Thank you

michalchik the pressure in the tubes is independent of the ambient air pressure and quite likely to be significantly higher. The only thing that can be said is that the pressure in the narrow tube is lower than that in the wider tubes.

Four years and no reply to my corrections...

Now explain the physics reason for that. . .

Bernoulli's *Equation* CAN be applied in open air when the total energy at the two locations being compared is the same. This can actually be done to compare above and below a wing. . In easily done demonstrations and ordinary flight, air is close enough to being incompressible that assuming it produces negligible error in the calculations.

@@Observ45er That is not Bernoulli's principle. Calling it Bernoulli is misleading. It's vapor dynamics. Anyone who designs aircraft will tell you that. The principles are similar, but vapor dynamics is a LOT more complex, which is why it has to be modeled in an wind tunnel. Also, WHEN air is compressed, there are other factors involved (electrical issues) that don't occur with liquids. Please read the definition of Bernoulli's principle. It was NEVER intended to be used with gases. We've had students do several demonstrations to show how Bernoulli cannot accurately predict air flow, in a very non-negligible way.

@@ezfzx it is same with air ( closed system) even though it is compressible. In woodwind musical instruments such as french horn , tuba ,trumpet , saxophone,clarinet...there is a constriction where the mouthpiece is and the pressure in that constriction is low.

@@snrnsjd Bernoulli's equation loses it's ability to predict pressure and velocity within a system when the medium is compressible. Continuity expects that whatever the volume of material enters the system, also exits the system somewhere else. When the medium is compressed, it's possible to add volume in one place, without losing the equivalent amount elsewhere. This results in a rise in pressure (and temperature) inconsistent with Bernoulli's equation, especially with regard to energy. Another way to look at it is that Bernoulli's equation is an application of energy conservation, but presumes constant temperature. So, it leaves out terms related to thermal energy. It is possible to write an energy conservation equation for fluid flow that DOES account for thermal energy, but then it's not really Bernoulli's principle anymore is it? Also, as mentioned, introducing compression in the problem makes the solution decidedly non-trivial, involving partial differential equations and/or computer modelling. Daniel Bernoulli was an excellent mathematician, and could have conceivably pulled it off without a computer. But he didn't.

Exactly

He has much correct here because he understands that pressure causes fluid acceleration (in the general sense of a change in velocity), but makes the common error of speed alone causing a pressure decrease for the Bunsen burner and gas torch. They are due to entrainment. Once the gas leaves the jet hole, it is at AMBIENT pressure! . Bernoulli is happening through the nozzle. . Starting INSIDE the nozzle where pressure inside is higher than ambient and slow moving, to OUTSIDE the nozzle, where speed is increased, but its pressure is the AMBIENT PRESSURE!! The gas exiting the nozzle entrains the surrounding air to form the fuel-air mixture. . The fuel and Air have viscosity with each other. Viscosity can be considered like friction between the two layers. That is called entrainment. The Jet of gas does not have a pressure lower than the air around it!! NOT! . It is so frustrating to hear this misconception repeated over and over and over.

Whether is is gravity or the curved paper as a spring makes no difference. . The fact is that the fast moving air out of your mouth does not have a lower pressure that the still air. This is well known by aerodynamicists and is easily measured with very simple equipment. . It is the fact that the surface disturbs the entrainment around the blown jet that a pressure reduction occurs as the air passes the convex surface. Once the paper becomes straight it is only entrainment that hold the paper up. Saying that fast moving air causes it to have a pressure lower than the still air near it is completely false and repeated by so many amateur scientists that have no understanding ot this. .

@@Observ45er I think you are overcomplicating younix258s point. I would try to explain it to you but it is already simplified to the point that I don't want to insult your intelligence by simplifying it anymore. You just overcomplicated something simple. It happens.

@@paulweston8184 Paul, Please put your words to what you're thinking. You won't insult me. . I always like to hear how others would explain things. It helps me better understand the terms others think in. It helps me explain things better going forward. . As an experienced engineer, as well as teacher, it's normal for me to discuss things for a better set of words to explain things and I prefer to understand how others think so I can do better "talking to them" [or others like them in the future]. I've heard all the common misconceptions and every so often run into a creative new one. . . , Looking over that last one, I see I did a poor job with those words. . While 258 is correct that the vertical-straight paper demo is disingenuous and the vertical-curved paper would still lift, that is Coanda which also causes a lower pressure along a convex surface flow. .' Are you going to say that Bernoulli's Principle 'explains' the blow-over-paper demo?

Thank you

But it is not correct. as I outlined in a comment, this video is a better one, but still has problems.

That is correct. It is NONE of Bernoulli. The air out of as blower is at atmospheric pressure. .

Yes that's fine.

The pressure reduction is due to the area reduction. This principle is used in so many millions of different systems that the Bernoulli equation will have been validated a million times over in the time it took you to watch the video. In the case of a venturi the low pressure will be in the throat. In the case of an orifice plate the lowest pressure will be slightly downstream of the orifice because that is where the vena contracta will be found.

@@Observ45er Ahem...Force/Area**

Thanks. Major brain slip. Reads better flipped around anyway.

The bottleneck creates back pressure in the larger area... having to squeeze through the smaller area makes it squeeze out faster... making the pressure lower... no back pressure... like when you put your finger on a water hose... the water shoots out... no more pressure...

@@MRGF78 So simply put, the pressure is *behind* the water in the smaller area of the tube, not within.Because the pressure wants to equalize, its going to push more water into the lower pressure zone.

It applies to the example of an open system. In a closed system like a plumbing pipe/or hydraulics: if you have a large pipe to start and reduce it to a smaller pipe in hydraulics; the pressure goes up and the fluid can reach a higher point, in a closed system like hydraulics or steam technology. One discipline to the next does not have the same opinions on these laws. They should stop describing these things as laws, and start describing them as workable theories. It's almost a cult, from one science to the next, of their forced doctrine and insistence that what they say is fact. None of it is fact, they're just workable theories: that can be used in different ways, and demonstrated different ways. Change the parameters and the so called law doesn't apply anymore; like in hydraulics(in a closed loop system of a plumbing pipe or hydraulic pipe) this doesn't apply. It doesn't apply in hydraulics because it's closed loop. IN hydraulics you lower the diameter of your pipe and it raises the pressure of the fluid which makes the fluid go higher. So to prevent your mind from getting twisted by these so called "cult" members who are teaching you they're particular doctrine. In your mind, change the concept of it being a "strict law" to it being a WORKABLE THEORY, until somebody else comes up with something better. I'm not saying it doesn't work the way they describe it, and isn't appliable and useful. WHAT I'm saying is don't get stuck into thinking that: it is a so-called law of fact. Change your mind into realizing their workable theories that apply to SPECIFIC PARAMETERS, but are not in any way a law: just a workable theory providing the parameters allow it to work. Change the parameters and the situation changes. A valid example of this is Tesla's AC motor from DC motors; which nobody thought would happen. Took me 30 years to figure out that: all Tesla had to do was remove the commutator from the DC motor and the motor naturally produced alternating current. The DC motor has a commutator which "alters" alternating current to DC artificially; by having it all go in One direction via the commutator. The same effect could be done with a full bridge rectifier instead of a commutator. All confusions of any subject you're studying is the subconscious realization that: it doesn't match up with other theories or so-called laws. Because in those other so-called laws or workable theories the parameters of the experiment have changed. Then they push their theories on you as so-called "laws" like a used car salesman, in the hopes that you get completely brainwashed into submission, to their cult/ empirical scientific proof. WORKABLE THEORIES as a mindset will help you figuring stuff out. Never accept any of it as law. Because someday somebody will come along with yet another theory; that will show how it can work a different way. Education is brainwashing. Wisdom is the ability to discern the differences. I hope this helps you.

@yazmeliayzol624 Wow. First time I got a positive comment. Cheers.

The arrows show the direction of the FORCE also called a Pressure Gradient. The arrow points from the higher to the lower pressure because the acceleration is in that direction - the same as the force. This is simply Newton working in fluids. Air has mass and follows Newton's Laws. He is clearly one of the few people who understands the true physics - - THOUGH he messes up with the Bunsen burner and gas torch where he makes the common error of thinking the jet has lower than atmospheric pressure - it DOES NOT!. The gas entrains the air around it to form the fuel-gas mixture.