[geocentrism] Re: More combined post responses

Dr. Neville Jones wrote:
 > Mike wrote,
 >
 > "The law of conservation of angular momentum applies to everything in
 > any closed system. Remember that momentum (angular or rectilinear) is
 > proportional to mas and velocity. If you impart a certain momentum on
 > a molecule of a fluid it has very little mass and will have a
 > correspondingly high velocity. If that molecule is part of a rigid
 > body then the mass of the object moved is much greater and the
 > velocity therefore much less. In both cases the momentum is the same.
 > ,,, The single molecule is just a very small rigid body ..."
 >
 > No. The law of the conservation of angular momentum applies to rigid
 > bodies. You cannot circumvent this by claiming that a molecule is a
 > rigid body and therefore a liquid or gaseous collection of molecules
 > is also a rigid body. That is not what angular momentum is all about.

I never said that a fluid is a rigid body, I said a fluid was a 
collection of rigid bodies whose mechanics are approximated by fluid 
dynamics.  In principle you could use rigid body dynamics for a fluid so 
long as you treated every molecule as a seperate rigid body.  Just 
becuase this is unfeasible doesn't mean that the conservation of angular 
momentum doesn't apply when dealing with that many rigid bodies.

 > Furthermore, you keep referring to a "closed system," as if the World
 > and its atmosphere were somehow encapsulated in something. In the
 > real universe, there is no such thing as a vacuum. Hence space is not
 > a vacuum either. There exists electromagnetic radiation, debris,
 > gravity, ...

I thought we had agreed to try to agree on what happens in idealized 
situations first.  You keep trying to equate a loss energy with a 
proportional loss of angular momentum.  We can talk about that without 
considering all the complicating factors that affect the earths speed of 
rotation.

 > Angular and linear momentum might depend on mass and velocity, but so
 > too does kinetic energy. The law of the conservation of energy states
 > that energy can neither be created nor destroyed and the "closed
 > system" that that refers to is the entire physical universe.

True so far.

 > Hence,
 > the interaction of a rotating World with an atmosphere is always
 > going to be a case of losing angular momentum (i.e., angular
 > velocity, since the mass of the World does not change) to the
 > atmosphere, because of friction.

Nope.  You're equating angular momentum with energy again.

Do you agree that a completely rigid body rotating in a vacuum will 
continue to spin forever?

If so, do you agree that two rigid bodies spinning relative to each 
other in friction will both gradually change their relative angular 
velocity until they are equal while disapating the energy of the 
difference in their kinetic energy as heat while preserving their 
angular momentum?

I had a more elaborate idealized example but there really is no point 
going any further until we can agree on this point above.

Regards,
Mike.

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