Springer UNDERSTANDING PHYSICS. Series Editors John P. Ertel Robert C. Hilborn David Peak Thomas Rossing Cindy Schwarz

Transcription

1 UNDERSTANDING PHYSICS Series Editors John P. Ertel Robert C. Hilborn David Peak Thomas Rossing Cindy Schwarz Springer New York Berlin Heidelberg Hong Kong London Milan Paris Tokyo

2 UNDERGRADUATE TEXTS IN CONTEMPORARY PHYSICS Cassidy, Holton, and Rutherford, Understanding Physics Enns and McGuire, Computer Algebra Recipes: A Gourmet s Guide to the Mathematical Models of Science Hassani, Mathematical Methods: For Students of Physics and Related Fields Holbrow, Lloyd, and Amato, Modern Introductory Physics Roe, Probability and Statistics in Experimental Physics, Second Edition Rossing and Chiaverina, Light Science: Physics and the Visual Arts

3 UNDERSTANDING PHYSICS David Cassidy Gerald Holton James Rutherford With 571 Illustrations, with 6 in Full Color 123

4 David Cassidy Gerald Holton Professor of Natural Science Mallinckrodt Professor of Physics and History Natural Science Program of Science, Emeritus Hofstra University 358 Jefferson Physical Laboratory Hempstead, NY Harvard University USA Cambridge, MA USA James Rutherford Education Advisor American Association for Advancement of Science Washington, DC USA Series Editors John P. Ertel Robert C. Hilborn Cindy Schwarz Department of Physics Department of Physics Department of Physics and United States Naval Academy Amherst College Astronomy 572 Holloway Road Amherst, MA Vassar College Annapolis, MD USA Poughkeepsie, NY USA USA David Peak Thomas Rossing Department of Physics Department of Physics Utah State University Northern Illinois University Logan, UT De Kalb, IL USA USA Library of Congress Cataloging-in-Publication Data Cassidy, David C., 1945 Understanding physics / David Cassidy, Gerald Holton, F. James Rutherford. p. cm. (Undergraduate texts in contemporary physics) Rev. ed. of: The project physics course Includes bibliographical references and index. ISBN (pbk. : acid-free paper) 1. Physics. I. Holton, Gerald James. II. Rutherford, F. James (Floyd James), 1924 III. Harvard Project Physics. Project physics course. IV. Title. V. Series. QC23.2.C dc ISBN Printed on acid-free paper Springer-Verlag New York, Inc. All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer-Verlag New York, Inc., 175 Fifth Avenue, New York, NY 10010, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. Printed in the United States of America SPIN Springer-Verlag New York Berlin Heidelberg A member of BertelsmannSpringer Science Business Media GmbH

5 To the students and instructors whose advice, while using the draft versions of the text and guides, helped to improve our work greatly; and to Joan Laws, whose quiet expertise all these years helped to bring the project to success.

6 Science is an adventure of the whole human race to learn to live in and perhaps to love the universe in which they are. To be a part of it is to understand, to understand oneself, to begin to feel that there is a capacity within man far beyond what he felt he had, of an infinite extension of human possibilities.... I propose that science be taught at whatever level, from the lowest to the highest, in the humanistic way. It should be taught with a certain historical understanding, with a certain philosophical understanding, with a social understanding and a human understanding in the sense of the biography, the nature of the people who made this construction, the triumphs, the trials, the tribulations. I.I. Rabi, Nobel Laureate in Physics

7 Preface Understanding Physics is a completely revised, updated, and expanded edition of the Project Physics Course. It is an integrated introductory physics course, developed with funding from the Carnegie Corporation and the Sloan Foundation and with the close cooperation of Springer-Verlag New York. In approach and content, Understanding Physics follows the trail blazed by the earlier versions, but it includes more recent developments in physics and a stronger emphasis on the relationships among physics, technology, and society. We have sought especially to incorporate the salient lessons of recent physics education research and practical experience gained in the classroom. The Audience Understanding Physics is written primarily for undergraduate college students not intending (at least initially) to enter careers in science or engineering. These may include liberal-arts students, business majors, prelegal, and prospective architecture students. We have found that when the course is taken with laboratory work, it has been deemed suitable by medical schools for premedical students. An important group that this course is intended to serve are persons who plan to teach, or are already teaching, in K 12 classrooms. As has been widely discussed, there is a special need for improvement in the science education of current and future teachers as an important step toward achieving greater scientific literacy in general. Many states have recently incorporated the contextual approach used in Understanding Physics into state science education criteria. It is in part to meet the challenges of teacher education that this course was developed as a resource, along with the usual pedagogical training. Since college students in introductory science courses usually represent a wide spectrum of expertise in science and mathematics, this book assumes ix

8 x PREFACE no prerequisites in science or mathematics beyond high-school algebra, geometry, and general science. In this text we have taken great care to derive all necessary equations very patiently, but whenever possible we have used narrative text instead of equations to convey the meanings of laws and concepts. Even if students have taken physics in high school, they often still lack proficiency in even the most basic concepts and techniques. One of the aims of this course is to enable all students to gain experience and confidence with physical-science concepts and quantitative methods, and with an understanding of the nature of science itself. Of course, for classes in which the students are sufficiently prepared, instructors may decide to place more emphasis on quantitative or other aspects of physics as appropriate. The course is designed with such flexibility in mind. The Approach A unique feature of this text, like its predecessor, is that it places the fundamental concepts of physics within the broader humanistic and historical contexts in which they arose, but without handicapping students in tests that compare their performance with students who have taken a less broadly conceived, conventional physics course. Research has shown that students exposed to our approach gain a much deeper understanding of both the content and the processes of scientific research, as well as an appreciation not only of what we know, but also of how and why we think we know it. This approach has been endorsed by several national organizations, including the National Science Foundation, the Research Council of the National Academy of Sciences, and Project 2061 of the American Association for the Advancement of Science. The National Research Council stated in its National Science Education Standards:* In learning science, students need to understand that science reflects its history and is an ongoing, changing enterprise. The standards for the history and nature of science recommend the use of history in school science programs to clarify different aspects of scientific inquiry, the human aspects of science, and the role that science has played in the development of various cultures. Thus, Understanding Physics operates on two levels, providing both the fundamental concepts of physics and the humanistic and intellectual contexts in which the concepts developed. In addition to the necessary concepts and equations, intentionally developed patiently, and using easy-tovisualize examples, it aims to convey a real sense of the nature of scientific * Washington, DC: National Academy Press, 1996; p. 107.

9 PREFACE xi thinking, the way intuitions about science had to be, often painfully, acquired by scientists, and what our current concepts really mean. However, this text is not intended to be used by itself, but rather as part of a program as integrated as possible with hands-on activities, small-group discussions either in or out of class, and other encouragements to active learning that enable the subject matter to come alive. Some of these and other possible activities are suggested in the accompanying Student Guide. Understanding Physics is divided into two parts. Each part is selfcontained, with enough material for a course lasting at least one semester. Each part encompasses topics in classical physics along with one of the two contemporary nonclassical physics: relativity theory and quantum mechanics. Both parts taken together may serve for a full one-year course. We have sought from the beginning to provide instructors with maximum flexibility in adapting the course to students of different backgrounds, to different educational settings, to different semester time frames, and to different preferences for course topics. Some suggestions for different scenarios are provided in the accompanying Instructor Guide. All of the course s printed materials, as well as links to many related Web sites for both instructors and students, may also be accessed on the World Wide Web via the publisher s site at Acknowledgments We are grateful to the Carnegie Corporation of New York and to the Sloan Foundation for their generous and timely support. Thomas von Foerster and the staff of Springer-Verlag New York provided much-appreciated encouragement, support, and helpful advice during the years of preparation and testing of these materials in draft form. We also thank David Couzens, our developmental editor, whose outstanding work on the illustrations and his suggestions regarding the content contributed greatly to this work, and Edwin F. Taylor for his very helpful comments regarding the chapter on relativity theory. We are indebted to our colleagues at Hofstra University and to the other instructors who thoroughly tested the draft of the text and guides in their classes, and offered many helpful comments and suggestions. We also thank our colleagues and the individuals who carefully reviewed the materials and provided insightful suggestions. Last but not least, we thank the students at all testing sites for their valuable suggestions and encouragement. Without the contributions of all of these individuals and institutions, this work would not have been possible. David Cassidy Gerald Holton James Rutherford

10 Brief Contents Preface ix PART ONE: MATTER AND MOTION Prologue to Part One 3 1 Motion Matters 15 2 Moving the Earth 57 3 Understanding Motion Newton s Unified Theory Conserving Matter and Motion The Dynamics of Heat Heat: A Matter of Motion Wave Motion Einstein and Relativity Theory 405 PART TWO: FIELDS AND ATOMS Prologue to Part Two Electricity and Magnetism The Electric Age Electromagnetic Waves Probing the Atom The Quantum Model of the Atom Quantum Mechanics Solids Matter Probing the Nucleus The Nucleus and Its Applications 763 Illustration Credits 819 Index 829 xiii

11 Contents Preface ix PART ONE: MATTER AND MOTION PROLOGUE TO PART ONE 3 1 Living Ideas 3 2 Our Place in Time and Space 4 3 First Things First 6 4 Aristotle s Universe 9 CHAPTER 1. MOTION MATTERS Motion Galileo A Moving Object Picturing Motion Speed and Velocity Changing the Speed Falling Freely Two New Sciences Falling Objects The Consequences 47 xv

12 xvi CONTENTS CHAPTER 2. MOVING THE EARTH Astronomy, Motion, and Mechanics The Scientific Revolution Copernicus The Geocentric View Copernicus versus Ptolemy Arguments for the Heliocentric System Arguments against the Heliocentric System Carrying Forth the Revolution New Data New Orbits New Observations Galileo Condemned 109 CHAPTER 3. UNDERSTANDING MOTION 117 A. THE THREE LAWS OF MOTION Natural Motion and Newton s First Law Forces in Equilibrium More about Vectors Newton s Second Law of Motion Measuring Mass and Force More about Weight, and Weightlessness Newton s Third Law of Motion 140 B. THE THREE LAWS IN ACTION Projectile Motion The Earth Can Move! Galilean Relativity Orbiting Satellites Circular Motion 156

13 CONTENTS xvii CHAPTER 4. NEWTON S UNIFIED THEORY Newton and Seventeenth-Century Science Isaac Newton Newton s Principia The Inverse-Square Law The Law of Universal Gravitation Newton s Syntheses Newton and Hypotheses The Magnitude of the Gravitational Force The Value of G, and Some Consequences Further Successes The Nature of Newton s Work 204 CHAPTER 5. CONSERVING MATTER AND MOTION Conservation of Mass Collisions Conservation of Momentum Momentum and Newton s Laws of Motion Isolated Systems Elastic Collisions Leibniz and the Conservation Law Work Work and Kinetic Energy Potential Energy Conservation of Mechanical Energy Forces that Do No Work 243 CHAPTER 6. THE DYNAMICS OF HEAT Heat as a Form of Energy The Steam Engine and the Industrial Revolution Power and Efficiency of Engines 267

14 xviii CONTENTS 6.4 Carnot and the Beginnings of Thermodynamics Arriving at a General Conservation Law The Two Laws of Thermodynamics Faith in the Laws of Thermodynamics 282 CHAPTER 7. HEAT: A MATTER OF MOTION 293 A. THE KINETIC THEORY An Ideal Gas A Model for the Gaseous State The Speeds of Molecules The Sizes of Molecules 305 B. APPLYING THE KINETIC THEORY Kinetic-Theory Explanation of the Ideal Gas Law Kinetic-Theory Explanation of the Second Law Maxwell s Demon and the Statistical View of the Second Law Two Challenges 319 CHAPTER 8. WAVE MOTION 331 A. WAVES What Is a Wave? The Properties of Waves Wave Propagation Periodic Waves When Waves Meet A Two-Source Interference Pattern Standing Waves Wave Fronts and Diffraction Reflection Refraction Sound Waves 370

15 CONTENTS xix B. LIGHT What Is Light? Propagation of Light Reflection and Refraction Interference and Diffraction What Is Color? Why Is the Sky Blue? Polarization The Ether 395 CHAPTER 9. EINSTEIN AND RELATIVITY THEORY The New Physics Albert Einstein The Relativity Principle Constancy of the Speed of Light Simultaneous Events Relativity of Time Time Dilation Relativity of Length Relativity of Mass Mass and Energy Confirming Relativity Breaking with the Past 441 PART TWO: FIELDS AND ATOMS PROLOGUE TO PART TWO A Revolution in Science The Mechanical World View Energy and Atoms 455

16 xx CONTENTS CHAPTER 10. ELECTRICITY AND MAGNETISM Gilbert s Magnets Electric Charges and Electric Forces Forces and Fields Electric Currents Electric Potential Difference Electric Potential Difference and Current Electric Potential Difference and Power Currents Act on Magnets Currents Act on Currents Magnetic Fields and Moving Charges 495 CHAPTER 11. THE ELECTRIC AGE Transporting Energy from One Place to Another Faraday s First Electric Motor The Discovery of Electromagnetic Induction Generating Electricity: The Generator Putting Electricity to Work: The Motor The Electric Light Bulb AC versus DC: The Niagara Falls Power Plant The Energy Picture Today Conservation Renewable and Alternative Energy Sources 537 CHAPTER 12. ELECTROMAGNETIC WAVES Faraday s Suggestion Maxwell s Principles of Electromagnetism The Propagation of Electromagnetic Waves Hertz s Experimental Confirmation The Electromagnetic Spectrum What About the Ether Now? 578

17 CONTENTS xxi CHAPTER 13. PROBING THE ATOM The Periodic Table The Idea of Atomic Structure Cathode Rays The Smallest Charge Thomson s Model of the Atom The Photoelectric Effect Einstein s Theory of the Photoelectric Effect X Rays 608 CHAPTER 14. THE QUANTUM MODEL OF THE ATOM Spectra of Gases Regularities in the Hydrogen Spectrum Rutherford s Nuclear Model of the Atom Nuclear Charge and Size Bohr s Theory: The Postulates The Size of the Hydrogen Atom Other Consequences of the Bohr Model Bohr Accounts for the Series Spectra of Hydrogen Do Stationary States Really Exist? Constructing the Periodic Table Evaluating the Bohr Model 654 CHAPTER 15. QUANTUM MECHANICS The Quantum The Particle-Like Behavior of Light The Wave-Like Behavior of Particles Constructing Quantum Mechanics The Uncertainty Principle Origins and a Consequence of the Uncertainty Principle The Probability Interpretation 679

18 xxii CONTENTS 15.8 The Complementarity Principle Some Reactions 685 CHAPTER 16. SOLIDS MATTER The Success of Quantum Mechanics Forming a Solid Quantum Solids Conducting Electrons Banding Together Superconductors Semiconductors Introducing Impurities Semiconductor Devices Transistors Some Applications of Transistors 717 CHAPTER 17. PROBING THE NUCLEUS Questions about the Nucleus Becquerel s Discovery The Curies Discover Other Radioactive Elements Identifying the Rays The Charge and Mass of the Rays Rutherford s Mousetrap Radioactive Transformations Radioactive Decay Series Decay Rate and Half-Life The Concept of Isotopes Transformation Rules Summary of Notation for Nuclides and Nuclear Reactions Some Useful Applications of Radioactivity 753

19 CONTENTS xxiii CHAPTER 18. THE NUCLEUS AND ITS APPLICATIONS The Problem of Nuclear Structure The Proton Electron Hypothesis The Discovery of Artificial Transmutation The Discovery of the Neutron The Proton Neutron Model The Neutrino The Need for Particle Accelerators The Energy of Nuclear Binding Nuclear Binding Energy and Stability Nuclear Fission: Discovery Controlling Chain Reactions Nuclear Power Plants Nuclear Weapons Nuclear Fusion 805 Illustration Credits 819 Index 829