Preface
These notes are written to introduce you to physics under the assumption that you don’t know the subject. I hope you are going to learn some of the intellectual structure of physics and not just a collection of facts. I would 1ike you to end up with a sense of what physics is about, how it is devised, and how it forms a distinctive mode of thought – a particular way of looking at things.
To ease the path to understanding, I have kept the level of mathematics low. First-year, high-school algebra and a little geometry are all that you need. But although the level is low, the use of calculation, powers of ten, graphs, ratios and proportions, and simple algebraic manipulation are frequent. Physics is a quantitative way of looking at nature. Any attempt to evade that fact is de- ception. Without mathematics physics becomes a “gee-whiz!” spectator sport; I hope that in however limited a way you will be a participant rather than a spectator.
It is easier to participate if the game is interesting and if it is not so complicated and grandiose as to be incomprehensible. Consequently, these notes do not present the material of a traditional course of introductory physics. Instead they treat a few topics relevant to answering the fascinating questions: How might we live off our native planet in outer space? and What is it like there? To this end the notes discuss weightlessness, rotating structures, rocket propulsion, the basic features of energy in space, orbiting planets and satellites, enough rudiments of electricity and magnetism to understand some of the behavior of charged particles in space and the nuclear physics of solar energy.
Two warnings are necessary. First, the unifying theme of living in space with its intimations of science fiction should not build false expectations. To really understand the basic physics of living in orbit you need to work through a good deal of material fairly remote from “Star Wars,” and so we will. Furthermore, although we use material from the NASA sponsored study Space Settlements: A Design Study, you will not walk away from these notes prepared to build a space colony. In fact you may have some sober appreciaiton of the scope of such an undertaking and the daunting size of some of the problems.
The other warning is that these notes will leave enormous gaps in your acquain- tance with physics. Traditional teachers of physics will reel with horror at what I have left out. The simple harmonic oscillator is never mentioned; there is no optics at all; angular momentum is evaded at every turn; the second law of thermodynamics is not discussed; the treatment of electricity and magnetism is very limited and specialized to our interests here. There are other omissions too brutal to mention.
My hope is that by limiting the scope of physics presented here I will give you time to master a few rudiments well enough for you to experience the pleasures of applying them and reasoning and analyzing in the ways a physicist does. In order to make clearer what are these ways peculiar to physicists, these notes try to give you some idea of the differences between a fundamental physical law and an empirical law, and they compare physics with engineering to help you better distinguish pure science from technology. Thus if all goes well you should emerge from this course with a knowledge of some physics and an appreciation of some of the problems of engineering 1arge habitats in space. But most of a11 I hope you wi11 have a sense of the ways in which physics and engineering are enjoyable human activities. And I especially hope that you will have come to see physics as a human creation and that you will be inoculated against the stifling awe or terror that causes conversations with otherwise perfectly normal people to collapse into silence when I answer the question “What do you teach?” with the apparently chilling reply . . . “Physics.”