"Richard Casady" wrote in message
...
On Wed, 17 Oct 2007 11:34:16 -0600, "Bill" wrote:

The source of the field rotates with the earth. The field itself is
decoupled from the source once it leaves the source.

Sorry, but you are the only one who thinks that the earths magnetic
field doesn;t rotate with it.

Mason Peck of Cornell University in Ithaca, New York, US, has received
a grant to study the idea, which is based on the fact that magnetic
fields exert forces on electrically charged objects.
He says a satellite could charge itself up in one of two ways - either
by firing a beam of charged particles into space, or simply by
allowing a radioactive isotope to emit charged particles. The charged
satellite would then be gently pushed by Earth's rotating magnetic
field, enabling it to change orbit and even escape to interplanetary
space

Took all of two minutes with a search engine and 'earths rotating
magnetic field'. Got quite a few hits for something that doesn't
exist.

Casady

http://en.wikipedia.org/wiki/Faraday_paradox

"The experiment proceeds in three steps. First, the magnet is held to
prevent it from rotating, while the disc is spun on its axis. The result is
that the galvanometer registers a direct current. The apparatus therefore
acts as a generator, variously called the Faraday generator, the Faraday
disc, or the homopolar (or unipolar) generator.

In the second step, the disc is held stationary while the magnet is spun on
its axis. The result is that the galvanometer registers no current.

In the third step, the disc and magnet are spun together. The galvanometer
registers a current, as it did in step 1."



Another reference:

http://www.physics.brown.edu/physics...emo/5k1080.htm

a.. "Rotating disc; rotating magnet
As stated above, the motion of the magnetic disc is immaterial. Therefore,
as long as the conducting disc is rotating, the galvanometer will indicate a
current as in the first case. "


Case 1: The conductor rotates but not the magnet and voltage is measured.

Case 2: The magnet rotates but the conductor remains stationary. No voltage
measured.

Case 3: The magnet and conductor rotate together and voltage is measured.

Premise: A conductor must have relative motion through a magnetic field to
produce voltage.

Conclusions:

Case 1: Relative motion between conductor and magnetic field.

Case 2: No relative motion between conductor and magnetic field, yet
relative motion between magnet and conductor. Voltage is not measured.
Simplest explanation: Magnetic field does not rotate with magnet.

Case 3: No relative motion between magnet and conductor, yet voltage is
measured. There must be relative motion between magnetic field and
conductor. Simplest explanation (also consistent with #2): magnetic field
remains fixed in space regardless of rotation of magnet.

If you can offer a better explanation of Farady's Paradox let's hear it.

A better way to say it is that the earths magnetic field is decoupled from
its source as it rotates.

Also I'm not the only one who thinks so:

http://www.geocities.com/terella1/

And our very own NASA:

http://www-spof.gsfc.nasa.gov/Education/magnQ&A3.htm

1.. Can we tell if a symmetric magnetic field rotates around its axis?
a.. (shortened)
Question that puzzles me for a long time is basically very simple. Does
earth's magnetic field rotate around it's magnetic poles axis Well, looking
at the rotation of magnetic anomalies, and rotation of magnetic poles, this
is true. But that cannot be, and should not be considered as rotation of
magnetic field on it's magnetic axis. The experiments can show us that the
rotation of any magnetic field on it's magnetic axis is impossible and
contrary to the very laws of nature. That should be viable even for complex
magnetic structures as earth's magnetic field is. Yet, it is obvious that
majority of scientific community is even unaware of Faraday's experiments
with rotating magnets.. REPLY


Your question brings up something which has confused many people (even me,
when I was younger).


Basically, the rotation of axially symmetric magnetic fields in a vacuum
around their axis of symmetry is NOT observable. If you have a bar magnet
and attach it to a shaft which rotates it around its symmetry axis (the line
connecting its poles) you will not find any difference whether it rotates or
not. The outside magnetic field--and the electric field, too--is not changed
by the rotation, and the equations which determine these fields do not
reflect rotation of the source.



However, that is in a vacuum (and to all practical purposes, also in
air). When matter is present--especially, electrically conducting
matter--rotation may make a difference. Take for instance Faraday's disk
dynamo, where a conducting disk rotates in a magnetic field (see
illustration in http://www.phy6.org/earthmag/dynamos.htm ). The magnetic
field may be axially symmetric, and the disk and its motion have the same
symmetry, but it makes a difference, because a moving CONDUCTOR in a
magnetic field B, at a point moving with velocity V, experiences an electric
field E = VB in a direction perpendicular to both B and V (mathematically
you need use here a "vector product", but let me not go into that detail).

If instead the magnet rotates around its axis and the disk is at rest,
nothing happens to the disk, which shows that it is the motion of the
CONDUCTOR that matters, not that of the magnetic source. Except of course in
non-symmetric sources, where the motion causes observable changes in
B--these do matter, and such irregular components clearly rotate with the
Earth.
If the disk is not connected, the only effect of this E is to move
electric charges across the disk, until they create an opposite field which
cancels E, and nothing more happens. However, if electrical contacts from
the outside touch the disk as in the drawing, connecting it to a circuit
which does NOT rotate, then the electrical charges which try to neutralize E
are carried away to the outer circuit, and the device works as an electric
generator.
Just for your interest: at one time it was suggested that any spinning
matter, conducting or not, produced a magnetic field, but experiments showed
that was untrue. See 2nd paragraph in section 14 on web page
http://www.phy6.org/earthmag/ /mill_5.htm.