Re: [Phys-l] Bernoulli, Coanda, or Lanchester-Prandtl

[John Denker <jsd@av8n.com>]

On 09/01/2011 06:36 AM, chuck britton wrote:
> This 'Back of spoon pulled into stream of water' is a very poor 
> (perhaps wrong?) illustration of the Coanda Effect

Agreed.  The spoon effect has got nothing to do with Coanda.

>  since the 
> 'Entrained Fluid' would be air which doesn't provide enough reaction 
> force. 

That argument is correct and sufficient to prove the point.

Also by looking at the water downstream you can see that there's
no entrained air.

> Surface tension is a better explanation of this observed 
> effect (IMHO).

Also correct.  I've done some experiments.

One easy experiment is to measure the magnitude of the spoon
effect as a function of the velocity of the water stream.  It
doesn't scale the way the Coanda effect would scale.

One can go further and say that the spoon effect has got nothing
to do with the mechanism by which wings produce lift (which has
also got virtually nothing to do with the Coanda effect).  So
explaining lift in terms of Coanda as illustrated by the spoon
is completely wrong twice over.

============================

Whatever happened to the idea of "check your work"?

Isn't that supposed to be taught in 2nd grade and every grade
thereafter?

Feynman said that if you want to be a scientist, "The first 
principle is that you must not fool yourself -- and you are
the easiest person to fool."
  http://www.lhup.edu/~DSIMANEK/cargocul.htm

Science is a collection of procedures for finding the right
answers and avoiding mistakes.  The first principle for
preventing mistakes is to realize that mistakes are possible.
So check your work!

These guys who publish articles explaining lift in terms of
Coanda as illustrated by the spoon ... did they think about it
even for a femtosecond?  Did they even /consider/ the possibility
that they might be making a mistake?