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Re: Derive energy from angular KE of earth?



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 get how
rotational momentum is conserved. I realize that when I fully understand
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. KE of a
rotating body is KE = 1/2 (rotational inertia) (rotational velocity)^2. I
presume that the actual shape of the earth doesn't change, so its
rotational inertia remains constant. That means that rotational velocity
must decrease.

On the other hand rotational momentum = rotational inertia x rotational
velocity . If rotational inertia stays the same and rotational velocity
decreases, then rotational momentum must get smaller. If rotational
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!