What is New in the Third Edition

General issues

The primary goals for the 3rd edition were

- Increasing professors' flexibility by making more chapters optional,
- Improving the pedagogy for certain topics,
- Improving the layout (particularly regarding what appeared on facing pages),
- Adjusting chapter lengths to even out the pace,
- Increasing the number and quality of homework problems, and
- Correcting errors.

The following is a list of changes that affect all units:

- New problem types. The "Synthetic" homework-problem type has been split into two new types: "Modeling" and "Derivations." Problems in the Modeling category now always involve constructing models at some level and usually involve bringing multiple ideas together to address a realistic situation. Derviation problems are focused on more theoretical or mathematical issues. Some are quite simple, but some can be quite challenging. In the 2nd edition these distinct problem types were confusingly combined.
- Class-activity problems. The "Basic" and (less often) "Modeling" categories include some new multi-part problems especially designed to serve as good classroom activities. These problems sometimes guide students in probing a concept from multiple directions and sometimes serve as an "active example" that guide students step-by-step through a challenging calculation. Look for problems with four or more parts.
- Vector magnitudes. The text now exclusively uses absolute-value bars around a vector symbol to indicate the magnitude of the vector. This replaces both the mag( ) notation and the plain italic symbol as symbols for a vector magnitude. We found that (in spite of explicit instruction), many students failed to interpret the plain symbol correctly, but the mag( ) notation was too cumbersome. Unit C now includes explicit instruction (and some exercises and problems) in correctly interpreting conventional notation for vectors, vector components, and magnitudes, but also uses the new notation to help avoid student confusion.
- Problem-solving frameworks. The new edition takes a new and more flexible approach to giving students guidance in problem solving. Units C and N still instruct students on constructing solutions that involve translating, modeling, solving, and checking, and also on what solutions of various types should contain, but the instruction no longer requires a certain format, using cartoon balloons, interaction diagrams, or the like. Rather students are given checklists of things to include and are guided in recognizing how the crucial elements appear in example solutions. New exercises give students practice in these metacognitive skills.
- Example Layout Changes. A new example layout that encloses the example makes it easier to see (literally) what is actually inside each example.
- In-chapter exercises. The 2nd edition had too many in-chapter exercises to make it realistic to encourage students to work them as a normal part of active reading. The 3rd edition now usually has three (sometimes two and sometimes four) exercises per chapter, and they are now more carefully chosen to explore critical issues, so that they are more worth students' valuable time. Answers are still provided in the back.
- Work. The 2nd edition's approach to work was somewhat incomplete and potentially misleading, particularly when handling deformable objects. The 3rd edition now has a much more careful development of work. See the discussion of changes in Unit C for more details, but this change does affect other units as well.
- Short answers. At the request of many, many students, the 3rd edition now includes short answers to roughly half of the homework problems at the back of each unit. The selected problems are not always the odd-numbered problems (though this was the default), but have rather been chosen so that the answers might simultaneously provide helpful guidance for students but at the same time not give the problem entirely away.
- Under-performing features omitted. The chapter openers no longer include menu-like chapter location diagrams, and the unit volumes no longer include glossaries or symbol lists near the ends. We could not find any evidence that these features were really valuable to anyone, and the glossaries and symbol lists required a lot of work to maintain.
- Web-based supporting apps. We are in the process of rewriting the software associated with the course so that it becomes entirely web-based. This will end the need to actually download the apps, and they will run on any device with a browser.
- Web-based solution viewing. We are overhauling the process by which professors and students can view problem solutions. The new process will be web-based and (after a professor has been vetted) will no longer involve the author in individually posting files.
- SmartBook and Connect technologies. The textbook has now been fully integrating to various McGraw-Hill computer technologies. SmartBook® is an ebook version of the text with certain features intended to enhance active reading. Connect® is a web-based assignment and assessment environment. Follow the links for more information.

UNIT C

Here is a list of important changes in the 3rd edition of unit C:

- More discussion of model-building. The text now discusses the process of model-building more explicitly and in more detail, and also presents (literally) up-front discussion of tricks and techniques such as approximation, unit conversion, and dimensional analysis.
- The first few chapters are reorganized to provide a more logical flow.
- Problem-solving checklists and commented examples provide a better, more flexible approach to teaching students expert-like problem-solving styles.
- Vector conservation laws first. In this edition, angular momentum now immediately follows momentum conservation. These conservation laws have many similarities become more apparent when they appear together.
- Chapter C7 can be delayed or omitted. This chapter, the second of the two chapters on angular momentum, now contains the more difficult and mathematical material involving the vector cross product. This material is important for chapters N4, N11, and N12, but nowhere else. One can therefore delay to make the course's beginning a bit easier. Alternatively, it can be omitted entirely if you spend a bit of time before chapter N4 presenting the cross product definition of torque.
- The energy chapters have been reorganized to even out the pace and provide a better logical flow. In particular, the process of drawing and interpreting potential energy diagrams has been separated from the material on bonds. Chapters C8 and C9 alone now provide (barely) sufficient background for all the other units.
- Two-body systems with comparable masses are described in more detail.
- The text now provides a better exposition of energy concepts, more consistent with the approach outlined by John Jewett in a series of articles for Physics Teacher. First and foremost, this means that the text now carefully defines work (in a way consistent with thermodynamic work). K-work (alas) is gone: the book now more correctly treats the connection between an object's kinetic energy and the dot product of net force and CM-displacement as a consequence of the momentum-transfer principle. The book now treats rotational energy as a form of internal energy (this is more consistent with the definition of internal energy as energy inside an object's boundary), and allows for energy transfer modes other than heat and work. The book also now discusses modes of heat transfer. This provides a clearer, more complete, and pedagogically superior treatment of energy.
- Chapter C14 (Collisions) is now optional (though still useful for chapters R8 and R9).

UNIT N

Unit N did not receive much modification compared to most of the other units, but users of the 2nd edition will noted these changes:

- Chapters N1 and N2 now contain a streamlined version of what was in chapters N1 through N3 of the 2nd edition, reducing the unit's length by one chapter.
- Trajectory diagrams now start at t = 0. The way that trajectory diagrams in the 2nd edition started a half-step in the past proved endlessly confusing to students. The new approach to constructing a trajectory diagram now more logically starts with both position and velocity defined at t = 0, and constructs new positions at integer time-steps after t = 0.
- The presentation of conic sections is now simpler and more accessible.
- Chapter N11 is now the capstone and N12 is optional. A reorganization of the planetary orbit material means that chapter N11 now completes the discussion of the unit's "great idea." Chapter N12 now focuses entirely on the connection between conservation laws and orbits, and can be omitted (nothing else depends on it).

Unit R

Unit R also received only a handful of changes:

- Chapters R1 and R2 now contain a streamlined version of what was in chapters R1 through R3 of the 2nd edition, reducing the unit's length by one chapter. Chapters R2 through R4 now discuss the three kinds of time in sequence.
- Boosts can now be negative. Requiring that the Other Frame move in the +x direction relative to the Home Frame proved to be a restriction without a real purpose. Beta is now defined to be the x component of the Other Frame's velocity relative to the Home Frame.
- The 3rd edition now uses hyperbola graph paper more extensively, and gives students more explicit instruction in how to use that graph paper.

UNIT E

This unit was completely rewritten for this edition, almost from scratch. It therefore bears little resemblance to the 2nd edition, and though it is a bit closer to the "draft 3rd edition" that has been available for some years, it is still very different.

The core goal for this unit was to reduce the pace by about 30% compared to either of the previous editions. The author, after consulting with a number of users, has done this by cutting about 20% of the material overall (mostly by streamlining and reorganizing the presentation) and spread the remaining material over 18 chapters instead of 16.

Another goal was to provide more flexibility. Chapters E7 and E14 are now optional, so a professor can still teach the unit in 16 class sessions if necessary. Indeed, chapter E11 now presents the unit's "great idea" and nothing beyond this chapter is needed for any unit, so in principle, one could present a fairly easy version of this unit (without Maxwell's equations) in 10 or 11 class sessions. Professors also have more freedom to choose the level of the class by choosing the types of homework problems and class activities.

Unlike the 2nd edition, but like the "draft 3rd edition," this unit focuses on the differential versions of Maxwell's equations without ignoring the integral versions). However, the author has taken advantage of almost a decade of teaching from the "draft 3rd edition" to improve the pedagogy in many ways, making the presentation significantly simpler. Most importantly, multi-part problems E12M.1 and E13M.1 walk students step-by-step through the process of calculating fields using Gauss's and Ampere's laws (respectively) for non-trivial situations. We have found that having students work these problems as class activities makes a huge difference in their comfort level with these laws. After we made this change, students given instruction in both the differential and integral forms and given the choice of which to use on a test question almost universally chose to use the differential forms (and most used them correctly).

The integral treatment now appears in the optional chapter E14. This chapter is also significantly simpler than the corresponding material in the "draft 3rd edition." The connection between the differential and integral forms is only discussed at an intuitive (rather than a detailed) level, and a new approach to naming the pieces of gaussian surfaces and amperian loops makes talking about how to construct these surfaces much easier. Even though this chapter is optional, the concepts of line integrals and flux integrals are now more carefully developed in chapters E3 and E5 in the context of potential and current (respectively), where the application of these ideas is somewhat more concrete.

The introduction to waves now appears in unit Q. Chapter E18 on electromagnetic waves no longer requires this. This move also makes unit Q able to stand on its own without requiring that unit E precede it.

Other changes (particularly from the 2nd edition) are so numerous that a list similar to what we have presented for the other units would not be very helpful. Look instead at the table of contents and better yet, study the text of the unit itself in some detail to see all the differences. However, we will say that teaching this unit in draft form over the past few years has a been significantly better experience than with any of its previous incarnations.

UNIT Q

This unit has also been significantly revised from the 2nd edition. In addition to the overarching goals for the new edition, one of the most important goals for this unit was reorganizing the material on spins (gathering material scattered over the unit into one place) and breaking the old chapters Q5 and Q6 into more manageable pieces. We also wanted to move the material on waves from unit E to this unit so that it could stand more easily on its own.

In our teaching experience, complex numbers proved to be an annoying and unnecessary distraction for introductory students. Though most students claim to have seen complex numbers in high school, students had much more difficulty using complex numbers than the author imagined when writing chapter Q5 for the 2nd edition. Over the years since that edition, we have found ways to teach the basic material (even time evolution) without complex numbers.

With this in mind, here is a list of important changes for this unit:

- Chapter Q1 on waves now presents most of the material that was in chapter E15 in previous editions. (The material on the wave equation was eliminated as irrelevant for this unit.)
- New material on the Doppler Effect now appears in chapter Q1.
- Chapter Q2 more extensively discusses resonance as a phenomenon.
- Chapter Q6 on spins now collects all of the material on spin into one place, making the unit's treatment of spin more coherent.
- Appendix QA on complex numbers now contains a better introduction to complex numbers than was in chapter Q5 of the 2nd edition, as well as a series of applications. This appendix is actually organized in the form of a chapter that a professor can assign after chapter Q9. Though we don't recommend this chapter for first-year students, we do recommend including this as an assigned chapter in a sophomore-level Modern Physics course. Even so, we think that exploring the structure of quantum mechanics without complex numbers is pedagogically valuable even for more advanced students.
- Chapter Q8 on Quantum Weirdness (optional) provides an entirely new discussion of the EPR experiment, Bell's Theorem, and Schrodinger's Cat. While it is optional, students at Pomona found this to be a very exciting and engaging chapter.
- A new discussion of semiconductors now appears in chapter Q11. This section is optional, but was requested by several users.
- Everything beyond chapter Q11 is optional, though chapters Q13 and Q14 should be included or omitted together, and chapter Q15 requires both Q13 and Q14.

Adding this material to the unit required some deletions to keep the length and pace manageable. The most important deletions include:

- Atomic physics and selection rules. Students found this material (chapter Q9 in the 2nd edition) to be mostly a rehash of what they had learned in chemistry, and that edition did not present this material very well. We now consider other material more important.
- Solving the Schrodinger equation mathematically. Perhaps few will mourn this deletion, which proved to be difficult for students and too abstract to build any understanding of the equation. The focus is now on wavefunction sketching and using Schrosolver.
- The covalent bond. This material is important but works much better as a class activity than as a chapter section. A multi-part problem in chapter C12 now outlines such an activity.
- The semi-empirical binding energy formula. We found that students did not absorb the physical meaning of each term in this equation, and were unnecessarily distracted by the mathematics. The chapters on nuclear energy have therefore been reorganized and compressed to focus on more basic physical principles.

UNIT T

This unit covers most of the same material as in the 2nd edition, but its presentation has been significantly reorganized, both for clarity and for the sake of flexibility.

- Chapter T1 now includes a more historically accurate treatment of temperature, as well as some of the material appearing in T2 of the 2nd edition.
- Chapter T2 now goes directly into introducing the Einstein solid, instead of wandering off into a detour about ideal gases. It now provides a more streamlined treatment of material that appeared in chapters T4 and T5 of the 2nd edition.
- Chapter T3 now defines entropy and temperature, presenting a streamlined version of material that appeared in chapters T5 and T6 of the 2nd edition,
- Chapter T4 now focuses entirely on a more extensive treatment of the Boltzmann factor, which appeared as only part of chapter T6 in the 2nd edition. It also takes advantage of tools such as WolframAlpha that have appeared since that edition to offer a richer exploration of this topic.
- Chapter T5 uses the techniques introduced in chapter T4 to enable a different approach to the ideal gas that includes the kinetic-theory material in the old chapter T2, but provides a much more complete picture of monatomic and diatomic gases.
- Chapter T6 (optional) now discusses the Maxwell-Boltzmann distribution as well as offering new material on photon gases (the Planck distribution). This material is the most difficult in the unit and is now entirely optional: one can skip from chapter T5 to T7 without problems.
- Chapter T7 presents the material about ideal gas processes that was in the old chapter T3, but in a streamlined way that is more gently paced.
- Chapters T8 and T9 are mostly the same as before, except that T8 provides a more careful discussion of the entropy of ideal gases. Students may find the argument here a bit sophisticated, but equation T8.7 is what really matters.
- Chapter T10 provides a completely new discussion of the physics of climate change. It appears here because it involves thermal physics principles, provides a nice application of the Planck material in chapter T6, and can provide a thoughtful and compelling conclusion to a course (in the recommended sequence) that is ultimately about modeling, but in fact only crucially depends on chapter C13 and so could be presented any time after that chapter.

Besides grouping the material in a more organized way, this reorganization gives the professor more flexibility about what to include. Chapter T1-T3 now provide a complete treatment of the unit's main idea. Chapter T4 adds valuable material about the Boltzmann factor and T5 adds valuable material about ideal gases. One could therefore provide a very decent introduction to thermal physics with just these five chapters. One can even split unit T into two separated halves to better fit a given calendar.

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