Today, you can help me teach thermodynamics. The
University of Houston's College of Engineering
presents this series about the machines that make
our civilization run, and the people whose
ingenuity created them.
Today, the semester begins.
I teach thermodynamics to a new class. That can be
fairly arcane. I'll practice by giving you the
whole course in three minutes.
Every time anything happens -- anything at all --
both energy and matter are changed. Electricity
turns into thermal energy in your stove coils. They
glow red hot. That energy flows as heat into your
tea kettle. It transforms water into steam.
Every time anything happens -- anything at all. I
inhale. My lungs are cooled. I burn the air. I am
fueled and empowered. I pull the shade. Solar
radiation floods the room. The air expands. My skin
warms. My blood burns less oxygen. I'm changed.
Everything that happens has to obey two rules. One
is that all that energy constantly changes, but its
sum in the universe stays the same. Cool the sun
and you warm the earth. Warm an ice cube and cool
lemonade. A leaf falls. Its tiny potential energy
dissipates in air friction and in a delicate impact
with the earth. Earth and air are warmed -- too
little to notice.
The second rule is harder. It's asymetrical. It
says those changes have direction. Energy will
never flow back out of the water to recreate
electricity.
Now the plot thickens. Suppose it's your birthday
and you get a telegram. You open it. If it says,
"Congratulations!" that's nice, but no surprise.
But if it says, "Your father has fallen ill,"
that's information.
Enter a cool room and find a glowing white hot
poker in it. That's interesting. Wait an hour. The
room is warm and the poker is at room temperature.
That's not interesting at all. So we create a
measure of lack-of-surprise. We call it entropy.
Unopened telegrams and white hot pokers have low
entropy.
Energy will never flow from the room to heat the
poker back up. That telegram can never be unread.
It cannot surprise you a second time. In either
case the entropy is now very high.
Now I enter the classroom again. I go to dress
these simple ideas in their full mathematical
regalia. The students will follow the math and trip
on the ideas. They always do.
How can I tell them that their lives are so
constrained? How can I make them see any glint of
hope behind these limitations? They cannot create
energy that wasn't already there. They will, one
day, maximize their own entropy and rejoin the
earth.
How can I make them see that we would not want
things otherwise? How can I make them know that
life is a glorious game of optimizing our joy
within immutable constraints?
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
Since thermodynamics is a favorite subject of mine,
I've done many episodes that deal with aspects of the
subject. For other aspects, use the search function on this
website.
Thermodynamics rests upon a set of axioms about
nature -- physical laws. We erect mathematical
descriptions of nature upon those laws. The problem
is that it is impossible to create an axiomatic
system that is complete, coherent, and consistent.
Consequently all systems of thermodynamic laws are
ultimately flawed.
Many systems of thermodynamic laws have been
formulated. Each strives to be cleaner than the
next. In this episode I've made reference to two of
the four axioms that make up the most traditional
system. Those laws are,
First Law: Energy can be neither created nor
destroyed.
Second Law: (This can be said in many ways.
I prefer:)
The entropy of an isolated system can never
decrease.
Third Law: The entropy of any system
approaches zero as its temperature approaches
absolute zero.
Zeroth Law: (After the other three laws were
erected, people realized that a fourth principle
should precede the other three.)
Any two bodies in equilibrium with a third body
are in equilibrium with each other.
We call the Third Law into play only in certain
special systems. The Zeroth Law defines
thermodynamic equilibrium. Once that's done, it
doesn't have much other use. The first and second
laws are the ones we use heavily. One wag
paraphrased them this way:
First Law: You don't get something for
nothing.
Second Law: You can't even break even.
The Engines of Our Ingenuity is
Copyright © 1988-1997 by John H.
Lienhard.
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