Re: [Phys-L] ?conservation of _internal_ energy

[Richard Tarara <rtarara@saintmarys.edu>]

Although my last formal thermo course was almost 50 years ago, it seems 
to me that at the heart of the 'debate' (if there really is one) is how 
internal energy is defined and what the system under consideration 
actually is. Using a vernacular definition of internal and the concept 
of absolute conservation of energy, I might want to say that the 
internal energy of the UNIVERSE is conserved.  But doing this makes ALL 
forms of energy internal--at least to the universe as a whole--and that 
certainly is not the definition of 'internal energy' that has been 
presented.  What (little) I can draw from the current conversation is 
that there seems that the definition of 'internal energy' is not quite 
universal and the boundaries of the system are also somewhat arbitrary.  
If both of these are well defined, then the conclusions of JD, DB, and 
others seem pretty straightforward.

BTW--was sent this!

"emeritus: that has become unfit for service, worn out, extinguished...; 
applied by Ovid to horses, by modern universities to retired professors"

rwt

On 1/14/2016 10:23 AM, Herbert Schulz wrote:
> > On Jan 14, 2016, at 8:57 AM, John Denker <jsd@av8n.com> wrote:
> >
> >
> > Therefore it may be helpful to look at a non-gravitational
> > example.  Consider the situation shown here:
> >   https://www.av8n.com/physics/img48/internal-energy-noncon.png
> Howdy,
>
> Yes, imagine a gas instead of the spring. As the gas expands it pushes the piston and does work. The Temperature of the gas will go down and the Internal energy of the gas will go down. So yes, the Internal energy is not constant. What is your argument that the Internal energy SHOULD be constant?
>
> Good Luck,
>
> Herb Schulz
> (herbs at wideopenwest dot com)
>
>
>
>
>
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--
Richard Tarara
Professor Emeritus
Saint Mary's College

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