Engines of Our Ingenuity

No. 1172:
CONSERVATION

by John H. Lienhard

Click here for audio of Episode 1172.

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.

(Theme music)


The Engines of Our Ingenuity is Copyright © 1988-1997 by John H. Lienhard.

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