[geocentrism] Re: Angular momentum
- From: Mike <mboyd@xxxxxxxxxxxx>
- To: geocentrism@xxxxxxxxxxxxx
- Date: Wed, 20 Oct 2004 02:22:00 +0100
Dr. Neville Jones wrote:
> Group,
>
> There still seems to exist confusion as to what angular momentum is,
> and I think that the main reason for this is that "everyone just
> knows" that the acentric problem of a spinning World/atmosphere
> system (as put forward by Aristotle) has been explained away by
> invoking the law of the conservation of angular momentum.
Aristotle didn't know about Newton's first law of motion - he thought an
object in motion had to have a force to keep it in motion. Why should
he have known any better, it is not obvious when one is used to living
in an atmosphere. Do you disagree with Netwon's first law?
> We need to delve a little deeper into the physics here. Angular
> momentum is defined as the product of moment of inertia with angular
> frequency about a common axis of rotation.
For any system of particles it is defined as the sum of the products of
each particle's displacement vector from the chosen origin and the
particle's linear momentum. Any non-accelerating origin may be chosen,
and it is defined for *any* system of particles (including planets and
atmospheres). If there is no external torgue about the chosen origin
the angular momentum of the system is conserved. For a single rigid
body rotating about a symmety axis it simplifies to the description you
gave above.
> Molecules of a gas do not
> have any angular frequency about a common axis of rotation, except in
> the case of something like a hurricane or a tornado
It is defined for any system of particles, see above.
> Sometimes travelling along a straight line, with absolutely no axis
> of rotation.
A particle moving in rectilinear motion will have a non-zero angular
momentum about any origin except those that that lie on the line it is
moving along. It's implicit in the definition.
> Now, the 'conventional' treatment of our atmosphere is that these
> molecules interact with one another, such that the angular momentum
> of the whole is conserved.
And if you imagine them all to be little billiard balls bouncing off of
each other and use the actual definition of angular momentum you will
find that it is. (Billiard balls may be an ald fashioned way of
thinking about particles but it works if we're just talking about momentum)
> This is wrong for at least two reasons:
> There are thermal convection currents within the atmosphere which
> have a great effect on the air molecules. These convection currents
> have absolutely nothing to do with angular momentum
Angular momentem is well defined for *ANY* system of particles.
>(these are
> perhaps the greatest reason why Mike's so-called "closed system" is
> invalid).
I only mentioned closed systems in trying to discuss simplified models.
You are the one who keeps insisting on talking about complex phenomena
when you don't even appear to believe in or understand (I know not
which) Newton's three laws of motion (note to the pedants: usual
relativistic caveats apply). Your argument was that there is a
*necessary* loss of angular momentum due to loss of energy due to
atmospheric friction. We don't need to consider complicated systems to
show that your premise is wrong.
> They are due to the incoming heat from the Sun, heating up
> different components of the World and its atmosphere at different
> rates, depending upon composition. These convection currents will act
> so as to disrupt any alleged angular momentum of our considered
> molecule.
Prove it then. Give us the maths that shows that if the earth were
rotating and orbiting the sun then the heat from the sun would exert a
torque on the earth to slow it down - that's effectively what you're
saying. You just keep stating this with no backing. If you try to do
the maths you might see where you're thinking is wrong.
> Their effect upon our molecule will be totally
> overwhelming, compared with any possible transference of angular
> momentum.
You seem to think that total angular momentum is the total amount of
spinning going on by each particle. I urge you read up on the
conventional classical defintion of angular momentum.
> ANY 'ANGULAR MOMENTUM' THAT OUR MOLECULE MAY HAVE HAD WIL L
> BE CHANGED BY THE ACTION OF SOMETHING ORIGINATING OUTSIDE OF THE
> WORLD/ATMOSPHERE SYSTEM.
FOR ANY SYSTEM OF PARTICLES, THE TOTAL ANGULAR MOMENTUM IS CONSERVED
UNLESS THERE IS A TORQUE ABOUT THE CHOSEN ORIGIN. FRICTION WITHIN THE
SYSTEM CANNONT PROVIDE THAT TORQUE - IT WOULD BE LIKE TRYING TO PICK
YOUSELF UP BY YOUR BOOTSTRAPS.
> The second reason is closely tied to the first. As I have
> said many times now, angular momentum is an attribute of rigid
> bodies. That is how it is DEFINED. Note that ALL the particles within
> a rigid body have the SAME angular frequeny about a COMMON axis of
> rotation, irrespective of how far each of them is from that axis.
> Angular momentum does not apply to gases, nor, in general, to fluids.
Again, I urge you to learn up on some basics physics before claiming it
is inconsistent with the acentric model.
> Molecules in a gas transfer linear momentum between themselves, but
> even these are inelastic collisions.
Elastic or not, every action has an equal and opposite reaction. Are
you now saying that linear momentum isn't conserved when two particles
collide?
Regards,
Mike.
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