Engines of Our Ingenuity

No. 277:
POWER PRODUCTION

by John H. Lienhard

Click here for audio of Episode 277.

Today, I want to pit you against your machines. 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.

I ask you to do an experiment. I ask each one of you to run up several flights of stairs as fast as you can. Use your watch to measure how long it takes to do it. Say you run up three flights, and it takes you twenty seconds.

Now multiply the height of the stairs by your weight. If you weigh 150 pounds, and the three flights go up 40 feet, then you've done 6,000 foot-pounds of work in 20 seconds. That's 300 foot-pounds a second. A horsepower is 550 foot-pounds a second, so you've generated just over half a horsepower.

If you're in good shape, you can generate a whole horsepower in a short burst like that. But what if you climb all day? Can you climb a 6000-foot mountain in 8 hours? That's only about thirty foot-pounds a second -- about a twentieth of a horsepower.

This gets interesting when you compare your power with the machines that serve you. Suppose human beings had to power the generator that supplied a 150-watt light bulb. It would take 15 people doing five-man eight-hour shifts to keep that light burning. An automobile engine that generates 100 horsepower does the work of 2000 people. But when those people have to rest at the end of eight hours, the automobile keeps right on going. If everyone in America worked like a galley slave, they'd generate barely enough electricity to power a small city.

The engines of our ingenuity are big and powerful, and we're no match for them. We've become absolutely dependent on huge supplies of power. But the very magnitude of our power plants threatens our well-being. If they burn fossil fuel, they don't just spoil the air around the plant, they endanger the whole planet. If they use nuclear fuel, we can't figure out what to do with their waste. Solar collectors, in any form, eat up huge amounts of real estate.

So try my experiment -- time yourself running up the stairs. You'll see what an astonishing difference in scale we've created between our machines and ourselves. We're like mice directing the movements of elephants. Too many of our machines can crush us with a wrong step. The difference in scale is increasing. And the greater it is, the more dangerous our machines become.

In the end, our only protection from those great beasts is restraint -- restraint in the use of energy -- restraint in our wants -- restraint in the use of our ingenuity. Run up the stairs and measure your power output. Take a long close look at the enormous gulf between us and our machines. Learn how to view those machines with a well-balanced mixture of fear and respect.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)


                                                          
             (your weight in lbs) x (the height in feet you lift yourself)
Horsepower = __________________________________________________________
                    (550) x (the time in seconds that it takes you)

Power in Watts = (746) x (power in Horsepower)

   Power Supply                         Power Output, HP
  ______________________________________________________
   A laborer working all day                      0.05

The cyclist who spent 4 hours flying 
     the human-powered airplane, 
                 Daedalus, 74 miles               0.25

   A farm horse working all day                   0.30

   A Medieval water wheel                         3

   A Medieval wind mill                           5

   An early 18th-century steam engine            12

   The largest 20th-century steam 

                       power plants       3,500,000

   _____________________________________________________ 



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

Previous Episode | Search Episodes | Index | Home | Next Episode