Re: pinhole helium

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From: Rilla Chaney (rmchaney@comcast.net)
Date: Fri Jan 16 2004 - 15:33:47 PST 

Message-ID: <400874DB.CF1AF9D8@comcast.net>
Date: Fri, 16 Jan 2004 15:33:47 -0800
From: Rilla Chaney <rmchaney@comcast.net>
Subject: Re: pinhole helium

Is there a helium molecule?

Rilla

Paul Doherty wrote:

> Hi Irene
>
> Helium molecules are less massive than nitrogen and so the speed of sound
> in helium is faster than the speed of sound in air. (Helium is 4 amu while
> nitrogen is 28 and the average of air is 29 amu) The speed of sound is
> proportional to the square root of the molecular mass so the speed of sound
> in helium is (29/4)^0.5 times greater than that in air = 2.7 times greater.
>
> The resonance frequency of your mouth depends on the time it takes sound to
> cross your mouth cavity. When you fill your mouth with helium the time it
> takes sound to cross your mouth (at the high sound speed in helium) is less
> than the time it takes when your mouth is full of air. By 1/2.7.
>
> The resonant frequency of your mouth goes up like the inverse of the
> crossing time, it goes up by a factor of 2.7.
>
> So your voice goes up by more than an octave.
>
> The increase in frequency has nothing to do with changing the vibration
> frequency of your vocal chords. This is a standard science urban legend.
>
> Paul d
>
> >I was wondering if anyone can give me any information on what causes your
> >voice to sound squeeky when you "talk" using the helium gas. Irene
> >Hirota
> >
>
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