From: Geoff Ruth (geoffreyruth@usa.net)
Date: Tue Nov 23 1999 - 11:44:16 PST
Message-ID: <19991123194416.26646.qmail@nwcst315.netaddress.usa.net> Date: 23 Nov 99 11:44:16 PST From: Geoff Ruth <geoffreyruth@usa.net> Subject: Re: [pinhole sound transmission]
Marc,
I like your questions to pinhole a lot. I think your sound question is great
-- have you seen the explo exhibit where you slowly evacuate the air from a
jar with a bell ringing inside, and after a certain point, you can no longer
hear the bell? If I remember correctly, you could no longer hear the bell
after the pressure was between .001 and .0001 atm. I wonder if the lower
concentration of molecules at these pressures means that the molecules don't
bump into one another as often and therefore the sound disturbance dies out
more quickly. Does this make sense?
As for your e-mails, I saw your question about sonar shadowing. I don't think
that I saw anything about acids & bases, but it's possible that I just
overlooked it.
-Geoff
> We often say that sound is not transmitted in space.
> The explanation offered is that this is because there
> are no molecules to propagate the disturbance and a
> bell jar with a ringing bell is sometimes shown to
> become silent when the air is pumped out of the jar.
> My question is, at what point does the sound cease to
> be transmitted? I know we are not establishing a
> vacuum in the jar, just lower pressure. In fact, the
> lowest pressures I have seen in a lab are on the order
> of a picotorr to a nanotorr. Even at this low
> pressure, there are many molecules per liter. My
> calculation shows there to be about 30 billion
> molecules per liter at standard temperature and one
> picotorr. So, is sound actually being scattered at
> this pressure (by random motion of molecules) rather
> than propagated? At what mean free path does the
> propagation cease? If it is being propagated but at
> too low an intensity to be measured, then wouldn't the
> same be true for outer space since there are many
> particles out there that are capable of transmitting
> sound (even if it is only one molecule per cubic
> meter)?
>
> Just wondering.
____________________________________________________________________
Get free email and a permanent address at http://www.netaddress.com/?N=1
This archive was generated by hypermail 2b29 : Thu Oct 19 2000 - 11:09:56 PDT