanks. I am glad you like my videos.
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.
Finally I get this phenomena! Thank you!
Thanks.
I had asked this question to I don't know how many friends, professors. When I studied "Obstruction type flow meters" during my engineering, but it remained answered until today. Thank you so much ❤️
Glad my video was helpful. Thanks.
@@EugeneKhutoryansky ❤️❤️❤️
At last, after 45 years of searching for an understandable explanation, I understand. Thank you, Eugene.
Thanks.
Whenever you can reduce a problem to "because particles move at random," I am satisfied. Disorder and statistics is so fundamental to reality. Big fan Eugene!
Glad you liked my videos. Thanks.
Thank you Eugene Sir. Learning Physics at lockdown gives another kick in life
Best Bernoulli principal video I’ve ever seen, thanks!
Thanks. I am glad you liked my video.
Thank you for your videos you are my go-to source for understanding a topic thoroughly now. Big ask but could you think about doing a video about why momentum is always conserved? There were some good explanations but with your format, I think it would be better. Keep the amazing videos up!
Thanks. I might go into detail about "why" momentum is conserved in a future video, but I cover the conservation of Momentum and Angular Momentum in my video at ruclips.net/video/PNHSIEO-KOQ/видео.html
I feel proud that I understood this struggling by myself before the video =)
What I don't understand is why then blowing the upper side of a paper can make it go up. Bc in that case the higher velocity is due to external force and so the bigger parallel component is not at the expense of lower perpendicular component.
Your explanations are the best!
I try to explain scientific subjects to people in the same way, usually biology, and they say that those are the best explanetions they heard about the subjects.
We need more videos like yours.
Thanks for the compliments about my explanations.
oh my God thank you soooooo much!!!! the video was reallly eligant
Thanks. I am glad you liked my video.
Hats off to you! You just cleared a thing which is draining my energy from a long time. Thank You!!
Glad my video was helpful. Thanks.
This explanation is excellent for one more reason: suppose the larger outlet pipe is empty at the moment. the small inlet pipe will behave much like a faucet, and spray the liquid directly forward unimpeded, and will not fill the pipe completely until or unless there is some resistance or impedance that causes some of the particles to bounce back. This explanation is fully consistent with how a faucet works, and a similar reasoning applies for how a basin works.
Beautifully explained, very intuitive.
Thanks for the compliment. I am glad you liked my explanation.
I can't stop myself from watching more...awesome content with interactive animation.
Thanks. Glad you like my videos.
Best explanation of Bernoulli s principle of all time!
Thanks for the compliment about my explanation.
Unfortunately Tony,, this violates some very common and well understood accepted principles of physics. It repeats the same errors that Charles Crummer makes.
..
The statement at 2:07 is correct. "there is no reason to expect an atom with a higher velocity to exert a lower pressure on the walls of the pipe."
There can be the same pressure in a fast fluid as a slow fluid. They simply have the same static pressure. Bernoulli is not about speed. It is about changes in speed or velocity which is Acceleration along a path.
The pressure on the walls of a sealed jar is the same regardless of the speed of the jar.
A fundamental flaw in this misconception at 2:42 is is that there no reason to expect a molecule to have the thermal vibration in only one dimension. These pressure causing vibrations are random in direction and are how they bounce round between other atoms.
At any given instant a molecule may be going down and the next at 90 degrees or even 180 degrees to the previous vibration.
That simple fact breaks this false logic.
..
Then. . .
It is the *average* velocity (over time) that has a directed motion when the kinetic energy is added to produce an increase in speed. That directed velocity is vectorially summed to the random vibrations. This is vector addition of velocities. This means that the random vibrations are superimposed onto the linear velocity along the tube. This is fundamental physics. Vector quantities like speed and acceleration add vectorially.
Ignoring that fundamental physics is another flaw in this.
..
..
Then, the added kinetic energy in the moving fluid is in only direction. It is not increasing the random thermal vibrations. That would require increasing the temperature. This is another flaw in this story. Moving the fluid along the pipe does not raise the temperature.
Therefore, the statement at 2:23: "an atom with a higher velocity would have a higher kinetic energy and, therefore, exert a larger force on the pipe walls" is false because it conflates / confuses thermal energy and momentum in one direction.
..
..
Consider bouncing a ball on the floor. Each bounce imparts some momentum to the floor. The ball's actual motion is only vertical..
Now, start the room moving (a train car) and the ball still imparts the same momentum to the floor with each bounce. It's actual motion, relative to the stationary ground changes. It has the *SAME* vertical component, but now a horizontal component vectorially added to the vertical motions. The pressure on the floor does not change.
.
However, these two motions are orthogonal and have no effect on each other. The vertical up[and down bouncing component remains the same. ONLY the ground referenced horizontal component changes as the speed increases.
This physics does not change if the ball is bounced on the ground outside the train's window.
.
This fails on these fundamental physics errors.
@@Observ45er this deserve another video to explain your theory
@@tonysiu8562 Hi Tony, It's Not MY theory. There is an accepted understanding by professionals. So many well meaning amateur scientists, like Eugene here, have it wrong. This is Charles Crummer's misconception that he is repeating, as I explained.
Euler figured out that it is a Pressure Gradient that Accelerates fluid while following up on Bernoulli's work in the mid 1700s. I've studied fluid dynamics, read several noted authors and discussed it with some of them.
..
This is Newton operating in fluids. A force is what causes a mass to Accelerate and in fluids a Pressure Gradient (difference in pressure between two locations) is what provides the force that Accelerates the fluid's mass. Air and water have mass. and a force causes acceleration.
.
What I have here should put it into correct perspective for you.
*Understanding Bernoulli's Principle Correctly*
*kyuoyckftflurrpq.quora.com/*
@@Observ45erAs I understand your view, fluid particles are accelerated in the longitudinal direction (parallel to the axis) by the pressure gradient at the entrance to the narrow section of the Venturi tube, giving them additional longitudinal velocity without affecting their transverse velocity. (On average.) But if the transverse velocity is the same, why do we measure a lower pressure at the wall of the narrow section of the Venturi tube? If the longitudinal velocity is increased without the transverse velocity decreasing then the kinetic energy of the particles has increased. Where did the extra kinetic energy come from?
Wow, I have used this principle at work for years, but only now do I understand how it works! Thank you so very much!!
Glad you liked my video. Thanks.
Again, creating outstanding, easy to understand videos, thank you
Thanks.
OMG! This video is a masterpiece! I always questioned that, but never really get a good explanation for it.
Glad you liked my video. Thanks for the compliment.
Thrilled seeing more frequents-uploads , even though finals are upon us. Regards :)
Can you please make a video on what happens in a supersonic flow (velocity increases with increasing area, as in nozzles), how speed of sound/disturbance is different than the speed of individual molecules. I have always pondered on the fact but never understood it on the molecular level.
I will add that to my list of topics for future videos. Thanks.
You guys are really doing something great!
Thanks for the compliment.
*Unfortunately, this speculation is not good science.*
The author of this script refuses to accept that a Pressure Gradient causes fluid acceleration as Euler revealed in the mid 1700 while following up on Bernoulli’s work. Air has mass and a force is required to accelerate any mass, even fluids. Pressure is the source of that force.
Newton for fluids.
And, BTW, Euler derived what we now call Bernoulli's Equation. There is no indication that Bernoulli understood the cause-and-effect for what he saw in that typical venturi tube as the pressure/velocity inverse relationship.
This video’s explanation is very weak in its cause and effect logic. In fact, I am unable to follow the logic. Most times I’ve seen people trying to explain pressures down to the molecule level; they go astray in their assumptions as though it is simple balls - as a Newton’s “Hail of bullets”.
This video’s logic is faulty as follows.
It appears to be using another common misconception. Namely, that the random thermal motion of the molecules is changed by a net speed of the fluid in one direction. This claim is that the velocity and therefore momentum toward the wall is reduced by adding a velocity along the wall. This is clearly nonsense. The temperature random motion is superimposed on the overall bulk velocity in any direction.
There is nothing to suggest that molecules change their random vibration to more in one direction (along a pipe) and less in another (perpendicular to the wall). They vibrate the same thermal way regardless of a net movement in one direction and the component of that motion toward a wall is unchanged by that directed speed. This is how vector addition of velocities works.
Orthogonal velocities do not affect each other. This is just like the classical physics example of a cannon-ball that has its horizontal speed unaffected by gravity and its vertical acceleration by gravity unaffected by the horizontal speed.
By this reasoning, air in a sealed jar that is shot from a cannon has altered vibration motions from when sitting still. This cannot be true.
For example, here is how velocities like this will add: A molecule moving thermally at some instant with a velocity at 45 degrees (up right) with speed (magnitude) 1.0 has an upward component toward a wall above it of 0.707 and a forward component to the right of 0.707. Adding a horizontal speed to the right of 5.0 results in a new horizontal speed component of 5.707 and the same vertical component of 0.707.
Velocities add vectorially.
The component of momentum perpendicular to the wall is unchanged. The air exiting any blower into open air is at the very same pressure as the still air around it.
This can easily be measured by anyone, just as it is by professional aerodynamicists every day as shown here in
Weltner, Fig 3:
user.uni-frankfurt.de/~weltner/Misinterpretations%20of%20Bernoullis%20Law%202011%20internet.pdf
Finally, the video completely ignores the presence of the well-known boundary layer which is completely motionless at the surface, so as a result, this claim of the molecules moving along the tube is completely invalid before even entering this above discussion.
*This is bad science.*
Observ45er, the video is correct. You may want to read the following.
physics.ucsc.edu/~ccrummer/aero1.pdf
Excellent explanation and illustration.
Thanks for the compliments.
Thanks this looks helpful for the AP physics 2 test this year.
Phenomenal! Very helpful as always!
Thanks.
This is the best channel on entire RUclips!
Thanks for the compliment.
Wow!!! You guys explain so well.
Thanks for the compliment.
Thank you so much! :)
This has bothered me for years and no one has been able to provide this simple vector explanation.
I am glad my explanation was helpful. Thanks.
Unfortunately, this violates some very common and well understood accepted principles of physics. It repeats the same errors that Charles Crummer makes.
..
The statement at 2:07 is correct. "there is no reason to expect an atom with a higher velocity to exert a lower pressure on the walls of the pipe."
There can be the same pressure in a fast fluid as a slow fluid. They simply have the same static pressure. Bernoulli is not about speed. It is about changes in speed or velocity which is Acceleration along a path.
The pressure on the walls of a sealed jar is the same regardless of the speed of the jar.
A fundamental flaw in this misconception at 2:42 is is that there no reason to expect a molecule to have the thermal vibration in only one dimension. These pressure causing vibrations are random in direction and are how they bounce round between other atoms.
At any given instant a molecule may be going down and the next at 90 degrees or even 180 degrees to the previous vibration.
That simple fact breaks this false logic.
..
Then. . .
It is the *average* velocity (over time) that has a directed motion when the kinetic energy is added to produce an increase in speed. That directed velocity is vectorially summed to the random vibrations. This is vector addition of velocities. This means that the random vibrations are superimposed onto the linear velocity along the tube. This is fundamental physics. Vector quantities like speed and acceleration add vectorially.
Ignoring that fundamental physics is another flaw in this.
..
..
Then, the added kinetic energy in the moving fluid is in only direction. It is not increasing the random thermal vibrations. That would require increasing the temperature. This is another flaw in this story. Moving the fluid along the pipe does not raise the temperature.
Therefore, the statement at 2:23: "an atom with a higher velocity would have a higher kinetic energy and, therefore, exert a larger force on the pipe walls" is false because it conflates / confuses thermal energy and momentum in one direction.
..
..
Consider bouncing a ball on the floor. Each bounce imparts some momentum to the floor. The ball's actual motion is only vertical..
Now, start the room moving (a train car) and the ball still imparts the same momentum to the floor with each bounce. It's actual motion, relative to the stationary ground changes. It has the *SAME* vertical component, but now a horizontal component vectorially added to the vertical motions. The pressure on the floor does not change.
.
However, these two motions are orthogonal and have no effect on each other. The vertical up[and down bouncing component remains the same. ONLY the ground referenced horizontal component changes as the speed increases.
This physics does not change if the ball is bounced on the ground outside the train's window.
.
This fails on these fundamental physics errors.
YESSSS thank YOU! This is what I've been asking and trying to explain!
Glad my video was helpful. Thanks.
As awesome as always. I love your videos very much!