Bernoulli sometimes sucks; explaining the Bernoulli effect: from fizzics.org

The Bernoulli effect is wrongly used to explain many simple demonstrations within YouTube and on the web . The video gives examples of several demonstrations and aims to provide logical explanations together with some practical examples of the applications of Bernoulli's and Venturi's effects.

[snrnsjd]

2:10 That's a false assumption to think that the paper should go down when you blow across the bottom of the paper. Paper is in the way of air, so it pushes away. As someone said in the comments , put the paper vertically and blow on the left side or right side and you will witness that it bends reasonably ( not extremely like gravity or whatever pulling it down) where you blow air.

[younix]

I believe the comparison at 2:10 is not an apples-to-apples comparison and the explanation you provided just sort of hand-waves the proposed explanation away.
When you hold the paper horizontally, gravity comes into play. When you blow above it, you have a paper flexed away from your air stream being pulled towards the velocity vector of the air. When you blow under it, the paper is now curved to cover the stream and gets pushed by it.
A better comparison would be to hold the paper vertically, curve it to imitate the first situation and blow on the opposite end (basically turning the experiment 90 degrees sideways). Then if conducted properly, the Bernoulli effect would apply properly on either side.
Try it yourself and you'll see.

[octavstanculescu]

You are demonstrating a lot more Coanda effect than Bernoulli

[dn]

It's more Henry Coanda than Bernuli with pressurised air following a curved object.

[k.chriscaldwell]

Lift by an airfoil (wing) is NOT Bernoulli in nature. It is Newtonian. It is the vacuum created on the back side of the wing that pulls down air from above, accelerates it, and then shoots it down the wing’s trailing edge—opposite and equal.

As lift by an airfoil is Newtonian, it is noteworthy that gravity provides the vast majority of the energy that sustains a plane, or helicopter, in flight. Hence why planes have glide ratios, helicopters autorotation. Airfoils, in a way, are gravitational energy harvesters.

[thanhviendhh]

At minute 1.05, how can we calculate whether the flow from the small oogns will fill the large pipe?
What if the pipe diameter is too large?

[JCnordic]

It's a physics of false opposites. Air is mass, so less air molleculles would intern be low pressure, air molecules can travel faster, less resustence

[ofcv]

I THOROUGHLY ENJOYED you video, well done!

[jens-eriklangstrand]

basic error at 1.46 ..ok pressure vectors .. not good illustration though ..

[ezfzx]

Bernoulli’s Principle applied to laminar flow (not turbulent flow) of incompressible and idealized inviscid liquids (not air) within a closed system (not open atmosphere).

[Ethan-uofv]

2:16. Re-think that one. The kinetic energy of the molecules blown against the bottom is partially transfered to the paper, because the paper is in the way. When blown across the top, the paper is not in the way.

[michalchik]

Roger Linsell 

Interesting video. I have always thought tat the BE was being misapplied in a lot of places.

I can see how it works in a closed pipe but one thing bugs me. I can see why the pressure of the fast stream leaving a compresses fluid source is lower than teh pressurized chamber. I can also see why it goes back up as slams into the slower fluid of the wider pipe at the end.

What does not make sense to me is why teh pressure in the fast narrow tube should be lower than the ambient air pressure outside the cylinder or why it would no equalize at the speed of sound if it was.

I am left with the notion that we are still misapplying the principles and that this may have something to do with the momentum of the air and its tendency to travel in straight lines.

[villekarhunen]

Hi! Can I use part of your vid to my physic school project?

[Observer]

P.S. Bernoulli always blows.!.
In the mid 1700s Euler figured out that fluids must follow Newton's Laws and that a Pressure Gradient causes fluid Acceleration.

[joaquinflores]

I don't understand how there is higher pressure in the larger tubes than the narrower tube.

[gospelrwanda]

The pressure reduction is due to the expanding exit and not the narrow part of the system. The width of the entry may not be important but the exit, the wide exit creates a sudden increased volume hence the reduced pressure. I would like to see the same experiment be done without the expanding exit and see if there will be any differences