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[Phys-L] Re: Momentum Agina



| 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.

That is also my interpretation (except for the missing (1/2) factor). My
point is that in a totally inelastic collision this very KE can be
transformed into internal "spin" KE; ie, a KE which would be non-zero in the
system CM frame.

Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
http://www.winbeam.com/~trebor/
trebor@winbeam.com
----- Original Message -----
From: "John Denker" <jsd@AV8N.COM>
To: <PHYS-L@LISTS.NAU.EDU>
Sent: Thursday, December 08, 2005 4:31 PM
Subject: Re: Momentum Agina


| 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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