College Physics

Book Preface

College Physics is intended for a two-semester college course in introductory physics using algebra and trigonometry. Our main goals in writing this book are

• to present the basic concepts of physics that students need to know for later courses and future careers,
• to emphasize that physics is a tool for understanding the real world, and
• to teach transferable problem-solving skills that students can use throughout their lives.

We have kept these goals in mind while developing the main themes of the book.

NEW TO THIS EDITION
Although the fundamental philosophy of the book has not changed, detailed feedback from over 170 reviewers (many of whom used the first edition in the classroom) and 10 class tests have enabled us to fine-tune our approach to make the text even more user-friendly, conceptually based, and relevant for students. The second edition also has some added features to further facilitate student learning.
Review and Synthesis with MCAT Review®

Eight Review and Synthesis sections now appear throughout the text, following groups of related chapters. The MCAT® Review includes actual reading passages and questions written for the Medical College Admission Test (MCAT). The Review Exercises are intended to serve as a bridge between textbook problems that are linked to a particular chapter and exam problems that are not. These exercises give students practice in for-mulating a problem-solving strategy without an external clue (section or chapter num-ber) that indicates which concepts are involved. Many of the problems draw on material from more than one chapter to help the student integrate new concepts and skills with what has been learned previously.
Improved Organization of Chapters 2 through 4
There are some areas of innovative organization in College Physics (see pp. xv–xvi). Chapters 2–4 have been further improved for the second edition:

• Based on reviewer feedback, the introduction of forces in Chapter 2 was simplified. All material involving surface tension, buoyant forces, Coulomb’s law, and electric fields was removed.
• Chapter 2 now has a larger number of quantitative examples and problems and has more examples that involve drawing free-body diagrams.
• Some reviewers felt that the treatment of vector addition was “too spread out” in the first edition. Sections 2.2–2.5 now provide a complete treatment of vector addi-tion. The examples start with one-dimensional problems and then progress to two dimensions.
• General definitions of position, displacement, velocity, and acceleration—using vector diagrams—are now presented in Chapter 3. Reinforcing the vector nature of these quantities helps students avoid the common misconceptions that can arise when they are defined first in one dimension and then redefined with different nota-tion in two dimensions. Once again, the examples that illustrate each concept start with the simplest one dimensional applications and then progress to two dimen-sions within each section.

Revision of Chapter 6
Chapter 6 was streamlined to give a clearer picture of the idea of energy conservation. Potential energy is introduced earlier in the chapter, using a simplified discussion of the connection between the work done by a conservative force and the change in potential energy associated with that force.
Revision of Chapter 15
Chapter 15 was revised to simplify the presentation of entropy and to eliminate nonstan-dard terminology. The first law of thermodynamics is now written ∆U = Q + W, consis-tent with the use of W in Chapter 6 to represent the work done on a system. This is the same sign convention used in most chemistry classes and is increasingly common in high school physics classes now that the Advanced Placement Physics B exam uses it.

Revisions to Problem Sets
Great care was taken by both the authors and the contributors to the second edition to revise the end-of-chapter problems. About 25% are completely new. The problems now have more variety in level: in particular, we increased the number of easier problems that help students gain confidence and reinforce new skills before they tackle more challenging problems.

Revised Art Program
The majority of reviewers of the first edition praised its innovative art program. However, reviewers also commented that some of the showcase illustrations were “dis-tracting” and “too large.” In response, we assembled a panel of experienced instructors to advise us on the illustrations and photos. The panel helped us identify the most useful showcase illustrations to retain for the second edition. They advised us on how to revise illustrations to make them clearer and more useful and on where to add graphs, dia-grams, simpler sketches, and free-body diagrams to enhance the text discussions and examples. The second edition increases the emphasis on simpler sketches and free-body diagrams similar to those that students should draw on their own homework or exams.
COMPREHENSIVE COVERAGE
Students should be able to get the whole story from the book. The first edition text was tested in our self-paced course, where students must rely on the textbook as their pri-mary learning resource. Nonetheless, completeness and clarity are equally advanta-geous when the book is used in a more traditional classroom setting. College Physics frees the instructor from having to try to “cover” everything. The instructor can then tai-lor class time to more important student needs—reinforcing difficult concepts, working through example problems, engaging the students in cooperative learning activities, describing applications, or presenting demonstrations.

INTEGRATING CONCEPTUAL PHYSICS INTO A
QUANTITATIVE COURSE
Some students approach introductory physics with the idea that physics is just the mem-orization of a long list of equations and the ability to plug numbers into those equations. We want to help students see that a relatively small number of basic physics concepts are applied to a wide variety of situations. Physics education research has shown that students do not automatically acquire conceptual understanding; the concepts must be explained and the students given a chance to grapple with them. Our presentation, based on years of teaching this course, blends conceptual understanding with analytical skills. The Conceptual Examples and Conceptual Practice Problems in the text and a vari-ety of Conceptual and Multiple-Choice Questions at the end of each chapter give stu-dents a chance to check and to enhance their conceptual understanding.

INTRODUCING CONCEPTS INTUITIVELY
We introduce key concepts and quantities in an informal way by establishing why the quan-tity is needed, why it is useful, and why it needs a precise definition. Then we make a transi-tion from the informal, intuitive idea to a formal definition and name. Concepts motivated in this way are easier for students to grasp and remember than are concepts introduced by seemingly arbitrary, formal definitions.
For example, in Chapter 8, the idea of rotational inertia emerges in a natural way from the concept of rotational kinetic energy. Students can understand that a rotating rigid body has kinetic energy due to the motion of its particles. We discuss why it is use-ful to be able to write this kinetic energy in terms of a single quantity common to all the particles (the angular speed), rather than as a sum involving particles with many differ-ent speeds. When students understand why rotational inertia is defined the way it is, they are better prepared to move on to the concepts of torque and angular momentum.
We avoid presenting definitions or formulas without any motivation. When an equation is not derived in the text, we at least describe where the equation comes from or give a plausibility argument. For example, Section 9.9 introduces Poiseuille’s law with two identical pipes in series to show why the volume flow rate must be propor-tional to the pressure drop per unit length. Then we discuss why ∆V/∆t is proportional to the fourth power of the radius (rather than to r2, as it would be for an ideal fluid).
Similarly, we have found that the definitions of the displacement and velocity vec-tors seem arbitrary and counterintuitive to students if introduced without any motiva-tion. Therefore, we precede any discussion of kinematic quantities with an introduction to Newton’s laws, so students know that forces determine how the state of motion of an object changes. Then, when we define the kinematic quantities to give a precise defini-tion of acceleration, we can apply Newton’s second law quantitatively to see how forces affect the motion. We give particular attention to laying the groundwork for a concept when its name is a common English word such as velocity or work.

WRITTEN IN CLEAR AND FRIENDLY STYLE
We have kept the writing down-to-earth and conversational in tone—the kind of lan-guage an experienced teacher uses when sitting at a table working one-on-one with a stu-dent. We hope students will find the book pleasant to read, informative, and accurate without seeming threatening, and filled with analogies that make abstract concepts easier to grasp. We want students to feel confident that they can learn by studying the textbook.
While learning correct physics terminology is essential, we avoid all unnecessary jargon—terminology that just gets in the way of the student’s understanding. For exam-ple, we never use the term centripetal force, since its use sometimes leads students to add a spurious “centripetal force” to their free-body diagrams. Likewise, we use radial component of acceleration because it is less likely to introduce or reinforce misconcep-tions than centripetal acceleration.