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Re: [Phys-L] foundations of physics: Galilean relativity, including KE



Can we agree that the total internal energy of a system is the mass of that system?

-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@www.phys-l.org] On Behalf Of John
Denker
Sent: Wednesday, September 30, 2015 11:36 AM
To: Phys-L@Phys-L.org
Subject: [Phys-L] foundations of physics: Galilean relativity, including KE

On 09/29/2015 12:52 PM, Jeffrey Schnick wrote:
In interactions, what matters is the kinetic energy of the system in
the reference frame in which the center of mass is at rest.

CUT
You can, if you wish, introduce a concept of "KE relative to the center of
mass" for some specified system. Call it the "proper internal KE" if you wish.
All observers will agree as to its numerical value. However, to call it
*"the"* kinetic energy would be an astonishing abuse of the terminology. If
you want to be understood, don't go there. In physics, there is a well-
established notion of "the" KE, and that ain't it.

Forsooth, there is a nifty theorem that says the overall kinetic energy can be
decomposed into the internal KE (relative to the center of mass) /plus/ the
macroscopic KE of the CM itself (relative to some chosen reference frame).

Homework: Formulate a precise statement of this idea, then prove it.
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