Writing a physics textbook is a tricky business. Make a book too comprehensive, and it quickly becomes unwieldy [one study (“Textbook Weight in California: Analysis and Recommendations,” California State Board of Education, May 2004 ⟨http://www2.cde.ca.gov/be/ag/ag/may04item21.pdf⟩) found that high school physics texts average above 6 pounds]. But leave out examples or explanatory text, and a textbook becomes less a teaching tool and more a handbook for practicing physicists (e.g., Jackson's classic electrodynamics text). So what's an author to do? One useful strategy for producing a good physics textbook is to narrow its scope, which thereby (possibly) limits its readership but allows for the kind of time and attention to detail required for student understanding. A recent book, Physics from Planet Earth: An Introduction to Mechanics, by Amato and Galvez, utilizes this strategy to good effect. The result is an undergraduate mechanics text that is a pure pleasure to read.
The first thing that stands out about this is book is that it is themed. That is, everything is presented as part of an over-arching story; namely, that of Earth and its place in the cosmos. All of the basic building blocks of introductory mechanics are there: conservation of momentum and energy, force and Newton's Laws, circular motion, torque, and so forth. But each building block is carefully placed into an ongoing narrative, one that is heavy on history and astronomy. For instance, in Chapter 2, after vectors are introduced, one of the very first worked examples is a comparison between the Copernican and Ptolemaic world-views. The authors are not fooling around—the geometry here is immediately challenging—but for a student interested in astronomy, the material is fascinating.
There are advantages and disadvantages to this approach. On the one hand, we found that the emphasis on history and astronomy made the book more engaging to read, and made the material more approachable. But this sharper focus might put off some students, whose interests may lie along other lines. In our own courses, we would be inclined to use this text in a sophomore-level mechanics course, aimed at students who already have some exposure to elementary mechanics. In a sense, the title of the book itself is a little misleading: the book is less an “introduction to mechanics” and more of a “mechanics text for astronomy majors.” But that's a minor quibble, and it shouldn't detract from the book's many virtues.
Among the best of these virtues are the numerous creative problems found at the end of each chapter; most have multiple parts, most are challenging, and many involve astronomy. As just one example, problem 9.19 has students calculate the Sun's speed and acceleration relative to the galactic plane, based on stellar density data. We non-astronomers found problems like this quite fresh and original.
Another virtue is this book's emphasis on conservation laws. In the preface, the authors write, “The three basic conservation laws (momentum, energy, and angular momentum) are introduced as fundamental laws of nature, from which secondary concepts such as force and torque are derived.” This is a more modern approach, in which symmetry arguments are fundamental—they are the starting points for all further investigations.
In summary, we would recommend this book for any introductory undergraduate mechanics course, with the proviso that there is a heavy emphasis on history and astronomy. Whether that's a plus or a minus depends on your target audience, of course. But the book does remind us—in the title, particularly—that it is mostly through physics that we have discovered Earth's place in the universe.
Jeffrey Lawson is a professor of mathematics and Matthew Rave is an associate professor of physics, both at Western Carolina University. Jeffrey's research interests are in geometric mechanics and field theories, while Matthew's include low dimensional solid state systems, along with quantum interference and decoherence. They have collaborated on problems involving geometric phase.