Bernoulli's Principle Demo: Venturi Tube 

They Only use 3 props,one is black board, other is duster and chalk.

Schools are just meant to teach you values of life while the actual study is to be done by yourself! The more quickly your country understands it , the less problematic your school issue will become !

@@Lalo-Salamanca. If by values of life you mean ‘moral values’ then I don’t agree. Value systems should be developed by people themselves.If anything, children can be put into diverse environments to develop their own values. Same can be said about any other form of education, providing the best environment to learn something is what’s important.

Thanks a lot....No one explained it so nicely as u did.

@@AuMechanic Perhaps, but THE "Bernoulli's Principle" equation, as taught in first year physics is most likely the one people will have in mind when they search for and find this video. Ironically, Bernoulli's equation was actually formalized by Leonhard Euler, about the time when Giovanni Venturi was only 6 years old. See, most non-physics majors taking physics will only ever see this one equation or hear about this one element related to Bernoulli, and still misunderstand THAT, when the explanations and special conditions regarding this principle and equation are not clarified. They're oblivious to extreme exceptions and corner cases. They will never know about Bernoulli's family life or other contributions. And they will continue to point to air-flow examples and squeal "Bernoulli!" inappropriately, without understand why, or why it's inaccurate. They will also never become familiar with all of the other contributors to fluid flow dynamics, the work of many of which is far more relevant to current applications in aerodynamics and hydrodynamics. The point is ... if they're only going to ever learn this one thing about this one guy, let us (as instructors) get it right.

@@ezfzx Thank you for bringing happiness to our lives.

In Fluid Dynamics at Mach number < 0.3, airflow is considered incompressible. So we can use Bernoulli's Equation in such a case. Correct me if I am wrong sir.

@@Lalo-Salamanca. Respectfully, my concern is this. There are far too many air-related demos that are described as Bernoulli, which either are simply not, or, at best "Bernoulli-adjacent". So demos one my colleagues did with open air flowing over the top of liquid-filled pipes from different directions had some very interesting and unexpected results which were inconsistent with Bernoulli's principle. Our department has a Venturi Tube demo like the one you're showing, and it's good to see the lower pressure, pressure differential, etc. (We also point out that Venturi came along about 50 years after Bernoulli.) My point is that any air-flow effect cannot be just attributed to Bernoulli without at least some kind of disclaimer. Bernoulli (the guy) was very clear about the conditions of his equation: incompressible, inviscid, laminar flow, closed system, no added energy. We can perhaps dismiss the slow air as approximately incompressible, but not the rest. Even slow moving air behaves differently moving into and out of a pinch, as we see in wind tunnel tests. Even the A/C repair people can tell you that. You can see where the dust piles up from the gentle turbulence. Academically, for students who don't continue to study fluid flow for a living (aircraft designers, for example), it becomes very easy for them to make this one association without appreciation for the nuanced exceptions, and should they go on to become teachers, simply recite it like gospel, perpetuating the misunderstanding. (I've had high school science teachers, who never worked in industry, try to argue with me about it, until I show them a few demos that contradict their understanding. That's the nice thing about physics ... I don't have to argue; I can just show it. And I'm looking for a video to show you too.) The demos are fun and exciting and amazing, so-much-so that it's tempting to perform them without the details, just to wow the crowd. However, for the scientist/engineer, there's something deeper and exciting going on, and it would be disappointing to miss that opportunity.

@@ezfzx Thats fact. If we aren't involved in it for a living, we take things in approximation. I understand your point sir !

Also having the same question here

Check out the concept called continuity in fluids

Yes the amount of air per unit time sounds like the volumetric flow rate. As far as I can tell it's the same thing. It must be that sometimes a volumetric unit of a gas means the amount of it that occupies the unit volume when at standard pressure and temperature.

The easiest way to understand why the pressure is lower in the narrow part is that an element of fluid in the wide part must accelerate as it approaches the narrow part (because conservation of mass requires this). The only way for the fluid element to accelerate is if the pressure is greater behind it (in the wider part) than in front of it (in the narrower part), creating a net pressure force on the element that causes it to accelerate as it approaches the narrow part.

Physics Demos makes sense that there would need to be a pressure difference, so does that mean that the larger tube gains pressure, or does the smaller tube lose pressure, if you know what i mean? I would instinctively think the large one gains pressure cause all the particles hitting the bottleneck would sort of pile up on each other, and force the air through the small hole, but once it gets going through the hole, the air is able to move freely again and return to normal pressure since nothing is blocking it anymore. So if you added another tube comparing the small section with the atmosphere, would the small tube be the same, if not slightly higher pressure? Also thanks for replying

@@buzzmas8068 The pressure buildup from the particles hitting the bottleneck is a good way of thinking about why the pressure is larger in the wider region, relative to the narrow region. You can think of it either way - larger tube gains pressure or the smaller tube loses pressure. None of the pressures is "normal."

@@physicsdemos This is one of the better demos because it shows the static pressure rise in the first wide section when flow occurs. .. What I don't understand is why no one addresses this increase as caused by the restriction effect of the narrowing of the pipe. The fact is, that the restriction is attempting to reduce the flow and, therefore, *causes* the increased static pressure in the right hand wide section. The fluid is not being squeezed in the narrow section, it is the outlet that allows the fluid to "escape" the higher pressure section. .. Think of the wide inlet section as a pressurized tank with an outlet that is relatively small. The pump is forcing high pressure fluid in from the right. This is a characteristic of a constant flow system, or pump. Everyone just says "Conservation of energy" and that the energies in effect exchange places as cross section changes. I find that to be disingenuous, or at least incomplete. If no energy is added or removed, and the fundamental setup prevents and energy change, then this is a given, not a cause, . .. Air has mass and we know, ever since Newton, that a force is required to accelerate a mass. Therefore, there must be some force/pressure causing the acceleration and it is our responsibility to explain that pressure. .

+Buzzmas , Here's WHY .. All pressures mentioned here are static pressures. .. The narrow section is not squeezing the air because it's free to exit on the left. .. IMPORTANT: NOTE that the pressure in the right wide section INCREASES when the flow starts. This is very significant. It tells us that something is restricting/resisting the flow above and beyond the atmospheric pressure at the left. THAT resistance is caused by is the NARROWING entering the narrow center section. The narrowing increases the pressure UP-STREAM. . With a higher pressure there, the narrow section is now an outlet which allows the air to escape. Think of the right-hand wide section as a pressurized tank. The narrow section is now a hole in the tank letting air escape. .. If you started with a *completely wide* pipe exiting into the atmosphere, it would be atmospheric pressure at the left and pretty much atmospheric pressure all along the length of an all-wide tube. ... If you could vary the cross section of an all-wide tube, you would see the pressure on the right go up when it was narrow in the center or anywhere down stream.. .. Help?

You Helped Someone Thank You

@@Ram-xy2vy yay!

@@lucasdasilva8697WOOO!

According to the continuity equation (A1*V1=A2*V2) when you cover the opening of the hose the velocity of water increases. When a high velocity object hits a barrier the force acting on the barrier is high compared to a low velocity object. Pressure= Force / Area. As the area is same in both cases you *feel like* the pressure is high when the water hits your hand.

I don't know.

may be low pressure, low density, thus molecules are not that active...like in the upper atmosphere of the earth low pressure thus temperature goes in "-Celsius"...may be i don't know.

If you look closely, the liquid in the third tube rises a little. This could be because the velocity of air in the second wider section is higher than the first wider section as the air is coming from the thin section (where the air is travelling at the highest velocity). This causes the liquid in the third tube to rise a little bit, but not as much as in the second tube.

My assumptions is that it is because the third tube is near the exit of the duct, and is therefore closer to the atmospheric pressure in the room, which is the pressure inside the tubes when the flow is turned off. This might explain why the height of the water columns doesn't change as significantly.

Sure. If I shrink down the middle section until it is only big enough to fit 1 atom then the pressure is only equal to the kinetic energy of 1 atom right? And now because only 1 atom can fit in there he does not have to worry about bouncing into some other guy and losing energy and wasting time in the tube, he has the highest possible throughput. The wider the tube the more atoms go in there, which makes it harder for them to get through. They all keep bouncing around.