This Author Is a Parent’s Best Friend : --”Perpetual Motion.” From THE WAY THINGS WORK: FROM LEVERS TO LASERS TO COMPUTERS--A VISUAL GUIDE TO THE WORLD OF MACHINES by David Macaulay (Houghton Mifflin: $24.95; 384 pp., color illustrations, indexed).

“Even with the very best bearings, lubricants and streamlining, a little friction still remains. Without a continual supply of fuel or electricity, friction gradually consumes a machine’s kinetic energy . . . and the machine slows down and stops. This is why the goal of inventors throughout the ages to build a machine capable of perpetual motion can never be achieved at least, on Earth.

“In space, matters are different. No air exists to cause friction and slow a spacecraft. Once launched into space, a spacecraft is freed from friction. It can continue to move in perpetuity without even firing its engine again. Thus, in the space probes voyaging outward toward the stars, we have achieved perpetual motion, a pure movement governed only by the celestial mechanics of gravity.”

“The Way Things Work” is a godsend for any parent who has ever been posed such inevitable questions from the kids as: “How do light bulbs make light?” or “Why can a jumbo jet fly?”

Author and illustrator David Macaulay has put together a remarkable primer on the principles behind the machines that our civilization depends upon and often takes for granted. Macaulay’s clever, amusing illustrations and his crisp language can help the most un-technical of readers learn the mechanics of the can opener, the zipper, rack-and-pinion steering, window shades and nuclear power, to name a few. In other words, if it’s a machine, it’s here, and Macaulay can help you understand how and why it works in precise and lively language. The way Macaulay sees it, you can only understand how a machine works if you understand the principles that govern its actions. Therefore, he’s organized his book by principles rather than by the historic development of particular machines. Thus, he establishes relationships between the zipper and plow, the Aqua-lung and the toilet tank, music and the tape recorder.

Macaulay is a splendid visual humorist--his drawings of a woolly mammoth appear throughout the volume as a sort of mascot leading us through the scientific explanations, looking sometimes as silly as we feel not understanding how all these things that we take for granted work.

“The Way Things Work” isn’t exactly the kind of book you’d read cover to cover (unless you’re a techno-freak). But the strength of Macaulay’s book, it’s genius actually, is that one needn’t devote a tremendous amount of time to each particular section or article in order to come away from the book with some understanding, some new knowledge or insight. This isn’t a book to agonize over. It fact, it’s both fun and fascinating to peruse or merely flip through. You’ll find yourself drawn to read about such complex items as jet engines and nuclear power, no matter how fearful you are of technology.

Keep the book a secret from the kids for a while and study up on the explanations of questions you’re anticipating. Let Macaulay make you look smarter than you think you are. The kids will certainly be impressed--and you’ll be getting a real education in the bargain.