From: pauld@exploratorium.edu
Date: Sun Feb 29 2004 - 22:50:31 PST
Message-ID: <1959.209.239.173.234.1078123831.squirrel@www.exo.net> Date: Sun, 29 Feb 2004 22:50:31 -0800 (PST) Subject: Re: pinhole sound vacuum From: pauld@exploratorium.edu
Hi Damon
I would put a ringing alarm clock with a bell in a vacuum chamber together
with a recording tape recorder (I've actually done this) It helps to
suspend the alarm clock from thin string to keep the sound from travelling
through the metal of the platform to the recorder. You could also suspend
the recorder.
Record the bell, turn on the vacuum pump, pump down the jar, turn off the
pump keeping the low pressure, near vacuum in the bell, and record the
bell again. It will be much quieter with the near vacuum.
The human ear is so good at detecting faint sopunds that you probably
cannot produce total quiet, but it's still a good demo, with an excellent
vacuum pump you could produce quiet.
Paul D
> Howdy pinhole folks,
>
> A teacher friend of mine gave me this scenario and I
> was wondering what you thought.
>
> She is teaching a 3rd grade class and they have done a
> number of activities seeing a number of materials that
> sound will travel in: air, water, wood, and others.
> However, as they are wrapping up their investigations,
> she is realizing that the part where they learn that
> sound cannot travel through a vacuum is just something
> she is telling her students. She would like to be
> able to show this.
>
> So, I know the standard demo to show this is the bell
> in a bell jar that you remove air from. I also have
> read a few critiques (including the "Physics Begins
> with an M..." book) arguing that this demo is
> demonstrating a large impedance mismatch between glass
> and the rarified air inside and does not create nearly
> the vacuum required to show sound not traveling
> through air. I have not done the experiment, but they
> argue that if you put a microphone INSIDE the bell
> jar, it can pick up the sound of the bell.
>
> So my questions:
> 1. Is there a demonstration that actually does show
> that sound cannot travel in a vacuum that could be
> done in a 3rd grade class. (We do have access to high
> school physics lab stuff.)
> 2. If there is not a good demonstration, if we did do
> the bell jar demo, what could we say about it that
> would help the third-grade students' understanding but
> was not wrong?
>
> thanks,
> damon
>
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