Re: [Phys-L] work versus mechanical transfer of energy

[Diego Saravia <dsa@unsa.edu.ar>]

2016-01-06 22:35 GMT-03:00 John Denker <jsd@av8n.com>:

> On 01/06/2016 05:49 PM, Lulai, Paul wrote:
> > If U is internal energy, or the
> > energy if the constituents if the system, can we still think of it as
> being
> > conserved? It may or may not be constant, but energy that enters or
> leaves
> > the system can be accounted for. This internal energy would not be
> > constant, but it would be conserved.
>
> OK, good point.
>
> Just now I rewrote my screed on the subject, as follows:
>
> > > Some folks try to simplify the equation by introducing the
> > > “internal energy” U. However, to me that seems like one step
> > > forward and two steps back. For one thing, the definition of
> > > E is reasonably well known, whereas it’s hard to learn and
> > > hard to remember what’s supposed to be included in U.
> > > Secondly, in situations where the parcel moves significantly
> > > in the dh direction, if you just ignore h then energy is not
> > > conserved. You have to keep track of m g dh one way or another
> > > (either as part of the dE of the parcel, or as part of the
> > > energy flowing across the boundary). So the only remaining
> > > question is whether you will need one new variable or two
> > > (h alone versus h and U both).
I do not understand

I like the first principle in thermodynamics expresed as "there exists a U
function" (one of the zillions of forms)

Weinreich way, book Fundamental thermodynamics.







> Better?
>
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-- 
Diego Saravia
Diego.Saravia@gmail.com
NO FUNCIONA->dsa@unsa.edu.ar

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