>  So you are effectively saying that regardless of heat produced by
> friction, angular momentum is always conserved.

Yes.

> This would effectively
> make a spinning object an infinite source of energy.

Why infinite?  You slow it down until it stops, then how do you propose to 
get out any more energy?

Note that this has nothing to do with angular momentum, as the angular 
momentum of something else must have been increased the exact same amount as 
the momentum of the spinning object was reduced.

Imagine a spinning ball in space, if you grabbed it in your hand (thus 
stopping it spinning and creating some friction heat) then the overall 
momentum would remain constant - ie you'd start spinning a bit.  No momentum 
has been lost, that is impossible without any external force (which you 
don't have if you're both floating in space).  Some of the rotational energy 
has been converted to heat though.  Do the sums, rotational energy is 
1/2*I*w^2 (I is moment of inertia, w is angular velocity in radians per 
second), and angular momentum is I*w.  You will see that during the 
"collision", the energy is reduced even though the momentum remains 
constant.

>  Two objects with no angular momentum at all collide off-center, and
> they get stuck to each other. The resulting union of masses will start
> spinning because of the collision.

A very good example of conservation of angular momentum...  You do realise 
that two objects travelling in a straight line "off-center" have non-zero 
angular momentum as a system?

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