The Physics of Rugby
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INTRODUCT I ON THE PHYSICS OF RUGBY i THE PHYS I CS OF RUGBY Nottingham University Press Manor Farm, Main Street, Thrumpton Nottingham, NG11 0AX, United Kingdom www.nup.com NOTTINGHAM First published 2009 © Trevor Davis Lipscombe All rights reserved. No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988. Applications for the copyright holder’s written permission to reproduce any part of this publication should be addressed to the publishers. British Library Cataloguing in Publication Data The Physics of Rugby TD Lipscombe ISBN 978-1-904761-17-4 Cover photo by Jusben (www.morguefile.com) Typeset by Nottingham University Press, Nottingham Cert no. SA-COC-1530 Printed and bound by Hobbs the Printers, Hampshire, England ii INTRODUCT I ON The Physics of Rugby Trevor Davis Lipscombe iii THE PHYS I CS OF RUGBY iv INTRODUCT I ON TABLE OF CON T EN T S Introduction vii Chapter One Pack Animals: On scrums, lineouts, rucks, and mauls 1 Chapter Two Back Attack: On running, passing, and scoring 29 in the corner Chapter Three Crunch time: On chasing, tackling, and injuries 63 Chapter Four Kicking, the habit: On penalties, conversions, 95 and Garryowens Chapter Five Match Day: On the weather you’ll play in and 131 whether you’ll win Suggested further reading 161 Glossary of physics terms 167 Index of rugby players 171 Subject index 175 v THE PHYS I CS OF RUGBY vi INTRODUCT I ON IN T RODU cti ON ‘Rugby is a good occasion for keeping thirty bullies far from the centre of the city.’ Oscar Wilde ‘I prefer rugby to soccer. I enjoy the violence in rugby, except when they start biting each other’s ears off.’ Elizabeth Taylor his book began three decades ago, on a cold Saturday morning in early September. That was when I pulled on for the first time the Tscarlet jersey of Icknield, a high school named for a fierce tribe of Britons, the Iceni, who under their warrior queen Boadicea inflicted several heavy defeats upon the Romans. Our opponents that morning were from the Cardinal Newman School, named not after a warrior but a mild-mannered man who may soon become a saint of the Roman Catholic Church. The Cardinal’s men were victorious that day, the final score was 10-6 and, to show my age, we were defeated by two converted tries to two unconverted tries. But I was hooked. Chances are you are reading this book because you, too, fell in love with rugby. It has that effect on people. It’s a game of many parts. While a good deal of brawn is needed, brains play a big role too, and the post-game social life is usually enjoyable, if not entirely wholesome or suitable for family viewing. Rugby has grown immensely in recent years. There are now women’s teams at the international level and a women’s rugby world cup; there are national teams for the hearing impaired, and the sport spreads ever wider. As I write, Brazil conquered Trinidad and Tobago in the early qualifying stages of the next Rugby World Cup. There’s even a movement to reintroduce rugby in the Olympic Games, where the current reigning champions are the United States who defeated the French 17-3, in Paris, in 1924. vii THE PHYS I CS OF RUGBY For those whose playing days are over, the big screen gives us Murderball, which documents the 2002 World Wheelchair Rugby Championship, won by Canada. (The current world champions are the United States, who beat the Kiwis 34-30 in Christchurch). The small screen, your PC, allows you to play virtual rugby through games such as EA Sports’s Rugby08, as well as head up your own team through one of the many online fantasy rugby options. And the medium screen, TV, now features high-definition picture and surround-sound audio which, combined with referees wired for sound, make watching rugby more pleasurable than ever before. These are exciting times to be a spectator, whether in the flesh or via television. And if the gogglebox is not your thing, there are countless books on rugby to be read — some of which are included in the suggested reading section. This book, though, is slightly different. The second passion of my life is as far removed from rugby as you can hope to get. Rugby sparks almost endless conversations about great games you’ve seen, or similar playing experiences that you can share. Physics, on the other hand, is a conversation stopper. To mention that you study physics generates the response ‘I was never any good at that in school’ and the person will look into the far distance, silently, before drifting away to find someone else to talk to. The difficulty with physics is that, for so many people, it isn’t. I mean that large numbers of textbooks and teachers give students all the details of a problem and ask them to solve it. That’s not physics; it’s mathematics. In a physics laboratory practical, you aren’t usually asked to come up with an experiment to measure something; the equipment is all there and all you have to do is to take the data. To paraphrase Lord Rutherford of Nelson, that’s not physics; it’s stamp collecting. In school or college, there’s an odds on chance that you will have to analyse a rough block on an inclined plane. Who cares? But wait one moment. When two packs struggle for supremacy in the scrum, what happens if the pitch is not level? The weight force of both packs is aimed right at the centre of planet Earth. This means that some small part of the weight force acts directly downhill. Physics tells you, surprise surprise, that it’s going to be easier to push downhill than uphill. More important, it shows how you can model viii INTRODUCT I ON something as complex as two groups of humans shunting and grunting as a simple block of wood on an inclined plane. Suddenly the science has a real application and the student has done something that lies at the very core of physics: take a subject from the real world and approximate it by a simple, easily solvable system. The pupil has constructed a physical model to be tested and that, in my opinion, is what physics is all about. In the pages that follow, I try to paint a picture of rugby using the colours of physics. Throughout, I hope to show how rugby can provide great practice in creating real-world physical models, and how to use dimensional analysis and order of magnitude estimates to check them. Conversely, physics can also show you how to play better rugby. Newton, and in a sense Einstein, can help you improve your game; I’ve added pointers to improve your rugby wherever I can. The language of physics is mathematics. As you journey through the book from scrums, to backs who run, to backs who tackle, to those who kick, and to game day itself, there will be a few equations along the path. Only the simplest equations are contained in the main text. If you are studying for GCSE or A-level physics – or did so many years ago – you should be able to follow the text readily. There is a second layer. Gathered in the book are notes that go to a higher mathematical level. If you delight in calculus, you will find a treatment of the physics that suits your needs in those notes sections. At the end of the book, I’ve collected various suggestions for further reading and I’ve included a glossary of physics terms in case help is needed. There’s also an index of player names, so you can see if your favourite player has been included. My love for physics took me from an undergraduate at Queen Mary College, part of the University of London, to Magdalen College at Oxford. One Wednesday in November, I was riding my bike down the Iffley Road. I had just passed the track where Sir Roger Bannister ran the first four-minute mile when I had a premonition that I’d break something during the game that afternoon. As I rode along, I wasn’t particularly bothered. I’d played rugby for about 11 years and had only one black eye and a pulled hamstring to show for it. An arm or a leg wouldn’t be too much of a problem, I remember thinking. Within the hour I was in the back of an ambulance being moved, ix THE PHYS I CS OF RUGBY slowly and carefully, to the John Radcliffe hospital, for my neck was broken. The jersey I wore had to be cut off me (I still have it) and for close to nine months I was in clamped into various devices that resembled the medieval torture machines used in the Tower of London. Those nine months, it turns out, were among the most productive of my life – at least in terms of physics. With nothing to do but think, I could concentrate on my research topic, the physics of flowing fluids. When I was finally able to return to Oxford, I completed my doctoral thesis swiftly, thanks to a career-ending rugby injury from which, thankfully, I completely recovered.