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?≥ √> Ω+ π cm ? ≈≤ < =="" brainteaser="" physics="" 1="AB" ω=""> This page intentionally left blank ? ≥ Ω √ < π="" m="" c="" ≈="" ≤="" brainteaser="" ω="" π="" 1="" physics="" ab=""> Ω= Challenging cm √ Physics Puzzlers Göran Grimvall The Johns Hopkins University Press Baltimore © 2007 The Johns Hopkins University Press All rights reserved. Published 2007 Printed in the United States of America on acid-free paper 987654321 The Johns Hopkins University Press 2715 North Charles Street Baltimore, Maryland 21218-4363 www.press.jhu.edu Library of Congress Cataloging-in-Publication Data Grimvall, Göran. Brainteaser physics: challenging physics puzzlers / Göran Grimvall. p. cm. Includes bibliographical references and index. ISBN-13: 978-0-8018-8511-2 (acid-free paper) ISBN-10: 0-8018-8511-6 (acid-free paper) ISBN-13: 978-0-8018-8512-9 (pbk. : acid-free paper) ISBN-10: 0-8018-8512-4 (pbk. : acid-free paper) 1. Physics—Miscellanea. I. Title. QC75.G75 2007 530—dc22 2006025675 A catalog record for this book is available from the British Library. ?≥ √> Ω+ π cm ? ≈≤ < =="" contents="" 1="AB" ω=""> vii 1 Ten Hits 1 Dinghy in Pool / Ice in Water / Accident in Aqueduct / Floating Candle / Running in the Rain / Reaching Out / Resistor Cube / One, Two, Three, Infinity / Lost Energy / Simple Timetable / problems solutions 2 No Math Required 31 Moving Backward? / Heating Water / Bright Lamps? / Low Pressure / Site for Harbor / More Gas? / High Tension / Ocean Surface / Mariotte’s Bottle / problems solutions 3 Are You Sure? 55 Bicycle on a Rope / Boats in a Lock / Humming Transformer / What Is the Charge? / Two Wooden Blocks / Shot in a Pot / Filling a Barrel / Tube with Sand / Sauna Energy / Slapstick / problems solutions 4 Forces and Currents 79 Separated Boxes / Dropped Books / The Egg of Columbus / Helium or Hydrogen in the Balloon? / Lightbulb Found in a Drugstore? / Bright or Dark? / Yin and Yang / Rise and Fall of a Ball / Elevator Accident / problems solutions 5 Not Exact but Still Relevant 108 What Is Your Volume? / On the Move / Shot Put and Pole Vault / Record Stadium / Grains of Sand / Cooling Coffee / Time for Contact / Socrates’ Blood / problems solutions 6 Challenges for Your Creativity 127 Iron Bars / Faulty Balance / Greek Geometry / The Sugar Box / The Catenary / False Impressions / Testing the Hammer / Which Way? / Three Switches / Pulse Beats / Fake Energy Statistics / problems solutions Coda 146 Further Reading Index 157 vi contents 149 ?≥ √> Ω+ π cm ? ≈≤ < =="" preface="" 1="AB" ω="Solving" problems="" and="" coping="" with="" challenges="" are="" human="" traits.="" many="" of="" us="" do="" these="" things="" just="" for="" fun.="" crosswords="" and="" chess="" problems="" are="" found="" virtually="" everywhere.="" recreational="" mathematics="" problems="" is="" a="" genre="" with="" a="" vast="" literature.="" much="" less="" common="" are="" recreational="" physics="" problems—the="" theme="" of="" this="" book.="" here="" i="" present="" 57="" problems.="" some="" of="" them="" are="" well="" known="" in="" the="" popular="" scientific="" literature.="" others="" are="" classics="" that="" have="" been="" treated="" in="" the="" pedagogical="" physics="" literature.="" references="" to="" such="" works="" are="" given="" at="" the="" end="" of="" the="" book.="" most="" of="" the="" problems="" have="" appeared="" in="" shorter="" versions="" in="" my="" weekly="" column,="" which="" has="" been="" running="" for="" more="" than="" 27="" years="" in="" a="" swedish="" journal="" for="" engineers.="" i="" am="" presenting="" them="" now="" for="" the="" first="" time="" for="" an="" international="" audience.="" i="" don’t="" claim="" originality="" for="