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Solar System's rotation



Since the Milky Way runs roughly north south I gather the axis of
rotation of the earth and roughly the axis of rotation of the solar
system is roughly in the plane of the galactic rotation. Is that
an accident of turbulence in the formation of the galaxy or of our
system?
There's no reason to assume the plane of the orbits of other planetary
systems in the galaxy would be roughly parallel to the galactic plane of
rotation, is there?

John N. Cooper
Chemistry Department
Bucknell University
Lewisburg PA 17837
Vox 570 577 3673
Fax 570 577 1739

On Sun, 9 Sep 2001, Muhsin Ogretme wrote:

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