Today, a thought about conservation and the
environment. 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.
Years ago I taught amongst
the undulating hills of Eastern Washington. You had
a keen sense of the order of nature in that lovely
landscape of dry wheat farming. One day I had an
odd conversation with a student there. He told me
he was a conservative.
When I pressed him on his politics, he looked at me
puzzled. "I thought a conservative was someone who
doesn't believe in waste," he said, "someone who
wants to preserve resources." Maybe it was living
that close to nature that shaped his definition of
conservative. Maybe, too, it had to do with the
fact I was teaching him the conservation laws of
physics in the classroom.
When we study the movement of objects, the flow of
fluids, or the transmission of heat, we face a
peculiar tension between quantities that are
conserved and quantities that are not. Students
always have an easier time with the ones that are
conserved.
Conservation of mass is easy. We tell children,
"You can't get more out than you put in."
Conservation of energy is subtler, but still
understandable. The roller coaster at the top of
the trestle has a lot of static gravitational
energy. When it gets to the bottom, that energy is
changed into 60-mile-an-hour motion -- kinetic
energy. Energy passes back and forth. It isn't
destroyed.
Momentum is a still subtler conserved quantity. If
steel and wooden marbles collide, the motion of the
steel marble is hardly altered because it has much
greater momentum.
But other quantities aren't conserved. That roller
coaster eventually degrades the gravitational
energy it had at the top, and it coasts to a halt
at the bottom. The energy isn't lost, it's just
converted to a less interesting form. It's
dissipated as heat -- disordered, messed up. We
need an engine to haul the car to the top again. We
have to supply new orderly energy.
So we create a measure of disorder called entropy.
Entropy is not conserved. Order gives way to
disorder, and entropy constantly increases. That
roller-coaster, like nature itself, poised on one
orderly perch or another -- is always about to
hurtle downhill. Nature finds its brief small
pockets or order -- then moves on to some new
chaos. And I'm back to that bright student for whom
a conservative was someone who preserved the order
of things.
One kind of conservative hopes to stay up there
without hurtling into space -- hopes to preserve
order as well as energy. Some environmentalists
want to be conservative that way. They want to hold
onto the order of nature when that order is always
transitory. Only nature's shifting energy stays
constant.
All life is tension between that which can be
conserved and that which cannot. Good engineers try
to know the difference, but so does any good
citizen. And so, for that matter, does any good
conservative.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
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