[Phys-L] Re: Momentum Agina

[John Denker <jsd@AV8N.COM>]

Bob Sciamanda wrote:

>  The objects can stick together and have the KE transferred to internal
> degrees of freedom (contribution a), such as a spinning part.  Your assumed
> constraint is not necessarily so - neither is it required for the pursuit of
> your conclusion, which is still valid.

Well, this gets into the quagmire of deciding what we mean by "the"
kinetic energy.  There are, in principle, an infinite number of
different KEs, depending on length-scale.
   http://www.av8n.com/physics/kinetic-energy.htm

In HS physics, when somebody asks for "the" KE of an object, we usually
take it for granted that the microscopic KE associated with thermal energy
is not included.

My interpretation of the original question was that "the" KE of each of
the two original objects was just m v^2, where m is the mass of the object
and v is its macroscopic velocity.  This is not the only possible
interpretation, but it is well within the HS physics mainstream.

Whether you want to include rotational KE of little sub-parts of
the objects is something of a judgement call, but I'm pretty sure
it would  be outside the spirit of the original question.  Also, in
the rail-car scenario I presented, I expressly limited the analysis
to the one-dimensional case.  I think the D=1 case suffices to
elucidate the fundamental conceptual points.
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