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-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@www.phys-l.org] On Behalf Of John
Denker
Sent: Wednesday, September 30, 2015 4:36 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] foundations of physics: Galilean relativity, including KE
On 09/30/2015 12:48 PM, Jeffrey Schnick wrote:
Can we agree that the total internal energy of a system is the mass of
that system?
I agree with the intended meaning, I agree with the physics idea ... but the
terminology is tricky.
It might be safer to say the /rest energy/ is equal to the mass of the system,
in the appropriate units.
That's pretty much a direct translation of Einstein's equation into words.
E_0 = m c^2
I suggest calling the LHS the /rest energy/ because thermodynamics books
have various definitions of "internal energy" that you probably wouldn't be
very happy with.
Also I suggest writing Einstein's equation with a subscript zero on the E, to
remind people it's just one piece of the energy.
The idea of /rest/ energy refers to the CM of the system being at rest. If you
have a spinning flywheel, or thermal phonons in a solid, the KE of the
excitations /relative to the CM/ is part of the system's rest energy and
contributes to the mass of the system.
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