Re: World's noise

[Muhsin Ogretme <ogretmem@BOUN.EDU.TR>]

As you said John, they have a preconception that rotating objects create
a sound. And also as John Denker summarized,

 -- Contact while in relative motion generates noise.  This applies to
household object but not planets (not usually, not primarily or directly).
 -- Solar heating of the bottom of the atmosphere generates instabilities
that make wind, which in turn makes noise.  Rotation changes the details,
but the main instability would be there even without rotation.  There is
every reason to believe that the sun, not the rotation, is the primary
causative factor.


Actually if i can convince the student(s) that sound requires a medium
(air e.g.) to exist along with the fact that friction can create sound,
then they can see why the earth doesn't make any noise just because it
rotates... Thank you for the ideas.

John Clement wrote:

> This is an excellent teaching opportunity.  I think the student has observed
> objects that rotate and notice that there is a noise associated with the
> rotation.  Perhaps you could bring in several objects that rotate and ask
> when they make noise, and when they make none.  Bring in a rotary grater,
> toy cars with wheels, and something that has very little friction, so the
> noise is extremely small.  Get the students to see if they can come up with
> an idea of when they make noise.  Try to guide them, and not tell them.
> Once they realize that friction or resistance to rotating is small when the
> noise is small, you can ask why you can not hear the noise of the Earth
> turning.  They should be able to say the friction (or some such words) is
> small.
> Once they come to this realization, show them an electric fan, and ask why
> it makes the shhhh ing noise.  They should realize that it is the air being
> pushed.  You might also have to use a simple Chinese fan also.  At that
> point they might be able to say, that the Earth is turning in space where
> there is no air.  The fact that space has no (or essentially no) air is an
> idea that many students do not understand.  Similarly they will tell you
> there is air on the Moon and/or there is no gravity on the moon.
>
> John M. Clement
> Houston, TX