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Newtonian Physics

by Benjamin Crowell

Learning to Hate Physics?
When you read a mystery novel, you know in advance what structure to expect: a crime, some detective work, and finally the unmasking of the evildoer. Likewise when Charlie Parker plays a blues, your ear expects to hear certain landmarks of the form regardless of how wild some of his notes are. Surveys of physics students usually show that they have worse attitudes about the subject after instruction than before, and their comments often boil down to a complaint that the
person who strung the topics together had not learned what Agatha Christie and Charlie Parker knew intuitively about form and struc-ture: students become bored and demoralized because the “march through the topics” lacks a coherent story line. You are reading the first volume of the Light and Matter series of introductory physics textbooks, and as implied by its title, the story line of the series is built around light and matter: how they behave, how they are different from each other, and, at the end of the story, how they turn out to be similar in some very bizarre ways.
Here is a guide to the structure of the one-year course presented in this series:

1 Newtonian Physics Matter moves at constant speed in a straight line unless a force acts on it. (This seems intuitively wrong only because we tend to forget the role of friction forces.) Material objects can exert forces on each other, each changing the other’s motion. A more massive object changes its motion more slowly in
response to a given force.
2 Conservation Laws Newton’s matter-and-forces picture of the universe is fine as far as it goes, but it doesn’t apply to light, which is a form of pure energy without mass. A more powerful world-view, applying equally well to both light and matter, is pro-vided by the conservation laws, for instance the law of conservation of energy, which states that energy can never be destroyed or created but only changed from one form into another.
3 Vibrations and Waves Light is a wave. We learn how waves travel through space, pass through each other, speed up, slow down, and are reflected.
4 Electricity and Magnetism Matter is made out of particles such as electrons and protons, which are held together by electrical forces. Light is a wave that is made out of patterns of electric and magnetic force.
5 Optics Devices such as eyeglasses and searchlights use matter (lenses and mirrors) to manipulate light.
6 The Modern Revolution in Physics Until the twentieth century, physicists thought that matter was made out of particles and light was purely a wave phenomenon. We now know that both light and matter are made of building blocks with a combination of particle and wave properties. In the process of understanding this apparent contradiction, we find that the universe is a much stranger place than Newton had ever imagined, and also learn the basis for such devices as lasers and computer chips.

A Note to the Student Taking Calculus Concurrently
Learning calculus and physics concurrently is an excellent idea — it’s not a coincidence that the inventor of calculus, Isaac Newton, also discovered the laws of motion! If you are worried about taking these two demanding courses at the same time, let me reassure you.
I think you will find that physics helps you with calculus while cal-culus deepens and enhances your experience of physics. This book is designed to be used in either an algebra-based physics course or a calculus-based physics course that has calculus as a corequisite. This note is addressed to students in the latter type of course.
Art critics discuss paintings with each other, but when painters get together, they talk about brushes. Art needs both a “why” and a “how,” concepts as well as technique. Just as it is easier to enjoy an oil painting than to produce one, it is easier to understand the concepts of calculus than to learn the techniques of calculus.
This book will generally teach you the concepts of calculus a few weeks before you learn them in your math class, but it does not discuss the techniques of calculus at all. There will thus be a delay of a few weeks between the time when a calculus application is first pointed out in this book and the first occurrence of a homework problem that requires the relevant technique. The following outline shows a typical first-semester calculus curriculum side-by-side with
the list of topics covered in this book, to give you a rough idea of what calculus your physics instructor might expect you to know at a given point in the semester. The sequence of the calculus topics is the one followed by Calculus of a Single Variable, 2nd ed., by Swokowski, Olinick, and Pence.