HOW THINGS WORK T H E P H Y S I C S O F E V E R Y D AY L I F E SIXTH EDITION LOUIS A.com 6 TH EDITION How Things Work THE PHYSICS OF EVERYDAY LIFE Louis A. Bloomfield The University of Virginia www.com To Karen for being such a wonderful friend and companion, to Aaron, Elana, and Rich for being everything a father could want, to Max and Rosie for being so cheerful and attentive, and to the students of the University of Virginia for making teaching, research, and writing fun. VP & DIRECTOR: Petra Recter EXECUTIVE EDITOR: Jessica Fiorillo DEVELOPMENT EDITOR: Jennifer Yee ASSISTANT DEVELOPMENT EDITOR: Mallory Fryc EXECUTIVE MARKETING MANAGER: Christine Kushner ASSOCIATE DIRECTOR, PRODUCT DELIVERY: Kevin Holm SENIOR PRODUCTION EDITOR: Sandra Dumas PRODUCT DESIGNER: Geraldine Osnato SENIOR PHOTO EDITOR: Billy Ray DESIGN DIRECTOR: Harry Nolan COVER AND TEXT DESIGNER: Thomas Nery This book was set in 10/12 Times Roman by Aptara Corporation. Book and cover were printed and bound by Quad Graphics/Versailles.
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Outside of the United States, please contact your local representative. Library of Congress Cataloging-in-Publication Data Names: Bloomfield, Louis, author. Title: How things work : the physics of everyday life / Louis A. Bloomfield, The University of Virginia.
Description: Sixth edition. | Hoboken, NJ : John Wiley & Sons, Inc. Identifiers: LCCN 2015033708| ISBN 9781119013846 (loose-leaf : alk. paper) | ISBN 1119013844 (loose-leaf: alk.
paper) Subjects: LCSH: Physics—Textbooks. Classification: LCC QC21.B56 2015 | DDC 530—dc23 LC record available at http://lccn.gov/2015033708 ISBN 978-1119-01384-6 (Binder Version) The inside back cover will contain printing identification and country of origin if omitted from this page. In addition, if the ISBN on the back cover differs from the ISBN on this page, the one on the back cover is correct. Printed in the United States of America 10 9 8 7 6 5 4 3 2 1 www.com Foreword I n today’s world we are surrounded by science and by I have been using this book in my classes for several the technology that has grown out of that science.
For years, and I continue to be impressed with how Lou can most of us, this is making the world increasingly mys- take seemingly highly complex devices and strip away terious and somewhat ominous as technology becomes the complexity to show how at their heart are simple ever more powerful. For instance, we are confronted by physics ideas. Once these ideas are understood, they can many global environmental questions such as the dan- be used to understand the behavior of many devices we gers of greenhouse gases and the best choices of energy encounter in our daily lives, and often even fix things that sources. These are questions that are fundamentally tech- before had seemed impossibly complex.
In the process of nical in nature and there is a bewildering variety of claims teaching from this book, I have increased my own under- and counterclaims as to what is “the truth” on these and standing of the physics behind much of the world around similar important scientific issues. For many people, the me. In fact, after consulting How Things Work, I have had reaction is to throw up their hands in hopeless frustration the confidence to confront both plumbers and aircondi- and accept that the modern world is impossible to under- tioner repairmen to tell them (correctly as it turned out) stand and one can only huddle in helpless ignorance at the that their diagnosis did not make sense and they needed to mercy of its mysterious and inexplicable behavior. do something different to solve my plumbing and AC In fact, much of the world around us and the technol- problems.
Now I am regularly amused at the misconcep- ogy of our everyday lives is governed by a few basic tions some trained physicists have about some of the physics principles, and once these principles are under- physics they encounter in their daily lives, such as how a stood, the world and the vast array of technology in our microwave oven works and why it can be made out of lives become understandable and predictable. How does metal walls, but putting aluminum foil in it is bad. It has your microwave oven heat up food? Why is your radio convinced me that we need to take the approach used in reception bad in some places and not others? And why this book in far more of our science texts. can birds happily land on a high-voltage electrical wire? Of course, the most important impact is on the stu- The answers to questions like these are obvious once you dents in my classes that use this book.
These are typically know the relevant physics. Unfortunately, you are not nonscience students majoring in fields such as film likely to learn that from a standard physics course or studies, classics, English, business, etc. They often come physics textbook. There is a large body of research show- to physics with considerable trepidation.
It is inspiring to ing that, instead of providing this improved understanding of see many of them discover to their surprise that physics is everyday life, most introductory physics courses are very different from what they thought—that physics can doing quite the opposite. In spite of the best intentions of actually be interesting and useful and makes the world a the teachers, most students are “learning” that physics is much less mysterious and more understandable place. I abstract, uninteresting, and unrelated to the world around remember many examples of seeing this in action: the them. student who, after learning how both speakers and TVs How Things Work is a dramatic step toward changing work, was suddenly able to understand that it was not that by presenting physics in a new way.
Instead of start- magic that putting his large speaker next to the TV dis- ing out with abstract principles that leave the reader with torted the picture but in fact it was just physics, and now the idea that physics is about artificial and uninteresting he knew just how to fix it; the young woman scuba diver ideas, Lou Bloomfield starts out talking about real objects who, after learning about light and color, suddenly interrupted and devices that we encounter in our everyday lives. He class to announce that now she understood why it was then shows how these seemingly magical devices can be that you could tell how deep you were by seeing what understood in terms of the basic physics principles that color lobsters appeared; or the students who announced govern their behavior. This is much the way that most that suddenly it made sense that the showers on the first physics was discovered in the first place: people asked floor of the dorm worked better than those on the second why the world around them behaved as it did and as a floor. In addition, of course everyone is excited to learn result discovered the principles that explained and pre- how a microwave oven works and why there are these dicted what they observed.
strange rules as to what you can and cannot put in it.com vi Foreword These examples are particularly inspiring to a teacher, book an interesting and enlightening read and will go because they tell you that the students are not just learn- away comforted in that the world is not so strange and ing the material presented in class but they are then able inexplicable after all. to apply that understanding to new situations in a useful way, something that happens far too seldom in science Carl Wieman courses. Nobel Laureate in Physics 2001 Whether a curious layperson, a trained physicist, or a CASE/Carnegie US University Professor beginning physics student, most everyone will find this www.com Contents CHAPTER 1 TH E L AW S OF M OTI ON, PART 1 1 Active Learning Experiment: Removing a Tablecloth from a Table 1 Chapter Itinerary 2 1.3 Ramps 21 (support forces, Newton’s third law, energy, work, conservation of energy, kinetic and potential energies, gravitational potential energy, ramps, mechanical advantage) Epilogue for Chapter 1 31 / Explanation: Removing a Tablecloth from a Table 31 / Chapter Summary and Important Laws and Equations 31 CHAPTER 2 T H E L AW S OF M OTI ON, PART 2 33 Active Learning Experiment: A Spinning Pie Dish 33 Chapter Itinerary 34 2.3 Bumper Cars 59 (momentum, impulse, conservation of momentum, angular momentum, angular impulse, conservation of angular momentum, gradients, potential energy, acceleration, and forces) Epilogue for Chapter 2 70 / Explanation: A Spinning Pie Dish 70 / Chapter Summary and Important Laws and Equations 70 vii www.com viii Content CHAPTER 3 ME C HANI CAL OBJ ECTS PART 1 72 Active Learning Experiment: Swinging Water Overhead 72 Chapter Itinerary 73 3.2 Ball Sports: Bouncing 79 (collisions, energy transfers, elastic and inelastic collisions, vibration) 3.3 Carousels and Roller Coasters 86 (uniform circular motion, feeling of acceleration, apparent weight, centripetal acceleration) Epilogue for Chapter 3 94 / Explanation: Swinging Water Overhead 94 / Chapter Summary and Important Laws and Equations 95 CHAPTER 4 ME C HANI CAL OBJ ECTS PART 2 96 Active Learning Experiment: High-Flying Balls 96 Chapter Itinerary 97 4.2 Rockets and Space Travel 104 (reaction forces, law of universal gravitation, elliptical orbits, escape velocity, Kepler’s laws, speed of light, special and general relativity, equivalence principle) Epilogue for Chapter 4 117 / Explanation: High-Flying Balls 117 / Chapter Summary and Important Laws and Equations 117 CHAPTER 5 FL U ID S 119 Active Learning Experiment: A Cartesian Diver 119 Chapter Itinerary 120 5.2 Water Distribution 131 (hydrostatics, Pascal’s principle, hydraulics, hydrodynamics, steady state flow, streamlines, pressure potential energy, Bernoulli’s equation) Epilogue for Chapter 5 140 / Explanation: A Cartesian Diver 140 / Chapter Summary and Important Laws and Equations 141 www.com Content ix CHAPTER 6 FL UI D S AND M OTI ON 142 Active Learning Experiment: A Vortex Cannon 142 Chapter Itinerary 143 6.