Venturi effect and Pitot tubes | Fluids | Physics | Khan Academy
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- เผยแพร่เมื่อ 31 ส.ค. 2014
- David explains the Venturi effect and the role and function of Pitot tubes.
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This is really cool. It's so counter-intuitive that a fluid passing through a smaller space has decreased pressure, but it's super easy to test with a hose.
Lower static pressure the dynamic pressure increases actually
But how if we put hand against fast fluid it will exert higher force than slow fluid .
@@captainamericawhyso5917 what is the difference between the two?
@@dhruvparmar4061 you have to imagine that the whole tube in the video is filled with water and it flows from left to right, the hand thing is not a good example because it doesn't compare to what's show in the video.
A much more intuitive way to show the Venturi effect is to show a section where the pipe widens, rather than narrows. If we double the cross sectional area, the flow rate (m/s) falls in half.
Excellent explanation. Extremely useful for engineering as well.
team FE prep, what up
@@jonathanstevenson8948 you and me are full of fluids, don’t you think these people studying blood circulation, blood pressure, and all kinds of bodily processes should know about how fluids work ?
@@theadel8591
All branches of science have theories that conflict with other branches of science.
In this explanation he claims that a restricted or reduced diameter pipe lowers pressure.
When you go to the doctor and get your blood pressure tested. He wraps a choke around your arm and inflates it with air reducing the amount of blood going through your arm or the constriction.
He then tells you, your blood pressure is 80 over 120psi. showing the resting blood pressure, and the active pressure. But that wouldn't be accurate if this above theory was correct.
Their measurements of so-called pressure would have to match the existing pressure in your arm but it doesn't.
It's measuring the pressure of a constricted area which in this case would be the center of the pipe.
So they're actually measuring the lowest pressure in your arm, but claiming they have empirical proof of what your blood pressure really is.
I've yet to see one branch of a science or discipline that doesn't conflict with the theories and concepts and held beliefs of some other branch of science. Not even doctors can agree, cuz they all have separate specialties.
So it's all theories and opinions, none of it is fact, And it's only a working theory as long as their so-called law has working parameters that allow it to exist.
Take away the working parameters of any so-called law and watch that law fall apart.
There are an awful lot of laws that require gravity, so if you do them in space the law falls apart.
This was Einstein's conundrum. He wanted a theory of everything. And the stuff worked on the small scale but didn't work on the large scale and the whole thing fell apart.
So as a student pay attention, these guys really have no clue what they're doing.
They just have a bunch of "Theories" they call "LAWS" that really don't work, but they insist you believe them as fact, like some kind of cult.
To pass their tests to get a degree, or a passing grade in a particular subject, you have to just blindly spit back the information that they give you: whether you believe it or not.
So it's actually not a knowledge test it's an intelligence test. If you're intelligent enough to question their fake laws, you get a failing grade. If you don't care about what they're saying and blindly believe everything they tell you you get it passing grade.
Order takers and sheeple get degrees in the academia.
Question whatever they're doing and you will fail your class.
By the way in hydraulics if you reduce the diameter of the pipe they claim in hydraulics that the pressure goes up. Over here in physics they're climbing that the pressure drops.
So in hydraulics: in a hydraulic line, if you reduce the diameter of the pipe from what it was before then you have a higher pressure, and it'll go higher up the pipe.
So in hydraulics they're not calling it more speed, they're calling it more pressure, cuz it goes higher up the pipe on a smaller diameter pipe. When the pressure stays the same but the pipe is reduced.
Like I said from one discipline to the next none of it adds up. None of them talk to each other and have a uniform theory across all disciplines.
The physics department does not talk to the hydraulics department, does not talk to the math department, does not talk to the science department, does not talk to the medical department.
Is this a fact that you claim proven by installing a pressure gauge at the reduced pipe section in the center?
The pressure will reduce not increase at the cone shaped part after the reduced pipe in center. did anyone bother to hook up a pressure gauge at the center and at the cone shaved part after the center reduced section?
Perform this test yourself and challenge this test. Do not blindly accept whatever they tell you as this does not match up to what hydraulics discipline says. From one discipline to the next they do not have a concurrence of belief system.
@@amandadube156 🔥
Thank you so much! Hard to find videos like this that actually interesting!
3:44 on top of explaining the pitot tube REALLY well, I found this portion super hepful also. It visually shows, via the equation, why pressure drops as velocity goes up. Amazing. I love how all the profs say it's counterintuitive, and it is, but this makes is visually clear.
Excellent explanation, thanks a lot. I'm studying about aircrafts systems and this video helped me a lot.
"THAT'S GOTTA LOTTA PRESSURE" I lost it when he said that, it reminded me of Phill Swift in the flex seal commercials.
Awesome vid, best explanation I've seen on this topic!
SO HELPFUL!! Thank you so much. Lightbulb moment.
Perfectly explained! Thanks :)
Excellent presentation. Very amusing all the way through. Thank you
amazing explanation, thank you!
Great explanation, thank you so much for the video!
This is really helpful, thanks a lot!
good explanation. Thank you so much!
It is very clear explanation ,, i really enjoyed it
Good job dude
Wow! Physics simplified ... I didn't know that was possible!
Excellent explanation! Thanks 👍
Very good explanation, I never really understood the Venturi how pressure would go down in a constricted space, i mean when you think about oil pressure in a car's engine, its because of the small holes oil has to pass through (constrictions) to create a higher pressure to lubricate the parts.
thanks from belgium
Thank you so much for explaining this.
Great job explaining Bernalillo equation. Thanks
Amazing, thanks!
Perfect Illustration
First year aviation student....teacher today was explaining carburetor icing and when she got to the point where she said that the restricted portion of travel has less pressure that the large volume behind it, my brain checked out. This didn't make any sense to me on a common sense level. This video explains whats actually going on very well. Thanks
Are you a pilot now?
Great one
Thanku for explaining 🙃
Great stuff ...
Thank you so much :)
The lower pressure is observed due to the differential pressure between the inlet side of the pipe versus the outlet side. So the low pressure zone is in the expanding area of the discharge side of the constriction. The inlet side of the constriction should have increased pressure along the walls of the taper moving into the constricting zone.
This effect can only be observed in a pressurized system so it's important to think of the system as a whole. Pressurized fluids will only move to a zone of lower pressure (when they aren't actively being compressed obviously) The zone of low pressure is often the open air. When the supplying force of the pressure encounters a restriction the overall pressure on the service side will be higher than if it were unrestricted. If the system is closed the overall pressure is at it's highest. If you open a valve the low pressure zone of the open atmosphere (or other lower pressure region of the system) will cause the contents of the system to flow and the pressure in the system as a whole will decrease. When you start to close the valve you constrict the flow rate and the pressure increases on the supply side as the valve closes. Fluid moves faster in the constriction because it is the first point of access to the low pressure on the outside of the system. The zone of restriction sets the flow rate for the material behind it. The material behind the constriction is a larger volume of material being dragged through a small hole, so naturally the cross-sectional area of the pool of material won't be progressing along the horizontal axis as fast as that of the restricted area.
A good illustration of the speed and pressure differential is an hourglass flowing. Although it doesn't directly apply unless you consider gravitational pull to be the same as a zone of low pressure, and gravity seems to be the opposite of that; even though sometimes it's functionally the same.
Is there any way you could do a video on a pitot tube that uses a mercury manometer?
Useful for medical biophysics!! Thanks a lot
medical biophysics? never heard of it. sounds cool.
Did David Cross just teach me fluid dynamics?
Great video
Thank you :)
Hey! I'm studying to become a pilot and struggled to understand this now I know🙃 thanks
thanks man
And the perpendicular intake is used for determining height of the plane, right? Because there is an atmospheric pressure in that second chamber, which equals P=P0*exp((-mgh)/RT).
Za ck they have other static ports for height
Taking the analogy of conventional electricity in wire, is low pressure the cause or the effect of high velocity here?
In pitot tube how the velocity of the particle in contact with the wall becomes zero. Initially it had some velocity. So in a long run the point at wall will be accumulated with large number of such zero velocity particles. How do u pls explain this.
nice explanation
So the output from the pitot tube ends up as the Air Speed indication inside the cockpit?
You save my life
Will the air in the upward hole on the pitot tube not be sucked out? Because air has viscosity. The air flowing horizontally carries away the air inside the horizontal hole due to its viscosity.
best explanation, didnt put me to sleep unlike my prof
really coooooooooooool!
So i get the point of the bottom tube, because you would get a pressure build up. But why does the top tube have a hole at 90 degrees to the air flow? What is the top tube measuring?
Eye of a hurricane or the like , is the 1st thing that came to mind. 🤔 seems like these tie together.
can someone please help me with a question... When comparing the velocity of blood flow through the arteries vs. the capillaries, according to the continuity equation, the velocity of blood is higher in the artery because the area of the artery is smaller than the net area of the capillaries. Then according to the venturi effect, the pressure should be the lowest at the artery, because it has higher velocity than the capillaries, but this is not the case. The blood pressure is the highest at the aorta in systemic circulation, can someone please explain why this is the case?
Dankieee😩
What software did you use to make this video?
that looks like MS Paint!
if the fluid is also the air, and if the velocity of the fluid is zero, can we then say that the static pressure is equal to the atmospheric pressure?
+jamesmasonic Yes. Just need to consider the flying altitude and adjust both density and pressure.
Love this guy lol
In the pitot tube ,does the air enters in the top chamber?
The pressure is referring to the outside pressure! Speed increases moving from high to low outside force
In the last part, to workout the Velocity from Pitot tube, how would we find out P1??
i think its too late to answer :D ,but P1 is atmospheric pressure!
Does it mean that when fluids went through the narrow portion, reach the other side, the pressure will increase again?
Yes. 😊
Khana teaching me better then professor 365 days a year.
nice
In the second example, wouldn't the density at point 2 be larger than that at point 1 as the presure is larger and air is compressible. Thanks.
Not at common speeds. Below about Mach 0.3 it is pretty much not compressed enough to make any difference.
YES, YES, YES, and that's why Bernoulli's equations only apply to liquids, not gases.
hi i am studying for my red seal boilermaker exam and do not understand how to work out the answer so i was wondering if you can help
Calculate the differential pressure developed by an open venturi tube measuring air speed at 50 MPH,at sea level (ρair = 0.00235 slugs/ft3), where the throat diameter is one-half that of the entrance diameter:∆P50 MPHairAlso, how much pressure will the venturi tube develop at twice the air speed (100 MPH)?
lisa N michael fleming wtf is slugs
Is pressure directly proportional to temperature ?
If you use air instead of water
would the smaller tube get colder ?
Does the angle of funnel tubes make a difference ?
Yes the air can get much colder. Look up the effect of "Carburetor Icing".
While it can cool air it's also a restriction. so if your next question is can you use this on an Automotive intake to cool air. I would say the gains would not outweigh the potential losses.
@@lliaolsen728 Thanks Llia for your prompt reply !
Its not the added speed that decreases pressure, but the lesser volume. Two streams of equal volume but different speeds will have more pressure on the higher speed stream. When the pipe is reduced by, say half, the volume at any given point is half but flowing twice as fast. Its like the difference in a high velocity, low mass bullet and a low velocity, high mass bullet. The one with higher mass requires greater energy to stop and therefore has greater force, if we assume exactly half velocity and half mass. So in the half inch pipe, there is half as much surface area of water as in the one inch. Just like a hydraulic jack in reverse. The stream in the small cylinder travels further in proportion to the large one and with a proportional fraction of pressure. Ten pounds in and one hundred out. Reverse: one hundred pounds in, ten out but going ten times the distance.
+bg81973
What you refer to is the dynamic pressure of a faster stream being higher. This is the pressure you see when that stream comes up against a surface that stops it. It is hitting the surface, thus pushing more in the forward direction.
.
The pressures in a venturi talked about here are the static pressures. This is the pressure you would feel if you were traveling along with the fluid and it is not hitting you. This is the pressure felt on the sides of the pipe.
.
Also, a slower, but higher mass bullet can have the very same energy as a faster, lower mass bullet. So your analogy is also incorrect. The momentum is mv - Mass times velocity.
..
Your hydraulics analogy is also incorrect. Hydraulics is a static based system of pressures. The idea is that the pressure is the SAME throughout. It is the FORCE that then varies with area. Force equals pressure times area. Smaller area less force - Larger area, more force.
But how can we use Bernoulli's equation on air if air is compressible? Density of air can change
Correct. The density of a gas is dependent on its pressure and temperature. Bernoulli's equations relate to LIQUIDS, not gases!
how come high velocity gases exhibit this behavior?
Means thanks.😁
what happens if the pitot tube is directed opposite direction of the aeroplane flies?
But isn't the water at higher pressure in the constricted part? Hence pressure washers producing more power from and pressure from a smaller nozzle than a larger one?
No, on this case increased velocity means decreased pressure. Conservaton of energy explains that. The pressure washer gives a high _velocity_ of water out of a small nozzle for exactly the same reason, going from (relatively) high pressure in the hose to low (atmospheric) pressure as it leaves the nozzle. It is the pressure of the water that converts to kinetic energy as the pressure drops suddenly (see the concept of PV work).
I guess thats how they calculate the air mass flow of engine manifold with map sensor
lol, ok, I watched the rest of it, you just explained how a bulgarian 4 piece flash suppressor/ booster works
perfect, got exam in 2 hour and confused with books
had me at good day ..lost me at p1
I love you.
2:06 why do we care? well, i can answer that for you uhhh i wanna be a doctor!
Doctor yet?
@@jonathanstevenson8948 nah bro being a ferrari fan gave me tuberculosis im on my death bed right now
Well, then how do we know how much is the stagnation pressure?
6:49
This guy is so much better than Sal.
5:40 But isn't air compressible?
Edit: Nevermind, seems that for speeds below Mach 0.3 air is treated as an in-compressible fluid.
Yes, you got it.
Yes, but that's not true. The compressibility of air has nothing to do with its speed! The density of air is dependent on it's temperature. The
why is the height ignored? there's such a big difference :/
I think you're missing the fact that the venturi tube and pitot tube, both work on a drop in atmospheric pressure. There is no "stagnant" air in the tube. It is at that point that pressure is reduced the most because there is no air and no atmospheric pressure. Thus, atmospheric pressure acting on anything attached, being about 15 pounds per square inch, will force it into this space. Likewise, the stagnation in the pitot tube is not by volume but a combination of pressure in the lower chamber and vacuum in the upper. This vacuum is the result of drop in atmospheric pressure as the air crosses over the opening and sucks the air out.
This is poorly worded, so it is impossible to tell what you are trying to say, but the first sentence is incorrect.
I suspect you are confused about how the pitot tube works.
One port of a pitot tube has stagnant air, the forward facing one which has a pressure that is higher than atmospheric pressure and is called stagnation pressure". Air is being rammed into it, thus increasing the pressure.
Air is NOT sucked out" of the static port of a pitot tube; that port is at the surrounding, unchanged atmospheric pressure called 'static pressure'..
Therefore, the pitot tube operates via the increased pressure of the forward facing port (which is stagnation pressure) vs the surrounding atmospheric pressure in the static port on the side.
Is this for iit jee
Any brothers here from that mcat question about the venturi mask?
The way you write the letter P is absolutely ubsurd
@ 6:39 minutes/ seconds: you claim stagnation at center. Was this ever tested by a smoke test showing the smoke flow of all areas you mentioned. Whenever I've done such a smoke test it shows the air flowing up or down with a stagnation point at the wall sometimes in the form of a vortex spinning around at the wall only. The rest of the air you're claiming is stagnant gets drawn up the wall,by the slipstream of the air above and the air below which drags your so-called stagnant air up or down. You can test this for yourself by simply putting a fan in front of the wall and running smoke through your apparatus to test where the air actually goes.
itsa a gotsta staysa the samea!
Хвала брт.
The thing is that you cant use Bernoulli's equation for Air!! It is not incompressible!!!!
How can we spread the news when even NASA spruiks the same nonsense?
Motorcycle performance exhaust systems
Add toogi colors
I wish physics would be applied to road traffic..
If the people acted as one unit it just might. However people are a-holes and follow too close or stop others from merging so it gradually slows the process to a halt. On a freeway or Highway. The fast lane ( Left lane(s) in the US) is considered the cross section or center line of the venturi. The onramps and offramps are the dimensional changes from 8 lanes to 4, the first two of the four lanes closest to the divider barrier are still the center of the venturi, call them lane 1 and 2. To decrease the pressure the cars in lanes 1 and 2 would have to increase speed from 50mph to 70mph leaving greater spaces for cars to merger between them at high speeds. The cars merging from the 7th and 8th lane onramps would have to speed up from 30mph to 70mph and make the same adjustments to increase following distance as they move from the outer most lanes approaching lanes 1 and 2, thus maintaining high speed at lower pressure.
.. there is also a 3 main rules making traffic flow as in venturi.
1. Speed has priority.
2. Passing happens only from left.
3. Slower moves to the right.
The equation is the explanation not the cause
Who else watching this video in 2024?
or light! we have already done it
I find amusing when people teach and use statements such as this happens due to the Bernoulli equations or such natural process obeys such equation, utter nonsense. Thing don’t follow equations equations describe what is happening. But if you said the process is obeying the underlying physics that would be a better answer
i fell a sleep after 8 mins
Rho the Greek letter is not drawn like a p. Think łłłłłłłłłľľľľľłłłłłł
This is very disappointing to hear from the Kahn Academy. The reduced pressure is NOT "due to the equation".!!.
The in crease in speed (acceleration) is DUE TO THE PRESSURE GRADIENT!
wow, so a pressure washer is a low pressure washer
Nope! The pressure of a high speed stream is using the DYNAMIC pressure. This is the pressure of the high speed stream hitting something that stops it. That fast stream of water actually has a static pressure that is atmospheric pressure - the same pressure as the air it is pushed into by the HIGH pressure inside the tank and hose.
One needs to understand the difference between static and dynamic pressure.
He doesn't make much sense. If the water can't flow through the restricted / narrowed section 'on a higher speed' , the flow elsewhere in the pipe will simply slow down, his explanation suggests things on the forehand we don't know. The tap is a similar restriction / narrow spot in you water line, and it DOES slow down the water in all the rest of the tube / pipe, whatever you want to call it.
pee toe tube
Nonsense!
+Nihar Baijal what the fock?
This film
This was not an excellent explanation. It was boring and not easily grasped, though everything you said was easily understandable.
This video should show many real world examples/pictures/videos of venturi meter, with the "Madden highlight pen"