From: schinder@leprss.gsfc.nasa.gov (Paul J. Schinder)
Subject: Re: Thermodynamics FAQ
Reply-To: schinder@leprss.gsfc.nasa.gov
Organization: Goddard Space Flight Center
Date: Fri, 24 Jul 1992 17:45:59 GMT

In <henley.920724101706@wilbur.eng.auburn.edu> henley@eng.auburn.edu (James Paul Henley) writes:

>In article <schinder.711942290@leprss.gsfc.nasa.gov> schinder@leprss.gsfc.nasa.gov writes:
>>
>>Foolish mysticism, completely unlike "the uncertainty principle".
>>Energy is definitely measurable.  (*Define* the term "pure energy").

>I didn't say energy wasn't measurable,  I said that you have to use matter
>to measure it.

In one sense, this is a tautology, since we're made of matter and we
do the measuring.  This also depends on what you mean by measuring,
but that can turn into a can of worms.  You define for me what you
mean by "pure energy" (Are photons "pure energy"?  If so I can
"measure" them with other photons.  If photons are, why aren't W or Z
bosons?  Are neutrinos "pure energy"?).

>>High energy experimentalists spend their lives measuring it.  There's
>>no real distinction between matter and energy; one can be converted
>>into the other.

>OK, I'll bite, how do you measure pure energy apart from matter without
>allowing it to interact with matter?
>Give me the measurement technique, and a reference, if you please.

First I need a definition of what you mean by "pure energy".  I have no
idea what you mean.  Energy isn't mystical.

>>However, you're neglecting the incoming vs. outgoing radiation.  In
>>this respect, the earth is *not* (and can't be so long as the sun
>>shines and the earth radiates) a closed system.  In any sense.  No
>>doubt (for obvious reasons) you want to try to ignore this "energy",
>>but that's too bad.  Thermodyanics has no problems with it.

>You are confusing closed systems with isolated systems.  You didn't read
>the FAQ.  The definition of a closed system is a system that does not have
>mass transfer across system boundaries.  Maybe it is because of the balloon
>model?  The wall of the kind of balloon I have in mind does allow a lot of
>radiation to enter the balloon.  They reflect some of it too.  In fact they
>are selective in which radiation they allow to enter, and which they reflect.
>I'll be generous and say that maybe you thought I meant one of those foil
>balloons.  They definitely reflect a large amount of radiation.  In that 
>case it would *not* be a good model.  I'm talking about the old fashioned
>toy kind made out of latex.  (or synthetic latex)

Although I did read the FAQ, the definition used there is not the
definition used in physics (closed == isolated == sealed off from the
rest of the universe), and I just slipped back into the definition I'm
used to.  Sorry.

>Are you are trying to say that the earth is not a closed system because some
>sunlight gets converted into matter, thus increasing the mass of the earth?

No, that's not significant.


>>>What about the order of the snowflake?  A snowflake indeed appears to have
>>>a high degree of order, but remember, we are talking about ordered energy.
>>
>>We're talking about ordered water molecules.  Not energy.

>I thought we were talking about thermodynamics.  Go back and read the
>definition of thermodynamics.  Molecules depend heavily on energy to
>even stay together.  Molecular bonds ring a bell?  Bonding *energy*?
>Latent heat?

Physicists don't usually make the artificial distinctions you're
trying to make here.  When computing the change in entropy, *all*
energy flow across the (artificial) boundary of the system is
significant, so it doesn't really matter whether how it enters or
leaves.

>>Paul J. Schinder
>>NASA Goddard Space Flight Center
>>schinder@leprss.gsfc.nasa.gov

>James P. Henley Jr.
>Chemical Engineering Dept.
>Auburn University

--
--------
Paul J. Schinder
NASA Goddard Space Flight Center
schinder@leprss.gsfc.nasa.gov