Re: [Phys-l] question about Bernoulli

[chuck britton <cvbritton@mac.com>]

Very nice and understandable.
(Perhaps getting a bit too close to a 'Conceptual' explanation?!?!?  ;-)  )


I've wondered about a particularly non-viscous system - Superfuild 
4He - well below the transition T.
There certainly wouldn't be any 'drag' affect involved in the lower 
pressure/higher velocity venturi sort of exp.
Anybody have exp. results to relate??

.
At 10:31 AM -0800 11/19/10, curtis osterhoudt wrote:
> Not sure how applicable this is "at the molecular level", but a heuristic (at
> least in the limit of incompressible fluids) explanation is nice, and doesn't
> rely on the mathematics, or at least on the notion of streamlines 
> and the like.
>
>    Consider a pipe of cross-sectional area A1, which connects to a section of
> smaller cross-sectional area A2. Continuity (which students can 
> understand at a
> gut-level, at least for incompressibles) says that the speed in the 
> vicinity of
> A2 must be higher than that near A1. For this to have happened, the linear
> momentum of a given fluid parcel is higher at A2 than at A1, and so 
> the pressure
> at A1 has to have been higher than at A2.
>    Reversing the flow, or simply connecting back to a pipe section of larger
> cross-section argues for a higher pressure at the larger cross-section again.