The Physics of Hockey

199 Pages·2002·19.11 MB·English

by  Alain Haché

The Physics of Hockey
ALAIN HACHE
The Johns Hopkins University Press
Baltimore and London
© 2002 The Johns Hopkins University Press
All rights reserved. Published 2002
Printed in the United States of America on acid-free paper
246897531
The Johns Hopkins University Press
2715 North Charles Street
Baltimore, Maryland 21218-4363
www.press.jhu.edu
Library of Congress Cataloging-in-Publication Data
Hache, Alain, 1970-
The physics of hockey / Alain Hache.
p. cm.
Includes bibliographical references and index.
ISBN 0-8018-7071-2
1. Physics. 2. Hockey. 3. Force and energy. I. Title.
QC28 .H23 2002
530-dc21
2001008643
A catalog record for this book is available from the British Library.
To all my teammates through the years
and to the championship J9 96-97
U of T Physics hockey team

Contents
Introduction
IX
I
Chapter 1 ON ICE 1
I
Chapter 2 SKATING 33
I
Chapter 3 SHOOTING 64
I
Chapter 4 COLLISIONS AND PROTECTIVE GEAR 101
51
Chapter KEEPING THE NET 126
I
Chapter 6 THE GAME 144
Appendixes: On Heating Ice, Winning Streaks,
and Other Details 159
Glossary 173
Further Reading 17 7
Index 179
vii

Introduction
T
his book combines two very different elements-a science
and a sport-each ofw hich has its own attraction. The beauty
of physics is its ability to reduce very complex phenomena to
a few simple rules and equations. With these we can make predictions
and understand how nature generally works, even though in reality
there is great complexity. Because high school physics typically covers
a small range of subjects, many people have a limited idea of what
physics is used for. Some will tell you that physics is about finding
out how long it takes for a falling stone to reach the ground or
calculating the current through a light bulb. Although it can certainly
be used to do that, physics is applicable to a much wider array of
complex problems. To give an example, a team of scientists recently
used physical models to predict the behavior of large crowds in a
state of panic, like that which occurs when a fire breaks out in a
building. 1 It is well known that the tremendous pressures caused
by fans pushing against one another in an overcrowded stadium can
have tragic results, such as in 1989 when 95 soccer fans were crushed
in Hillsborough Stadium in Sheffield, England. Scientists made an
important discovery with their physical model of crowd behavior:
they found that strategically located columns near the exits could
reduce the pressure and increase the flow of people through the doors.
In other words, adding apparent obstructions could actually save
lives. This counterintuitive finding was not derived from experience
or trial and error (no one would dare set fires just to study crowd
behavior), but rather it was the result of harmless simulations on a
computer using models that obey simple physical laws. This is just
1. Popular Science, January 2001, p. 29.
ix
x Introduction
one remarkable example of how physics is used to deal with seemingly
unsolvable problems. After all, what is more complex and chaotic
than a panic-stricken crowd? Likewise, much insight can be gained
on the game of hockey using physical modeling.
The beauty of hockey seems quite different from what physics
offers. Using a few simple game rules, talented athletes can turn the
sport of hockey into an awesome spectacle full of unpredictable twists
and turns. It is this unpredictability that makes the game so much
fun to watch. From that viewpoint, physics and hockey appear to
be at opposite ends of the spectrum, but, put together, they render
each other service. Exploring that relationship is the main objective
of this book.
Applying physics to hockey helps us understand how aspects of
the sport work and lets us make use of that knowledge to improve
our game. On the flip side, talking about hockey in a physics con
text may promote interest in science for the public at large and, by
the same token, help create a better scientific culture (which many
will agree is somewhat lacking in our society). I know this from
experience, as students in my freshman mechanics class usually be
come interested when real-life examples are used, especially exam
ples from hockey. Applications such as these make abstract theories
come alive.
Physics has a long history of being successfully applied to sports.
Over the last 30 years there has been an explosion of research in
biomechanics and related fields. The knowledge has served, among
other things, to develop better designs for equipment and help reduce
sports injuries. The science and medicine of sports is now a well
established discipline with a strong academic presence in universities
around the world. Already, physics books have been published on
baseball, golf, skiing, running, sprinting, skating, and a whole slew of
other activities. I hope that this book will help fill a void by discussing
the physics of hockey.
Hockey may be fun to watch and study, but it's even more fun to
play. During my humble amateur career, I've had a chance to play
in many places and enjoy the company of people from all walks of
life. One great thing about the game is that it makes us leave our
cozy homes in the middle of the winter to meet and play with other
people. I must also say I've had a lot of fun writing this book. As
Introduction xi
a physicist and a hockey player, I sometimes can't help but think
about the game in a scientific way. Fortunately, hockey involves many
facets of physics, perhaps more than any other sport. Because it is
played on ice, we need to take into account elements of thermo
dynamics and molecular physics. Skating makes use of a great deal
of mechanics, as does shooting. Puck trajectories are influenced by
air drag and ice friction, which involve fluid dynamics. And because
hockey is a contact sport, the physics of collisions is also part of
the game.
In a way, my position as a goalie has given me a privileged view
of the game. Half the time, when the action is away from my zone,
I have the leisure to observe the game up close. This book greatly
benefited from countless hours of observation done over the years.
But of course, you don't need to be a goaltender or a scientist to enjoy
a good game of hockey!
This book could easily have been turned into a boring scientific
monograph. Instead, it is peppered with stories, real-life examples,
and anecdotes, and should be accessible to a wide range of readers,
including those with limited or no scientific background. I assumed
the average reader would have nothing more than a bit of high school
physics. However I did not want to leave out the scientifically inclined
readers, so there is also enough mathematics to satisfy their appetite.
Appendixes discuss the details of some important results covered in
this book.
To many people, including myself, equations sometimes can be a
turnoff. Though they are not the central part of this book, they are
included to help the reader apply the knowledge gleaned to other
situations. For example, someone may want to use the equation de
scribing puck motion to estimate how much it has slowed down by
the time it reaches the net after being shot from the red line. The
shape of the equation is often as instructive as the equation itself:
it tells us what parameters are important. In most cases, however, a
reader can skim the formulas and go through the discussion without
missing the main point.
An important point about physical units: because we are accus
tomed to speaking in terms of feet, miles per hour, and pounds, I
often use this language for discussions in the book. Unfortunately,
these units can create confusion if used in physics. So, unless stated