Darren New <dne### [at] sanrrcom> wrote:
> Angular momentum consists of both velocity and distance. When the skater 
> pulls her arms in and speeds up, the muscular energy turns into kinetic 
> energy, but the angular momentum stays the same. When the spinning disk 
> rubs against the disk spinning the other way, the kinetic energy of the 
> disks is turned into the kinetic energy of the individual atoms (i.e., 
> heat), but the positive-signed spinning of the top disk cancels the 
> negative-signed spinning of the bottom disk.

  If we express that in overly simple terms: If a rotating system consists
of several parts, bringing those parts closer together requires energy.
If those parts are later pulled apart, that energy is released?

  Or perhaps in another way: Bringing more variation to local spinning
at different parts of the system requires energy, but evening out the
local variations and bringing the whole system to a more even state
(with less local variations in spin) releases that energy?
  (In other words, in a closed system getting two discs to rotate
independently in the same direction requires energy. Colliding those
discs so that they will start rotating as one single object will release
that energy?)

-- 
                                                          - Warp

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