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from The Textbook Letter, September-October 1998

A good publication for your professional library

Conceptual Physics for Parents and Teachers:
volume 1, Mechanics

1998. 179 pages. ISBN: 941051-64-1. Focus Publishing,
P.O. Box 369, Newburyport, Massachusetts 01950.

This Skillfully Written Book Is
Paul Hewitt's Best Work to Date

Sumner P. Davis

Paul G. Hewitt is an instructor in physics at the City College of San Francisco. He is also a highly successful writer, best known for his books titled Conceptual Physics. He has created two such books -- one for high-school students, the other for college students who are not majoring in science but who want to get some perception of what physics is all about. (The college version often serves as the textbook for courses facetiously called "Physics for Poets.") I myself have used Hewitt's books for helping high-school teachers to gain an essential knowledge of physical science, so that they and their students can discuss physics with a degree of understanding that goes beyond using definitions, rules, laws and equations to find answers to problems.

Hewitt recently launched a new series of books, in paperback, called Conceptual Physics for Parents and Teachers. The first volume in the series is now in hand, and it is titled Mechanics. This is not surprising, since mechanics -- which includes the study of motion, forces and momentum -- is the traditional starting point for appreciating the physics that is all around us. The publisher promises that four more volumes (to be titled The Atom and Matter; Electricity and Magnetism; Sound and Light; and Relativity) are in the works.

In the preface to Mechanics Hewitt tells us that he is aiming at "parents and teachers who didn't learn much physics in their own student days." He should find a ready audience among science teachers, for this reason: It is an unfortunate fact that many teachers nowadays are required to give courses dealing with aspects of science in which they themselves have had no formal instruction. Hewitt says that he is attempting to equip his readers with a basic knowledge of physics, so that "you can better appreciate the physics that is all around you, and better teach what you've learned to the young ones."

In Mechanics, he has succeeded. I've read Mechanics as I might read a novel, eager to see what hypotheses, laws, theories, predictions, illustrations, questions, and answers Hewitt would come up with, and in what order, as the book unfolded. I almost finished reading it clear through in a single sitting! Hewitt has an uncanny ability to anticipate his reader's questions and to answer them skillfully by constructing models, by drawing pictures, or by telling stories which illuminate the thought-paths that he and the reader are exploring.

This book is definitely one for adults. Hewitt assumes that his reader is accustomed to maturity in the use of language, has some skill in grasping new ideas, and is willing to read thoughtfully. He writes carefully, but in a style that is never dry, and his pages are often enlivened by diagrams and cartoons. (These illustrations, many of which have appeared in his earlier books, aren't mere adornments or clever devices to titillate some casual interest. They are important elements in Hewitt's way of teaching science.) About half of the pages have boxed questions, which soon are followed by their boxed answers. I find these to be most helpful and not at all distracting.

The introductory material in Mechanics includes a two-page "Physics Dictionary" in which Hewitt, using much the same language that I use all the time in talking with students and teachers, defines six important scientific terms: fact, hypothesis, law, theory, concept and prediction. He also explains that a word's scientific meaning may be profoundly different from its vernacular meaning. For example: In everyday usage, fact often designates something that is held to be absolutely "true" and immutable -- but in the vocabulary of science, fact carries no such implication. A scientific fact is never immutable and is always tentative. It is a provisional inference derived from observations of nature, and it may be modified or discarded as new observations are made.

Such information is particularly valuable when we encounter students who scorn science because they don't understand its intellectual structure. Moreover, this information is indispensable when we must instruct students who have fallen prey to pseudoscience. Pseudoscientists -- whether they are promoting astrology, acupuncture, pyramid magic, "creation-science" or some other set of delusions -- regularly use scientific words like fact, theory, hypothesis and prediction in false and misleading ways. They do this to foster the notion that their superstitions are supported by "science," and they infect their followers with completely wrong beliefs about what science is, about how science works, and about what scientific statements mean.

Now let us look at the body of Hewitt's book. Hewitt starts out with the concept of equilibrium, proceeds to linear motion and to Newton's laws, and then presents chapters called "Momentum," "Energy," "Rotational Motion," Gravity" and "Projectile and Satellite Motion." Throughout, he concentrates on choosing his topics well, rather than trying to make his chapters all-inclusive.

Is Hewitt's physics any good? Yes, I think it is. He does not mislead or short-change his readers by oversimplifying or by dealing in faulty concepts, and he has a good sense of what should be kept from the past and what should be modified or eliminated. He has eliminated, for example, the traditional, ponderous attempt to distinguish mass from weight. Efforts to use the terms mass and weight in strictly correct ways can lead to disagreements even among physicists -- so Hewitt, when he first uses these words, avoids profundity and elects to define weight in this way: "Weight is the gravitational force exerted on an object by the nearest most-massive body (locally, the earth)." Later, though, in the chapter on gravity, he explains that there is more to it than that, and he gives a more detailed discussion of mass, weight and weightlessness. Questions are presented at exactly the appropriate level, and the reader is left with a clear sense of what mass and weight mean in any practical case.

The final chapter, "On Science," forms a worthy capstone to Hewitt's work. Here Hewitt gives us his insights into the philosophy of doing and thinking science, and he assesses accurately the roles of mathematics, scientific terminology and the scientific method as he describes how we progress in our understanding of the natural world. He also provides sections titled "Pseudoscience," "Science, Art, and Religion," and "Science and Technology."

Hewitt's strengths as a writer lie in the simplicity, clarity and succinctness of his exposition. The reader of Mechanics probably won't be able to help a student crunch through the mathematical problems presented in a regular physics textbook, but he will be able to discuss the physics intelligently and will be able to assess the reasonableness of any calculated answer.

Mechanics represents the best of Paul Hewitt's work to date, and I recommend it.


Sumner P. Davis is a professor emeritus in the Department of Physics at the University of California at Berkeley. He continues to teach there, giving an advanced laboratory course for physics majors. He has taught in Berkeley's "Science for Science Teachers" program, which presents physics to middle-school teachers, and he has served on the Golden State Examination Committee for Coordinated Science, which seeks to identify exceptional high-school science students.

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