Bernoulli's Principle (Venturi Effect) | Pressure

Bernoulli's Principle (Venturi Effect) | Pressure
Form 5 Physics KSSM Chapter 2 - Pressure

1. Bernoulli's Principle states that as the speed of a moving fluid (liquid or gas) increases, the pressure within the fluid decreases.
2. The Venturi effect is the fluid pressure that results when an incompressible fluid flows through a constricted section of a pipe.

[lixuantan]

Thanks for letting me know that venturi effect is actually an application of bernoulli's prinicple.

[Observer]

@
Mrjcraft00 For some reason, your whole comment won't show after I initially read it. ... but.
You're getting close.
In the above video he explains what happens and that is consistent with what Bernoulli said, but doesn't explain cause and effect (neither does Bernoulli's Principle state cause and effect). This vague talk about conservation of energy, while true, does not explain why the pressures are what they are.

Where the pipe narrows, this is a restriction that impedes the flow coming from the pump and that raises the pressure *up stream*, TOWARD the pump.

The narrow section, or nozzle is NOT squeezing the fluid. The place where the cross section is decreasing, is preventing the fluid from escaping to the narrow "outlet". It is making it more difficult to flow.

The pressure toward the pump is caused to increase because of the restriction.

If there was no narrowing, there would be no restriction to the flow and the pressure would be lower. When the diameter is reduced at the nozzle, the pressure behind it increases.

The narrow nozzle then allows the water to escape into atmospheric pressure which is much lower.
The narrow section of the classical venturi as shown here is the same thing.
..
If we see some mass such as that of water in a pipe and it accelerates, as at the nozzle, or by the harrow section of pipe, we must figure out where the force comes from that is causing this acceleration.
That force, called a Pressure Gradient is the source.

For the venturi, think of the large section as a pressurized tank and the narrow section as an outlet. The higher pressure pushes out of this outlet toward the lower pressure.

In the mid 1700s, following up on Bernoulli's work, Euler determined that a Pressure Gradient provides the force that accelerates fluid.

Just like the nozzle, or the finger over the end of a hose, the following video by Enbin Zheng shows this very clearly with a pressure measuring manometer right before the outlet as it changes diameter from large to small...
Enjoy
.. .. ..
Also... NO! it is *NOT* the fact that they are pushing more in one direction that they push less in another (at right angles toward the wall). Static pressure pushes in all directions equally. Euler also determined the concept of pressure at a point. Pick a point and the sttoc pressure is pushing on it equally from all directions. If you move along with that flow and measure pressure, it is decreasing in all directions as it enters the narrow section of either the venturi or nozzle.
The pressure *behind* it, in the larger section is higher, pushing more and accelerates the fluid toward and into the narrow section where there is a lower pressure - as it 'escapes' the higher pressure "tank".
.
Your reasoning for the following is incorrect: " If the pipe is constricted, the cross section area goes down, but pressure remains (in comparison) relatively constant, thus the force of the water must increase."
If pressure were to remain constant for a smaller area, the total force decreases. Force equals pressure times area. When area goes down, force does also. This is why a small area piston on the hand-pump of a hydraulic system can lift an auto. The piston for the auto has the same pressure but a large area.
.. ..

If you want to think about the bouncing molecules, when you add velocity in, say the horizontal direction along a pipe, it does not change the random molecule motions and, therefore does not reduce the vertical motion toward the walls. The random motions just "ride on top of" the average motion in one direction. Velocity adds vectoraly, so a horizontal increase does not change the vertical velocity.
The random, Brownian motions are unaffected by the average speed down the pipe.

This is just like bouncing a ball in a car. The ball bounces are the same whether or not the car is speeding down the highway.
.
This is also analogous to the classical cannon ball shot. The vertical acceleration and resulting velocity changes due to gravity are completely independent from the horizontal speed, ,
The horizontal speed remains constant an is unaffected by it's changing vertical speed changes
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SPEED ABSOLUTELY DOES NOT CAUSE A STATIC PRESSURE DECREASE!

Your post:

"I thought about this for a while, and I think I had something click that might help explain this. First let’s assume over a small section of the pipe the pressure remains relatively constant. Pressure losses are usually due to friction which isn’t substantial over a small section. If the pipe is constricted, the cross section area goes down, but pressure remains (in comparison) relatively constant, thus the force of the water must increase. This is why fire nozzles narrow the stream and create such strong forces. This increase in force accelerates the fluid, and as the particles of water accelerate in one direction less of them will fly in other directions, exerting less force on the walls, creating the Bernoulli and by extension Venturi principles."

[engineermuhammadkashif]

Awesome lecture
I'm a teacher my self and I take help from YouTube channel as well as Google
It's a good methodology
Thx for the explanation

[xm_mx]

I suppose fluids (gases and liquids) behave similarly in that they flow from high pressure to low pressure.

[elgalactico]

Thank you ! I seriously was like what’s the difference between Venturi effect and Bernoullis theorem

[naif]

Thank you for making this concept verey clearfaction

[dermdoc]

After so many videos finally came across one I understand thanks from USA!!

[jaysmith]

Where is the math?
How did you conserve momentum?
Where did your pressure go in p3? Into p1? Your putting more pressure in p1 due to viscosity or density or what factor of logic have you considered, or did you just draw this with nothing worked out?
I consider the probability of that matter is hardly enough to split this reality into a quantum duality apart from my certainty, entirely without quantization of any further observation. 🤷‍♂️

[furulevi]

How can the pressure be lower in point B and the speed be higher ??
This is like saying you are using less energy when you are running, and more energy when you are walking...

I haven't experimented with this, but in my opinion the pressure in point B is not lower just because the water level is lower in the vertical column. If water is forced at a high speed to the right, than it can't change suddenly its direction and go upwards too...

[Couckey]

Omg THX for the help :) the best teacher

[dftba]

nice explanation.. u r from which country?

[josemathewroble]

Awesome! Really explained the concept to me simply and effectively!

[fetB]

funny how everyone says, it's just low pressure because someone said so...

[happening_]

1:05 you can't just explaining that by repeating the same sentence.😂

[Jennzzzzzz]

Hi! can you give me some explanation why bernoulli's principle is related to vacuum. Just for my study

[Andres]

This video was very useful and didn't make the error of saying that it creates suction; that made all the difference.

[aimanzaidi]

For the uniform tube :
Why A to C
Pressure decrease, velocity increase
However you said that friction of the wall cause pressure decrease. Hence you are saying that the velocity increase. Why friction increase velocity increase?

[kadodae]

Thank youuu for helping me to understand 👌🏾🌠

[Observer]

If the fluid speeds up, this is acceleration and requires a force.
*Where does the force come from?*
Accelerating a mass requires a force, Per Newton's First law...
Please answer this.
You seem to say that the pressure is lower because Bernoulli says so..?..

[keely]

omg I love your accent!! I wish you were my teacher!!