Re: Derive energy from angular KE of earth?

[Mark Sylvester <msylvest@XNET.IT>]

Brian, we agree that the KE of the system decreases, but for the angular
momentum to decrease we must find an external torque or else show how the
mass distribution changes to produce a change in the moment of inertia so
that the angular momentum does not change. (Take a look at Leigh Palmer's
gedankenapparat (unfortunately described under the subject line "phys-l
digest")). About the axis of the generator, you first bring the generator
rotor + gyroscope to rest (seen from a non-rotating frame), and use the
gyroscope flywheel spinning about a perpendicular axis to keep it there
while the earth continues to spin. Note that you will have exchanged ang.
mom. between earth and rotor in the process. Now when you use the generator
to do work there is an electromagnetic torque between the rotor and the
earth - angular momentum is again exchanged between these parts of the
system. This is not the answer, however, since we can go on doing work with
the generator for as long as we want, it seems to me. I note that there
must also be a precession caused about the third perpendicular axis when
you do work with the generator, but this only seems to complicate matters
as far as ang. mom. conservation is concerned. Mark

At 23:01 23/12/03 -0600, Brian Whatcott wrote:
> Perhaps I am not fully conscious of the effect you're pondering.
> I am supposing that you spin up a flywheel, providing complementary m=
> omenta,
> then extracting momentum from the disk, with the identical reduction
> to the complementary agency?
>
> Perhaps you are considering the case of generating energy without
> losing momentum.   A perpetual motion, kinda?
>
> Brian W
>
> At 08:34 PM 12/23/2003, you wrote:
> >Well, it is true that spinning up the flywheel will transfer angular
> >momentum to the earth, but after that, if the bearings are really go=
> od,
> >there will be a very small amount of angular momentum transferred be=
> tween
> >the wheel and the earth.
> >
> >Fred Bucheit
> >
> > >From: Brian Whatcott <betwys1@SBCGLOBAL.NET>
> > >
> > >How about treating the angular momentum as a storage method.
> > >Spin up a flywheel, and the Earth takes up a complementary
> > >   momentum (if you must...)
> > >
> > >Brian
> > >
> > >At 10:01 PM 12/22/2003, you wrote:
> > > >[This was brought up on PHYSHARE-L as well, and I still don't ge=
> t how
> > > >rotational momentum is conserved. I realize that when I fully un=
> derstand
> > > >it, I am going to feel like an idiot, but here goes....]
> > > >
> > > >If the energy that is used to light the bulbs, etc., comes from =
> the
> > > >earth's rotation, then the earth needs to lose kinetic energy. K=
> E of a
> > > >rotating body is KE =3D 1/2 (rotational inertia) (rotational vel=
> ocity)^2. I
> > > >presume that the actual shape of the earth doesn't change, so it=
> s
> > > >rotational inertia remains constant. That means that rotational =
> velocity
> > > >must decrease.
> > > >
> > > >On the other hand rotational  momentum =3D rotational inertia x =
> rotational
> > > >velocity . If rotational inertia stays the same and rotational v=
> elocity
> > > >decreases, then rotational momentum must get smaller. If rotatio=
> nal
> > > >momentum of the earth gets smaller, then the L of something else=
>  must get
> > > >larger.
> > > >
> > > >So, the rotational momentum of what gets larger?
> > > >
> > > >Marc "Zeke" Kossover
> > > >The Hockaday School
> > >
> > >
> > >Brian Whatcott    Altus OK    Eureka!
> >
> >_________________________________________________________________
> >Have fun customizing MSN Messenger =97 learn how here!
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>
> Brian Whatcott    Altus OK    Eureka!=20