Why This Book?

I find that the traditional introductory physics textbook can be difficult or even overwhelming to read and understand, and that is because it tries to present three different categories of information at once:

1. Concepts and Equations: These are the things you need to know: concepts like Newton's Laws, or the definition of acceleration, or Ohm's Law. The details about these subjects are fair game for exams, especially multiple-choice questions.
2. Problem-Solving: This is what you need to know how to do. The process is what's important here; the details are not.
3. History and Applications: These serve to motivate you, and to help you to connect physics to other fields. They are interesting and may provide context, but you probably won't be tested on them.

Ideally, these should be three separate books:

1. A textbook to be read before class and maybe quizzed on
2. A workbook, or maybe a series of groupwork worksheets, accompanied by examples worked out in the classroom
3. A cozy non-fiction book that you can read a night, with a good narrative and minimal mathematics.

How Things Move, Why Things Move is my attempt at Book 1. It focuses on the essential concepts of physics, leaving the problem-solving and applications to be covered by other sources. This makes the book shorter, and it's easier to say "Read Chapter 1 for Monday, and yes you do need to know everything in the chapter." I have tried to make the book easier to read than the traditional physics book, with one topic per page to avoid the "wall of text" effect that a traditional textbook can provide. And the book is online and free to use, so that students are not financially constrained from reading it.

The book follows a fairly standard sequence of a two-semester algebra-based introductory course in physics, with two exceptions:

• The book starts with forces before kinematics. In my experience, kinematics involve the hardest mathematics in the course, very algebra-heavy, and set the tone of the physics course as being "applied math". By starting with forces and specifically static equilibrium, we start with much simpler math: "these forces balance those forces". Forces serve as a more natural introduction to vectors, and when we do get to kinematics we can use constant force as a motivation for discussing constant-acceleration problems.
• The book discusses electric potential before the electric field. We use the common metaphor of "potential as altitude", and this scalar field is easier to intuit at first than a vector field. (Vector fields can also be inferred to refer to motion.) Students are more likely to be aware of voltage, and electric potential leads naturally into current and circuits, so that circuit labs can start earlier in the semester. After circuits, the book introduces electric field as "a vector that points downhill at every location", and that chapter is immediately followed by one on the magnetic field, do that similarities (such as the dipole field) are more readily apparent.

If you have questions or suggestions, please feel free to contact me at textbook@sahill.us. Thank you!

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:@-) Sam
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