Re: dW turns into dQ

[Bob Sciamanda <trebor@VELOCITY.NET>]

Joel Rauber wrote:
> You have made your point clearer; I'm not sure where the differences
lie,
> but there are some, perhaps they are mostly philosophical.
> . . .

Hi Joel,

I think that we two are very close in our thinking.  Let me spin a little.
In the (very common) case of a current carrying resistor immersed in a
fluid, some would choose to exclude the resistor from the defined system
and then call the energy transfer into the system dQ (Heat);  others would
include the resistor in the defined system and call the energy transfer dW
(work). Still others might say other things;  but all would agree in any
practical application.

I would say that this fits your term a "philosophical difference".  In a
practical application of the physics (as in the design of an electric
coffee pot) such considerations never become conscious  -  the engineer
will calculate the energy input  in terms of the energy spent by the EMF
which "drives" the current through the resistor (Eit).

Note that even the one who would exclude the resistor, and so call the
energy transfer dQ,  would in practice not measure this dQ at the defined
system's boundary, but far removed therefrom - at the EMF, as an
electrical quantity.

 In practice, difficulties arise only when a teacher forces a student to
choose among the "purely philosophical" interpretations.

Bob

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor