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Re: entropy - motivation for definition



(2) It shows (I would say by design) the direction of spontaneous
irreversible change. It is obvious thermal energy flows from the hotter
object to the colder object.
......

Let's say the surroundings are at lower T. Q leaving the system (-) is
the same as Q entering the surroundings (+).

When we enter this kind of discussion, we would like to continue the
shorthand language -- as is used above, but, in doing so, we fall into
traps because we fail to be precise:

Q does not flow -- it does not move -- it does not in fact exist. Q is
"done" -- it is an action. It is not a substance.

Although the shorthand language for "energy" is usually less dangerous, it
will often get us mired: We often mistakenly think of Q as energy -- It is
not! But even worse neither does energy flow -- it does not move -- it
does not in fact per se exist. It is a property of a system. Just as
"blue" does not per se flow, move, exist. It is a property of a system --
a property with different characteristics than energy, but they both are
properties nonetheless. As a mater of fact, energy is even more obtuse --
It is a mathematical invention.

OK OK OK you don't want to hear me say this every time these issues come
up, but......

Jim



Jim Green
mailto:JMGreen@sisna.com
http://users.sisna.com/jmgreen