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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