The best high-school physics book

Editor's Introduction -- Here is a review of the 1991 version of PSSC Physics, the best high-school physics textbook that we have seen.
from The Textbook Letter, May-June 1992

Reviewing a high-school book in physics

PSSC Physics
1991. 621 pages. ISBN: 0-8403-6025-8. Kendall/Hunt Publishing Company,
2460 Kerper Boulevard, Dubuque, Iowa 52004. (The earlier versions
of this book were published by D.C. Heath and Company.)

An Outstanding and Inspiring Book,
Strongly Recommended

Lawrence S. Lerner

By the first years of this century, the physicist Robert A. Millikan had already acquired considerable reputation as a teacher, though he had not yet begun the experimental work that would make him immortal. In 1906 Millikan and his colleague Henry G. Gale wrote a schoolbook, A First Course in Physics, that dominated the teaching of high-school physics for the next decade or so. The aim of that book, in Millikan and Gale's own words, was "to present elementary physics in such a way as to stimulate the pupil to do some thinking on his own account about the hows and whys of the physical world in which he lives." In short, the book tried to show the student how to think like a physicist.

After World War 1, education in the public high schools underwent revolutionary change. The minimum age at which young people could leave school rose from 14 to 16 or 17, the high-school population exploded, and the schools themselves were democratized. No longer were they the elite institutions that they once had been.

Along with all the good that lay in that revolution came a trend toward weakening the content of courses and textbooks to accommodate the supposed needs and limitations of the democratized student body. (Today such weakening is called "dumbing down.") A First Course in Physics was not exempt from this trend: Though the book was revised and greatly simplified by Willard R. Pyle, a teacher at Morris High School in New York, and though it was retitled Practical Physics, it gradually was supplanted by newer texts that did not teach physics so much as they taught about physics. The idea that students of physics should learn to think like physicists was lost. The newer texts replaced real physics with illogical, error-filled, ain't-nature-grand material, and they avoided mathematics as if it were sex education.

This state of affairs persisted until the late 1950s. When I took high-school physics (in 1948 and 1949), I did not hear about Newton's laws until the end of the second semester. Except for a lot of calorimetry, I have no recollection of what I learned. But I do remember the wonderful moment in the summer of 1951 when, doing some reading for a college course, I suddenly saw the difference between weight and mass -- something that my high-school course had obscured in a cloud of poundals, pounds and slugs.

The next generation of students was more fortunate. The Soviet Union launched Sputnik in 1957, and suddenly everyone was interested in having young Americans learn physics. This virtually ensured the success of the Physical Science Study Committee (PSSC), a group of university and high-school educators that had been established at the Massachusetts Institute of Technology, in 1956, to develop a new high-school physics course. PSSC now found itself showered with almost limitless resources (mainly from the National Science Foundation), and it was able to undertake the work that led to the publication, in 1960, of the first edition of the high-school book PSSC Physics. Though written by a committee, PSSC Physics conveyed the same expertise and insight and spirit that, more than 50 years earlier, had graced the book written by Millikan and Gale.

I now have the pleasure of reviewing PSSC Physics in its seventh edition, dated in 1991. It is an outstanding book, and it offers today's students the same intellectual opportunities that the first edition offered to their parents.

The first sentence of the preface to this edition tells us that "PSSC Physics has been, and still is, a course for students who want a lasting reward and are willing to make the effort to achieve it." One might take this to mean that the book is for the "smart" student only. In fact, however, the student need not be "smart" but must be serious, must be literate, and must have done reasonably well in introductory algebra -- well enough to have learned to manipulate simple linear equations and to understand graphs.

The writers introduce the spirit of the book in a short and beautiful first chapter titled "Studying Physics," where they ask the student to consider the statement that "The sun rises in the east and sets in the west." They discuss how the accuracy of that statement depends on the location of the observer, and they present a graph showing how the azimuth of the setting sun deviates (in degrees north or south of due west) as a function of time (measured in days after the vernal equinox) for observers at different latitudes. Then come some beautiful problems aimed at immersing the student in a search for functional relationships in various situations. The chapter ends by alerting the student to the fact that insights gained during a consideration of sunsets can be extended to other questions as well.

The rest of the book is organized in a more or less standard way. The exceptions are interesting, although some are not pedagogically successful.

Kinematics and dynamics are initially presented in a one-dimensional context, so the student can come to grips with "real physics" immediately, before having to give attention to the mathematics of vector algebra. This seems to reflect a trend that can be observed in college-level texts too -- a trend of which I approve.

Chapter 2, a thorough study of the relations among position, displacement, velocity and time, is excellent -- the writers generally have worked with meticulous care. They err, however, when they introduce but fail to explain the term dimensions (page 19), the term extrapolated (page 21) and exponential notation (page 21). Similar oversights occur in other chapters, and the book as a whole shows too many of them. On page 40, for example, the unit cm/s2 is introduced without any explanation. On page 42 a figure relates instantaneous acceleration to the slope of the tangent to a curve, but there is no explanation of how one might draw such a tangent. On page 61 the magnitude of a vector is introduced without definition.

The writers approach dynamics, in chapter 3, by presenting careful experimental observations (and photographs) of the motion of a virtually frictionless puck. Because acceleration is associated with net force, introducing acceleration in the context of dynamics makes sense and complies with an important pedagogical rule: Never introduce a quantity until you are ready to use it. On the whole, however, the writers' handling of dynamics is less successful than their treatment of kinematics, and their introduction of the laws of motion is idiosyncratic: They designate the first law by the name "Galileo's law of inertia" (which is quite reasonable) and they call the second law "Newton's law," but they do not mention the third law at all. They give a beautiful discussion showing how, without having defined any unit of force, one can experimentally subject the frictionless puck to known multiples of some force that has been chosen arbitrarily. This is followed by a tricky introduction of the relation ma = F, which leads to a definition of mass. But then, without erecting any unit of mass or giving the student an opportunity to work with the second law, the writers introduce the subtle distinction between inertial mass and gravitational mass (page 47). I doubt that even the brightest student will be able to grasp that distinction at this early juncture.

The fundamental unit of mass, the kilogram, is introduced (finally) on page 48, but in a throwaway line that many students will simply miss.

Having presented experimental evidence derived from a frictionless system, the writers now deal with an apparent contradiction that troubles many students: The first law notwithstanding, common experience suggests that motion at constant velocity requires the application of a constant force. The writers resolve the contradiction by using an elegant argument from Galileo.

The introduction of vectors, in chapter 4, is satisfactory but could be clearer. One of the few serious mistakes in the book involves figure 4-17 (on page 65): The average-velocity vectors shown in the figure do not correspond correctly to the displacements of a body moving uniformly in a circle. Generally, however, uniform circular motion is treated cleverly. The writers' derivation of one important equation -- the one relating instantaneous acceleration, the radius of the circular path, and the period of revolution -- is brilliant but not transparent. The same can be said of their clever use of the centripetal acceleration to derive the expression for the period of a simple harmonic oscillator. And their partly graphical derivation of the important kinematic relations for constant acceleration is both brilliant and transparent.

Free fall appears after some brief discussion of the concept of a gravitational field (on pages 78 and 79). The discussion is well done, but its significance may elude the student. Surprisingly, the writers do not exploit this opportunity to show that inertial mass and gravitational mass are equal.

Chapter 6 introduces the concepts of kinetic and potential energy, then chapter 7 provides parallel treatments of gravitational force and electrostatic force. This is a good though unusual pedagogic approach. The discussion of electrostatic induction -- a topic thoroughly confused in most high-school and college texts -- is crystal-clear. However, the "experimental" derivation of the inverse-square behavior of the electrostatic force involves reading some values from a graph, and the numbers are wrong! The other essential element of Coulomb's law, the proportionality of force to charge, is extracted from experiments very clearly.

The argument for the inverse-square behavior of the gravitational force (starting on page 128) follows Newton's calculation of the acceleration of the Moon toward Earth. Unfortunately, the magnitude of the acceleration is left in the form a = 2.8 x 10-4 g. It would have been easy and dramatic to note the fact, far from obvious, that 2.8 x 10-4 is the square of 1/60 -- the ratio of Earth's radius to its distance from the Moon. When this point is raised in an exercise on page 131, it is too late and too obscure.

Newton's third law finally receives its due in chapter 8, in the context of conservation of momentum, as the writers analyze data extracted from excellent photographs of elastic collisions.

In chapter 9 the writers meticulously derive the ideal gas law from experiment, then offer an elegant and simple derivation of the kinetic theory of gases.

In chapter 10 the writers show some sloppiness as they return to electrical phenomena. They adumbrate the concept of a potential difference in such a way as to confuse the student who remembers Coulomb's law (from chapter 7), they confuse potential difference with electromotive force, they call the volt a "practical unit," they define the coulomb poorly, and they badly scramble their discussion of the proportionality constant, k, in Coulomb's law. The writers' zeal for deriving everything from experimental evidence is laudable, but they go too far when they try to describe an experiment for evaluating k. Their procedure could never be carried out with any precision. In any case, k is a defined quantity -- not one whose value is determined experimentally.

Chapter 11, "The Magnetic Field," includes many elegant arguments, notably the one that justifies the vectorial addition of magnetic fields that are superposed. In chapter 12, a discussion of elementary charges is based on variants of Millikan's oil-drop experiment and Thomson's e/m experiment, both so simple that the student can do them. Some of the rather difficult mathematical analysis is rendered tractable by lovely tricks, but the exposition of charged particles in crossed fields (sections 12-10 and 12-11) is not very clear. On the other hand, the writers do a superb job of describing and analyzing the Rutherford-Geiger-Marsden experiment, which gave evidence of the existence of the atomic nucleus.

Chapter 16 ("Particles at High Speeds: Relativistic Dynamics") is a brave attempt to derive relativistic dynamics by fitting curves to the results of a single experiment. lt is too sophisticated for all but the very best students, I fear, and it will fail to convince the knowledgeable teacher. In particular, the writers make too much of the effort to find a function that fits three experimental values for which no margins of error are given (section 16-2).

Chapters 17 through 19, dealing with waves and light, may be the best part of the book, characterized by wonderfully clear text and superb photographs. In presenting all the major phenomena, the writers use a minimum of mathematics but do not pull any of their punches.

PSSC Physics is a big book, so it is no surprise that the writers have put some important topics into "Optional Chapters" (chapters 21 through 28). Some of the material in those chapters is particularly fine: I note the discussions of heat engines and entropy (in chapter 22), Faraday's law (in chapter 25), the Hertzsprung-Russell diagram and its implications (in chapter 27) and atomic structure and spectra (in chapter 28).

As a whole, PSSC Physics is remarkably accurate. I have seen only one typographic error ("eleementary" in the second line on page 271) and only three or four misleading illustrations. [See "In the Land of the Midevening Sun" on page 12 of this issue.] As for flatly erroneous discussions in the text: The only ones that I have found are the ones that I have mentioned above.

The laboratory manual that accompanies PSSC Physics is strong and useful. It is intended for use with a carefully developed kit of materials, but teachers whose budgets can't accommodate the kit can devise home-made versions of many of the required items.

I recommend PSSC Physics strongly to teachers and students who are willing to expend the effort that this book so powerfully inspires.

Lawrence S. Lerner is a professor in the Department of Physics and Astronomy at California State University, Long Beach. His specialties are condensed-matter physics, the history of science, and science education. He served on the panel that wrote the State of California's 1990 Science Framework, which guides science education in California's public schools.


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