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from The Textbook Letter, Volume 12, Number 4

Reviewing a physical-science book for grade 8 or 9

Force, Motion, and Energy
2002. 150 pages. ISBN: 1-882057-12-0. Science Curriculum Inc., 24 Stone Road, Belmont, Massachusetts 02478.

Fine Scientific Insight, Masterful Pedagogy, Interesting Writing

Lawrence S. Lerner

It has been a long time, and a lot of textbooks ago, since I was an eighth- or ninth-grader, yet I have found Force, Motion, and Energy stimulating to read. Published by Science Curriculum Inc. (SCI), this wonderful book displays fine scientific insight, masterful pedagogy and interesting writing as it sets forth standard subject matter dealing with mechanics and heat. The sequence of topics is unorthodox, but the handling of those topics is almost impeccable -- logically, experimentally, and pedagogically. Moreover, I have not detected so much as one typographical error in the entire book.

Perhaps I should not be surprised to find that this book is so good, since the five authors of Force, Motion, and Energy include Uri Haber-Schaim, Reed Cutting, H. Graden Kirksey and Harold A. Pratt [see note 1, below]. These four created the superb textbook Introductory Physical Science, which SCI published in 1999 [note 2].

Like Introductory Physical Science, the present book is solidly founded on a fine collection of experiments for students to carry out. Force, Motion, and Energy can serve by itself in a one-semester course, or it can be used with Introductory Physical Science in a cogent one-year sequence.

The Teacher's Guide accompanying Force, Motion, and Energy is well written and useful. In particular, it is diligent in pointing out difficulties that students may encounter in doing some of the experiments, and is very helpful in explaining how the teacher and the student can deal with those difficulties.

An Elegant Series of Experiments

Force, Motion, and Energy begins with a careful exposition of the physical meaning of "force," based on experiments that the student performs with a spring scale. The ideas of proportionality and the proportionality constant are introduced immediately and are illustrated by Hooke's law. Next, the authors provide a careful and clear exposition of the concept of a unit, using the newton as an example. This is followed by a series of experiments with a pair of permanent magnets: The student finds that not all forces are directly proportional to displacement, and that some forces can act at a distance.

In an elegant series of experiments on sliding friction, SCI's authors expand the concept of the proportionality constant (now exemplified by the coefficient of friction). Then, in an ingenious extension of the earlier procedures in which the student used a spring scale, the authors present an experiment involving two such scales and a block mounted on a cart: The student uses the spring scales to exert a force on the block and an opposing force on the cart, and the student thus "discovers" Newton's third law. This approach is notable because it completely avoids a common source of confusion: On which bodies are the action force and the reaction force acting?

In chapter 2 the authors set out the concepts of weight, mass, volume, and density. Then, building upon their earlier discussion of proportionality, they elucidate pressure as the ratio of force to area. Pascal's law is introduced experimentally, as is Archimedes's principle.

In chapter 3, the authors introduce the vector. They elegantly put forth the parallelogram rule, and they show how the geometric addition of vectors allows us to understand such important systems as inclined planes. The student who masters this material will be thoroughly prepared to deal with the trigonometric addition of vectors at a later time.

Similarly, a sequence of qualitative experiments with air pucks provides insight into the relation between force and acceleration, paving the way for a formal, quantitative study of Newton's second law in a later course.

Chapter 4 covers distance, time, speed, and the equations that relate them. Chapter 5 deals with wave motion, emphasizing the important distinctions between the kinematics of waves and the kinematics of particles, and the student learns how the time lapse between S and P waves can be used to determine the distance to an earthquake source.

Chapter 6 ("Heating and Cooling") and chapter 7 ("Potential Energy and Kinetic Energy") are, to my mind, the cleverest in the book. At the beginning of chapter 6 the authors make clear that temperature changes can result from a wide variety of dissimilar events. They introduce the concept of thermal energy, discuss changes in thermal energy, and provide calorimetric experiments that point to specific heat capacity, heat of fusion, and the joule.

In chapter 7 the student employs some modifications of Joule's mechanical-equivalent-of-heat experiment to explore connections between thermal energy and gravitational potential energy, between thermal energy and elastic potential energy, and between thermal energy and kinetic energy. This work enables the authors to define energy quantitatively and with some rigor; I never before have seen this in a textbook for students at this level.

The book ends, somewhat abruptly, with an exposition of the law of conservation of energy, including a passage that hints at the second law of thermodynamics:

No process has even been observed in which the law of conservation of energy has been violated. However, not every process that satisfies the law will necessarily take place. Think of Experiment 6.2, Mixing Warm and Cool Water. We defined the cooling of the warm water as a loss of thermal energy so that the loss equaled the gain of thermal energy by the cool water. Imagine the opposite process. A quantity of water at some uniform temperature inside an insulated container separates by itself into two parts, one warmer and one cooler. This process never happens, although it would not violate the law of conservation of energy. . . . The law of conservation of energy tells us what is not possible. However, it is not sufficient to tell us what is possible. [page 131]

Some Suggestions for Improvements

Having praised this admirable book, I now should note some of its features that can be improved when the next edition is prepared:

I look forward to seeing all these deficiencies remedied in the next edition. In the meantime, I recommend Force, Motion, and Energy in the strongest terms possible. I wish that I had had its like when I was an eighth-grader!

Notes

  1. SCI is an honest company, and the persons who are listed as authors on the title page of an SCI book are really the book's authors. This is unusual. In typical books sold by the major schoolbook companies, the lists of so-called authors are fictitious and have been concocted to serve as sales-promotion features. For an examination of how fake lists of "authors" were invented and juggled in successive versions of a physical-science text issued by Glencoe/McGraw-Hill, see my review "Next Time, Glencoe Should Try to Get Some Real Authors" in The Textbook Letter, Vol. 8, No. 1. [return to text]

  2. See my review "This Book Is the Best, by a Wide Margin" in TTL, Vol. 10, No. 4. [return to text]

  3. The authors seem to know that their handling of basic mathematical ideas leaves room for improvement. In their Teacher's Guide, in a passage dealing with material in chapter 6 of the textbook, they tell the teacher this: "The mathematical reasoning in this section will very likely be difficult for your students unless they have a good mathematical background in proportions." If this is the case for material chapter 6, it must be the case, a fortiori, for material in chapter 1. [return to text]

  4. For many years, A.A. Michelson showed to visitors an equal-arm balance that he had set up in Ryerson Physical Laboratory at the University of Chicago. The pan on one arm was located on the third floor of the building while the pan on the other arm was suspended by a much longer linkage and was located in the basement. Michelson could readily show that this instrument was balanced only when the masses in the two pans were (slightly) unequal. [return to text]


Lawrence S. Lerner is a professor emeritus in the College of Natural Sciences and Mathematics at California State University, Long Beach. His specialties are condensed-matter physics, the history of science, and science education. His university text Physics for Scientists and Engineers was issued in 1996 by Jones and Bartlett Publishers, Inc. (Sudbury, Massachusetts).

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