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Re: [Phys-l] air pressure question

You might also look up the paper by Tonon, Nakiboglu, Gollard, and Hirshberg in the proceedings of the 20th International Symposium on Music Acoustics 25-31 August 2010, Sydney and Katoomba, Australia. They get the opposite sign for the pressure differential caused by the centrifugal effect and make a convincing argument that the pressure at the moving end is atmospheric pressure and the pressure at the non moving end is Patm - 1/2*rho*omega^2*L^2, where L is the length of the tube. They use the Strouhal Number to eventually argue that the fundamental will usually not be heard. In their analysis, the speed of the air through the pipe is given by U=omega*L (a rather simple result).

There is a lot of physics in this paper and I think it deserves a read. it's not just phenomenological like most of the papers on the subject.

Bob at PC


-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
bounces@carnot.physics.buffalo.edu] On Behalf Of John Mallinckrodt
Sent: Monday, January 24, 2011 4:16 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] air pressure question

You might Google on "corruga horn" or see the excellent article by
Frank Crawford, F. S. Crawford, ÔÔSinging corrugated pipes,ÕÕ Am. J.
Phys. 42, 278Ð288 (1974).

John Mallinckrodt
Cal Poly Pomona?

On Jan 24, 2011, at 1:09 PM, William Robertson wrote:

I'm sure people are familiar with corrugated plastic tubes that make
different sounds when you twirl them. You can hold one end above
small
bits of paper on a table and twirl the opposite end. The bits of
paper
rise up into the tube. My explanation is that by twirling the free
end, you are accelerating the tube away from the air inside (lab
frame
of reference) or there's a centrifugal force pushing the air out
(rotating frame of reference). That creates a low pressure area at
that end, which would force air up into the tube. [I used to explain
this as a Bernoulli effect, but given the discussion a while back, I
am convinced that is incorrect] First, is my explanation correct?
Second, what causes the paper on the table to rise up into the tube?
Is it just the air being pushed into the tube dragging the paper
along
with it?

Bill



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