SUPERSTRINGS AND OTHER THINGS AGUIDE TO P HYSICS About the Author Carlos I Calle received his PhD in theoretical nuclear physics from Ohio University. He is a senior research scientist at NASA Kennedy Space Center where he leads the electromagnetic physics research group. Dr Calle is currently working on the problem of electro- static phenomena on planetary surfaces, particularly on Mars and the Moon, developing instrumentation for future planetary exploration missions. He is the principal investigator for the electrostatic studies of Martian soil and dust and for the electrometer calibra- tion project for the Mars Surveyor mission. He is also project manager for the study of the electrostatic properties of lunar soil and dust. His earlier research work involved the development of a theoretical model for a microscopic treatment of particle scattering. He also introduced one-particle excitation operators in a separable particle-hole Hamiltonian for the calculation of particle excitations. As a professor of physics for many years, he taught the whole range of college physics courses. He has pub- lished over eighty scienti®c papers and been invited to participate in international scienti®c conferences. He has been the recipient of ten research grants from NSF, from NASA, and from private foundations. SUPERSTRINGS AND OTHER THINGS AGUIDE TO P HYSICS CARLOS ICALLE NASA Kennedy Space Center Institute of Physics Publishing Bristol and Philadelphia # IOP Publishing Ltd 2001 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publisher. Multiple copying is permitted in accordance with the terms of licences issued by the Copyright Licensing Agency under the terms of its agreement with the Committee of Vice- Chancellors and Principals. British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. ISBN 0 7503 0707 2 Library of Congress Cataloging-in-Publication Data are available Commissioning Editor: Nicki Dennis Production Editor: Simon Laurenson Production Control: Sarah Plenty Cover Design: Fre  de  rique Swist Marketing Executive: Laura Serratrice Published by Institute of Physics Publishing, wholly owned by The Institute of Physics, London Institute of Physics, Dirac House, Temple Back, Bristol BS1 6BE, UK US Of®ce: Institute of Physics Publishing, The Public Ledger Building, Suite 1035, 150 South Independence Mall West, Philadelphia, PA 19106, USA Typeset by Academic  Technical Typesetting, Bristol Printed in the UK by J W Arrowsmith Ltd, Bristol To Dr Luz Marina Calle, Fellow NASA Scientist and Wife and to our son Daniel CONTENTS PREFACE xv PART 1: INTRODUCTORY CONCEPTS 1 PHYSICS: THE FUNDAMENTAL SCIENCE 3 What is physics? 3 The scienti®c method: learning from our mistakes 7 Physics and other sciences 9 Sizes of things: measurement 13 Fundamental units 15 Physics and mathematics 18 Frontiers of physics: Very small numbers 19 Pioneers of physics: Measuring the circumference of the Earth 20 PART 2: THE LAWS OF MECHANICS 2 THE DESCRIPTION OF MOTION 25 Understanding motion 25 Uniform motion 26 Average speed 27 The frontiers of physics: Friction 29 Instantaneous speed 30 Velocity: Speed and direction 31 Vectors 31 Acceleration 34 Uniformly accelerated motion 35 Falling bodies 37 Pioneers of physics: Galileo's method 39 The motion of projectiles 40 vii 3THELAWSOFMECHANICS: NEWTON'S LAWS OF MOTION 43 The concept of force 43 The ancient idea of motion 44 The birth of modern science 45 Pioneers of physics: Galileo's dialog with Aristotle 47 Galileo formulates the Law of Inertia 48 Physics in our world: The Leaning Tower of Pisa 50 Newton's First Law: Law of inertia 52 Physics in our world: Car seat belt 54 Newton's Second Law: Law of force 56 Newton's Third Law: Law of action and reaction 59 4ENERGY 62 What is energy? 62 The concept of work 62 Units of work and energy 66 The concept of energy 66 Pioneers of Physics: James Prescott Joule (1818±1889) 67 The work-energy theorem 74 Conservative and nonconservative forces 75 5 CONSERVATION OF ENERGY AND MOMENTUM 78 Transformation of energy 78 The principle of conservation of energy 80 The energy of mass 81 Ef®ciency 82 Pioneers of physics: The physicists' letters 83 Power 85 Physics in our world: Automobile ef®ciency 86 Impulse and momentum 88 Physics in our world: Air bags 90 Conservation of momentum 91 Elastic and inelastic collisions 94 Cannons and rockets 95 6 ROTATION AND THE UNIVERSAL LAW OF GRAVITATION 98 Rotational motion 98 The frontiers of physics: CD-ROM drives 101 Torque and angular momentum 102 SUPERSTRINGS AND OTHER THINGS viii Physics in our world: Twisting cats 106 Centripetal acceleration 108 Satellites 110 Origins of our view of the universe 110 Kepler's laws of planetary motion 114 Newton's law of universal gravitation 118 The frontiers of physics: Measuring the distance to the Moon 124 Spacecraft and orbital motion 125 The frontiers of physics: The Global Positioning Satellite System 128 PART 3: THE STRUCTURE OF MATTER 7 ATOMS: BUILDING BLOCKS OF THE U N I V E R S E 133 The underlying structure of matter 133 The Atomic Hypothesis 133 Early concept of the atom 134 First models of the atom 136 Waves and quanta 141 The Bohr model of the atom 145 Molecules 147 Physics in our world: Winemaking 149 8 THE HEART OF THE ATOM: THE NUCLEUS 151 Raw material: Protons and neutrons 151 Pioneers of physics: Heisenberg's failing grade 152 The composition of the nucleus 153 The glue that keeps the nucleus together 155 Size and shape of the nucleus 159 Nuclear energy levels 161 9 F L U I D S 164 States of matter 164 Density 165 Pressure 166 Buoyancy 176 Surface tension and capillarity 179 Fluids in motion 184 The human cardiovascular system 186 Physics in our world: Curve balls 187 Contents ix PART 4: THERMODYNAMICS 10 HEAT AND TEMPERATURE 195 Heat as a form of energy 195 Pioneers of physics: Count Rumford 197 Measuring temperature 199 Temperature and heat 201 Physics in our world: Thermography 204 Heat capacity 205 Heat of fusion and heat of vaporization 207 Evaporation and boiling 210 Physics in our world: Instant ice cream 213 Humidity 213 Thermal expansion 215 The unusual expansion of water 218 11 T H E L A W S O F T H E R M O D Y N A M I C S 221 The four laws of thermodynamics 221 The ideal gas law 221 Physics in our world: Automobile engines 224 The zeroth law of thermodynamics 225 The ®rst law of thermodynamics 226 The second law of thermodynamics 229 The third law of thermodynamics 233 The frontiers of physics: Entropy that organizes? 234 Entropy and the origin of the Universe 235 Entropy and the arrow of time 239 PART 5: ELECTRICITY AND MAGNETISM 12 ELECTRICITY 247 Electromagnetism 247 Electric charge 248 Coulomb's law 250 The electric ®eld 253 The fundamental charge 256 The frontiers of physics: Electrostatics on Mars 258 Electric potential 260 Storing electrical energy 262 The frontiers of physics: Storing single electrons 264 Physics in our world: Inkjet printers 265 SUPERSTRINGS AND OTHER THINGS x [...]... trillion The 1967 General Conference on Weights and Measures 15 Figure 1.7 Range of masses, lengths and time intervals found in the universe SUPERSTRINGS AND OTHER THINGS 16 Physics: The Fundamental Science Figure 1.8 A cesium atomic clock at the National Institute of Standards and Technology in Washington, DC (Courtesy National Institute of Standards and Technology.) de®ned the second as the duration... designed for the National Bureau of Standards, allows the comparison of the masses of other bodies within a few parts in a billion 17 SUPERSTRINGS AND OTHER THINGS (Cartoon by Sydney Harris.) The mass of an atom cannot be measured by comparison with the standard kilogram with such a high degree of precision The masses of atoms, however, can be compared with each other with high accuracy For this reason,... scienti®c ®elds and of the way working scientists apply the scienti®c method to their work 9 SUPERSTRINGS AND OTHER THINGS In 1980, the Nobel prize winning physicist Luis Alvarez and his son Walter, a professor of geology at the University of California at Berkeley, reported in a paper published in the journal Science that some 65 million years ago a giant meteorite crashed into the earth and caused the... is interested in learning about physics It is also useful to scientists in other disciplines and to professionals in non-scienti®c ®elds The book takes the reader from the basic introductory concepts xv SUPERSTRINGS AND OTHER THINGS to discussions about the current theories about the structure of matter, the nature of time, and the beginning of the universe Since the book is conceptual, I have kept... offering criticism and advice every time Professor Kirby W Kemper at Florida State University, reviewed the book several times and suggested changes, corrections, and better ways to describe or explain a concept The book is better because of them Finally, I wish to thank Nicki Dennis, Simon Laurenson and Victoria Le Billon at IOP Publishing, and Graham Saxby, for their understanding and for their ef®ciency... the truth And this is how we learn from our mistakes.'' Physics and other sciences Physicists often become interested in phenomena normally studied by scientists in other scienti®c disciplines, and apply their knowledge of physics to these problems with great success The recent formulation of the impact theory of mass extinctions is a good illustration of physicists becoming involved in other scienti®c... atom and its nucleus The book continues with thermodynamics in Part 4, the conceptual development of electricity and magnetism in Part 5, waves and light (Part 6), and ®nally, in Part 7, with the rest of the story of modern physics, from the development of quantum theory and relativity to the present theories of the structure of matter Acknowledgments I wish to thank ®rst my wife, Dr Luz Marina Calle, ... during the thousand years that it took to form If that were the case, they could measure the amount of iridium in the clay and in the rocks above the clay (formed later) and below (formed earlier) and determine the time it had taken for the iridium to accumulate To that effect, they enlisted the help of Frank Asaro and Helen Michel, nuclear chemists at the Lawrence Berkeley Laboratory Asaro and Michel showed... clay layer contains three hundred times as much iridium as the layers above and below The source of this unusual amount of iridium had to be extraterrestrial, Luis Alvarez reasoned Meteorites, which are Figure 1.5 K-T boundary layer with a high concentration of iridium (Courtesy Alessandro Montanari.) 11 SUPERSTRINGS AND OTHER THINGS extraterrestrial, have fallen on the earth since its formation If the... Roman feet In the 15th century, Queen Bess of England added 280 feet to the mile to make it eight ``furrow-longs'' or furlongs In 1790, Thomas Jefferson proposed a system based on units of 10 where 10 feet would be a decad, 10 decads a road, 10 roads a furlong, and 10 furlongs a mile Congress did not approve Jefferson's system 13 SUPERSTRINGS AND OTHER THINGS Figure 1.6 The meter was originally de®ned