from The Textbook Letter, November-December 1993
Reviewing a high-school book in physics
The High School Physics Program
1992. 676 pages. ISBN of the teacher's edition: 0-201-28652-1.
Addison-Wesley Publishing Company, 2725 Sand Hill Road,
Menlo Park, California 94025.
For High-School Physics,
This Textbook Is the Best
Sumner P. Davis
"What should we teach in high-school physics?" University professors
of physics used to hear that question fairly often from
secondary-school teachers, and the answer that many of the
professors gave was: Just teach them mathematics -- no physics.
We will teach them the physics that they need to know."
Why that reply? Because the professors were getting too many
students with little feeling for what science was all about, with an
unbalanced view of what was important, and with only a minimal
understanding of basic concepts in physics.
Now, with Addison-Wesley's splendid Conceptual Physics
available, there is no excuse for even asking the original question.
If every science student will learn what is in Conceptual
Physics, high-school graduates will have a sensible grounding in
scientific methods and the scientific attitude, as well as enough
factual knowledge to comprehend many of the technological challenges
that our society faces. When such students get to college, the
blending of formalism and mathematics with a deeper understanding of
physics will be easy and smooth because the students will already
have gained the necessary qualitative knowledge and the necessary
training in scientific thinking. We can't ask for more than that.
The author of Conceptual Physics is Paul G. Hewitt. In an
introductory note on page xi, he says that the book treats physics
"conceptually rather than mathematically . . . with equations
[serving as] 'guides to thinking' rather than recipes for algebraic
problem solving." In fact, there are almost no equations, and none
of the usual "formulas" for anything. Students will need some
algebra to appreciate proportion and ratios, and they will have to
be able to read graphs and tables of numbers.
On every page of Conceptual Physics it is easy to see the
touch of a master teacher who has probably made every mistake
imaginable in teaching, who has learned from his mistakes and from
the experiences of others, who his listened to criticism, and who
has changed his ways accordingly. Yet he has not sacrificed his own
sense of how to teach and how to communicate. This is
Hewitt's book, not a consensus book created by a committee.
Conceptual Physics is divided, in a fairly standard way, into
six units: "Mechanics" (constituting about 36% of the text pages),
"Properties of Matter" (10%), "Heat" (10%), "Sound and Light" (20%),
"Electricity and Magnetism" (17%), "Atomic and Nuclear Physics"
Each unit comprises several chapters, and each chapter ends with a
review that has several parts. The "Concept Summary" is a statement
of what the student should have learned and should be able to
articulate. The "Important Terms" list presents words or phrases
that the student should be able to define or explain readily. The
"Review Questions" are short-answer questions that focus on
definitions and concepts. The "Think and Explain" problems often
are open-ended, having no single "right" answer. And some of the
reviews also include a hands-on "Activity." The reviews are complete
enough to eliminate the need for a study guide.
The text pages are embellished with sketches, cartoons, drawings,
photographic reproductions, boxed questions, and other items that
can help the student to visualize and understand what the text is
saying. These auxiliary items are not overdone and are not
distracting. They remind me of how a creative lecturer uses a
What's in it for the teacher? The teacher's edition of Conceptual
Physics opens with ten pages of promotional hype and
advertising. These are absolutely unnecessary, and having them
appear in the book is insulting. Next come 35 pages of "Full Answers
to [the] Think and Explain" problems in the chapter reviews. These
answers are good, but an experienced teacher will not regard them as
"full." In the chapter reviews themselves, the teacher finds short
(usually one-line) answers to questions that are posed to the
student. These answers are helpful and are especially useful to the
teacher who has studied physics only briefly.
Let's now look through the text to see what sticks out at first
reading. Chapter 1, "About Science," evidently reflects the
philosophy that Hewitt has worked out during his many years of
teaching. It is useful, but perhaps more interesting to an adult
reader. I can't imagine that many students will do any more than
glance at it. The cartoon characters say things such as "Facts are
revisable data about the world. Theories interpret facts. . . .
Science is about cosmic order. Religion is about cosmic purpose.
However, I learned something from this chapter, as I did from every
other chapter that I read.
In the unit on mechanics, Hewitt skillfully avoids pitfalls as he
discusses motion and elucidates speed, velocity and acceleration. He
gets the vectors right, but he also is able to explain that the
scientific meanings of the words speed and velocity
differ from their meanings in everyday language. He distinguishes
between center of gravity and center of mass, yet he does this in a
way that leaves the students' common experience intact; and he
follows up, somewhat later, by illustrating why the difference is
important. The chapters on gravitation and satellites are superb.
Want to know about weightlessness, tides, black holes, satellites,
relativity? They are all here, with no misconceptions that later
will have to be unlearned.
By the time I finished Unit II ("Properties of Matter") and Unit Ill
("Heat"), I could see that Hewitt has combined, in a knowledgeable
way, topics that less sophisticated writers usually treat
separately. Our surroundings really make sense and are
understandable as an integrated whole.
Unit IV ("Sound and Light") is full of answers to everyday
questions, and Unit V ("Electricity and Magnetism") is full of
physics and engineering. How I wish I'd read material like this
during my own days in high school! The pictorial representations
are easily translatable to what we see in practice, and there is an
unusually smooth transition from the pictorial to the schematic
depiction of circuits.
In the final unit ("Atomic and Nuclear Physics"), the material has
been chosen and presented well, but the unit is rather brief. It
builds on earlier chapters about properties of matter, but it is
little more than a summary of quantum and modern physics. There is
nothing about superconductivity, lasers, plasma physics, or particle
physics. There is no hint that today's "state of the art" physics
bears little resemblance to the physics of just a few years ago.
Hewitt evidently believes that these topics are best left to college
courses. That is a defensible judgment.
Are there any errors? Yes. On page 221, the text states that
astronauts traveling at 99% of the speed of light could make a round
trip to a distant star in 22.6 years, but that light itself would
take 22.8 years to make the same trip. And on pages 375 and 376, in
the four figures illustrating bow-wave and shock-wave patterns, the
lines representing the fronts should be drawn tangent to the
circles, not intersecting them.
No text can satisfy everyone, none can cover every possible topic,
and none is so good that it can't be made better in the future.
Right now, however, Hewitt's book is a winner, in terms of both
content and pedagogy. Of all the high-school physics texts that I
have seen (including the conventional, strongly mathematical ones),
Conceptual Physics is by far the best.
The Laboratory Manual that accompanies Conceptual
Physics looks as good as the book. It can easily stand on its
own and can be used in conjunction with a different text, but it is
definitely a cookbook. Any intellectual content or understanding
must be supplied by the teacher (for whom the manual provides good
notes). I believe that even a person who has not had any
physics-laboratory experience, but has read Hewitt's book, can complete
every one of the experiments that the manual describes.
This Book Is Easy to Read,
but It Has Too Many Errors
The subtitle of Addison-Wesley's book Conceptual Physics
serves to distinguish this high-school text from HarperCollins's
Conceptual Physics, which is a college text. Both books are
by the same author: Paul G. Hewitt. The college version was
introduced in 1971 and has been revised six times, so I am surprised
to see that the high-school version, which is similar to the college
book in many respects, retains so much erroneous material.
The readers of this review should be aware of some of my biases. I
appreciate the emphasis on conceptual physics, both for high-school
courses and for introductory college courses. To me, conceptual
physics means physics presented in a way that promotes a general
understanding of physical phenomena (along with a gut feeling for
what is going on), and I would expect any conceptual-physics book to
display sound reasoning and clear explanations. I do not feel that
the present book lives up to such expectations.
Some of the errors are familiar to me because I have seen them in
Hewitt's college text or in the first edition of this high-school
book (published in 1987). I have directed Hewitt's attention to many
of these errors, and to others as well, both in personal
communication and in my published writings. Indeed, I am one of the
persons whom Hewitt thanks, on the "Acknowledgments" page of
Conceptual Physics, for "suggested improvements." In certain
cases he seems to have made changes in response to my suggestions,
but the changes have not always been adequate. In other cases there
have been no changes at all.
Many teachers favor Conceptual Physics, and often use it as a
supplementary text, because students read it and like it. The
writing is not demanding, Hewitt's cartoon-like drawings provide
comic relief, and his diagrams are usually helpful in illustrating
the topics under discussion. (Hewitt was a commercial artist before
he began to study physics, at age 27.) Sometimes, however, the
artist overshadows the physicist. For example, in illustrating the
addition of two forces acting on a horse-drawn cart, it is not
helpful to show the horse exerting a force on the cart while a man
pulls on the horse (page 67). Similarly confusing are the curve
ball" diagrams, which show air moving in one direction while the
ball moves in another. This is an artistic attempt to combine, in
each diagram, the views from two different reference frames (page
Conceptual Physics covers the usual array of main topics --
from mechanics to nuclear physics -- but it does not strive for the
encyclopedic completeness often found in high-school physics books.
This seems proper, but Hewitt should have omitted even more material
when he could not discuss it adequately. For example, the passage
on using a galvanometer to measure voltage (page 560) seems
inadequate and can only serve as material for memorizing.
At the same time, Hewitt has usually resisted the temptation to load
this book with "modern" topics. The three major exceptions to this
rule are his serious attempt to explain relativity (chapters 15 and
16), his section on black holes (page 186), and his inadequate
discussion of muon-induced cold fusion (page 631).
There is little use of mathematics in Conceptual Physics, and
one wonders whether the book would be better if there were even less
of it. Some of the mathematics that Hewitt uses is rather peculiar.
In discussing the law of gravitation, for example, he claims that
the universal gravitation constant, G, "plays the same role
in the gravitational force equation that pi plays in the
equation for the circumference of a circle," and he says that the
values of both pi and G can be obtained by solving
the respective equations in which they appear (page 166). If this is
supposed to be a general statement about constants, it seems
unnecessarily involved. It certainly blurs an important difference
between the constants in question, because pi can be
calculated with paper and pencil, but G has to be obtained
experimentally. Furthermore, Hewitt correctly states that the
numerical value of G (unlike the value of pi) depends
on the choice of units, but he seems to forget this when (on page
496) he says, "The small value of G indicates that gravity is
a weak force . . . ."
A Regrettable Choice
During his discussion of accelerated motion and free fall (on page
18), Hewitt again seems to show little appreciation for the meaning
of mathematical expressions. In a footnote, he points out that if a
falling object has an initial velocity, one must combine that
velocity with the velocity due to gravitational acceleration. Then
he says, "This book will not be concerned with such added
complications." Nonetheless, motion with initial velocity is
discussed numerically on the same page (for the case of a ball that
is thrown upward) and on the next page (in a discussion of velocity
and acceleration during the first two seconds of free fall). I find
it regrettable that Hewitt reinforces a student's aversion to math
instead of showing how one algebraic expression makes possible the
general analysis of all free-fall situations, regardless of whether
the falling body does or does not have an initial velocity.
In his introductory sections about history and philosophy and
attitudes, Hewitt says that "scientists, like most people, have a
vast capacity for fooling themselves." There are examples of this
phenomenon in Conceptual Physics itself. For example, on page
339 Hewitt discusses at length the proposition that "under some
conditions hot water will freeze faster than warm water." Instead
of examining factors that (in a poorly controlled experiment) might
produce such a paradoxical result, he presents the result as if it
were reasonable, and he tries to relate it to the water's large
latent heat of vaporization. On page 295 he seems to imply that
there are forces (such as those due to differences in fluid
pressure) to which Newton's third law does not apply.
There are some "Review Questions" at the end of each chapter,
usually asking for phrases or facts that can be found in the
chapter's text. There are also more general questions, which are
well described by the title that Hewitt has given to them: "Think
and Explain." Unfortunately, some of these are presented in
misleading ways. For example, on page 582 a question asks for the
turns ratio of an induction coil, acting as a transformer, that
produces 24,000-volt sparks from an interrupted, 12-volt direct
current. The answer given in the teacher's edition is 2,000, but
this overlooks the fact that the induced voltage depends partly on
the rate at which the direct current changes with time. The
induction-coil question has no easy answer.
For this review I have selected a few typical examples from among
the many errors or misleading presentations in Conceptual
Physics. I have done this to help my readers decide whether the
book's accessible style, which has won a favorable response from a
relatively large number of students, can offset the disadvantages
arising from the confusion in Hewitt's physics. Some of this
confusion becomes apparent only if one studies the text with great
In response to my critical comments about Hewitt's earlier books,
some of my colleagues have looked closely at those books and have
noticed details that they previously had overlooked. Their opinion
seems to be that Hewitt sometimes shows a good grasp of physics, but
that his books would be much better if he could work with someone
who had a deeper understanding of the fundamentals. Their view, I
believe, is that Hewitt is a talented teacher who has an inviting
technique, and that improved versions of his textbooks could have
great educational value.
Sumner P. Davis is a professor of physics and a Distinguished
Teacher at the University of California at Berkeley. For the past
nine summers he has taught in Berkeley's "Science for Science
Teachers" program, which presents physics to middle-school teachers.
He is also a member of the Golden State Examination Committee for
Coordinated Science, which seeks to identify exceptional high-school
Mario Iona is a professor emeritus in the Department of Physics at
the University of Denver. He writes a column for The Physics
Teacher, analyzing erroneous and misleading material in science
textbooks and journal articles. When the American Association of
Physics Teachers gave him its Millikan Lecture Award in 1986, his
acceptance speech was entitled "Why Johnny Can't Learn Physics from
Textbooks I Have Known."
Addison-Wesley issued another version of Conceptual Physics
in 1997. Then Addison-Wesley merged with Longman Publishers to form
a company called Addison Wesley Longman, and this company produced a
"new" version of Conceptual Physics in 1999. To find reviews
of the 1997 and 1999 versions, consult our Index List.
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