Re: [Phys-l] question about Bernoulli

[Bernard Cleyet <bernardcleyet@redshift.com>]

Not drag, but push.

The thermal motion outside the cylinder near and at the hole results in diffusion into the cylinder.   The net motion of the gas inside is in the direction of the piston, so those molecules collide w/ those formerly outside resulting in a partial vacuum (relatively) at the hole, etc.

bc  waiting for JD. and thinks it's similar to the operation of a diffusion pump.



On 2010, Nov 17, , at 13:04, William Robertson wrote:

> Explanation 3--Entrainment.
>
> The basic argument here is that fast moving molecules "drag along"  
> molecules near the surface in question. So with the syringe, the  
> faster moving molecules near the sides of the syringe drag along  
> molecules closer to the sides of the syringe (there is a stationary  
> layer right next to the sides) and create an area of lower density.
> This lower density means lower pressure. What is the dragging  
> mechanism here? If we're talking about an ideal gas, can this happen?  
> And if the answer is that this doesn't apply to an ideal gas, then  
> does that mean Bernoulli doesn't apply when friction and turbulence  
> are at an absolute minimum?