Physics for animators

338 Pages·2016·0.39 MB·English

by  Bousquet

Physics for Animators
Achieving believable motion in animation requires an understanding of
physics that most of us missed out on in art school. Although animators
often break the laws of physics for comedic or dramatic eff ect, you need to
know which laws you’re breaking in order to make it work. And while large
studios might be able to spend a lot of time and money testing diff erent
approaches or hiring a physics consultant, smaller studios and independent
animators have no such luxury. This book takes the mystery out of physics
tasks like character motion, light and shadow placement, explosions, ocean
movement, and outer space scenes, making it easy to apply realistic physics
to your work.
• Physics concepts are explained in animator’s terms, relating concepts
specifi cally to animation movement and appearance.
• Complex mathematical concepts are broken down into clear steps you
can follow to solve animation problems quickly and eff ectively.
• Bonus companion website at www.physicsforanimators.com off ers
additional resources, including examples in movies and games, links to
resources, and tips on using physics in your work.
Uniting theory and practice, author Michele Bousquet teaches animators
how to swiftly and effi ciently create scientifi cally accurate scenes and fi x
problem spots, and how and when to break the laws of physics. Ideal for
everything from classical 2D animation to advanced CG special eff ects, this
book provides animators with solutions that are simple, quick, and powerful.
Michele Bousquet is a longtime animator and instructor, and the author of
more than 20 books on computer animation. Her freelance animation work
has served clients like Autodesk and the Australian Broadcasting Corporation,
and she has taught university-level animation classes at countless locations,
including several art institutes. After years of answering questions about
physics from animation students, Michele took on the task of formulating the
answers into this book. Michele holds a Bachelor’s degree in Mathematics
and Computer Science from McGill University.
This page intentionally left blank
Physics for Animators
Michele Bousquet
with Alejandro Garcia
Boca Raton London New York
CRC Press is an imprint of the
Taylor & Francis Group, an informa business
A FOCAL PRESS BOOK
CRC Press
Taylor & Francis Group
6000 Broken Sound Parkway NW, Suite 300
Boca Raton, FL 33487-2742
© 2016 Taylor & Francis
CRC Press is an imprint of the Taylor & Francis Group, an informa business
This book contains information obtained from authentic and highly regarded sources.
Reasonable eff orts have been made to publish reliable data and information, but the
author and publisher cannot assume responsibility for the validity of all materials or
the consequences of their use. The authors and publishers have attempted to trace
the copyright holders of all material reproduced in this publication and apologize
to copyright holders if permission to publish in this form has not been obtained. If
any copyright material has not been acknowledged please write and let us know
so we may rectify in any future reprint.
Except as permitted under U.S. Copyright Law, no part of this book may be reprinted,
reproduced, transmitted, or utilized in any form by any electronic, mechanical,
or other means, now known or hereafter invented, including photocopying,
microfi lming, and recording, or in any information storage or retrieval system, without
written permission from the publishers.
For permission to photocopy or use material electronically from this work, please
access www.copyright.com (http://www.copyright.com/) or contact the Copyright
Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400.
CCC is a not-for-profi t organization that provides licenses and registration for a variety
of users. For organizations that have been granted a photocopy license by the CCC, a
separate system of payment has been arranged.
Trademark Notice: Product or corporate names may be trademarks or registered
trademarks, and are used only for identifi cation and explanation without intent to
infringe.
Library of Congress Cataloging-in-Publication Data
A catalog record for this book has been requested.
ISBN: 978-0-415-84298-3 (hbk)
ISBN: 978-0-415-84297-6 (pbk)
ISBN: 978-0-203-75825-0 (ebk)
Typeset in Myriad
by Apex CoVantage, LLC
Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC
Press Web site at http://www.crcpress.com
Contents
Acknowledgements xv
Foreword xvii
Introduction 1
SECTION 1
CLASSICAL PHYSICS 5
1 Matter and Masses 7
Matter 7
Composition of Matter 9
Atoms and Binding 11
Nuclear Fusion 13
Masses 14
Mass vs. Weight 14
Center of Mass 15
2 Motion and Timing 17
Motion Lines and Paths 17
Linear Motion 18
Circular Motion 19
Types of Circular Motion 19
Rotational Motion 20
Rotation and Distance 20
Calculating the Number of Times a Wheel Turns 21
Spinning, Tumbling, and Wobbling 21
Centripetal Motion 24
When Centripetal Force Stops 26
Circular Speed 26
Centrifugal Force 28
Centripetal Force and Vehicles 30
Pendulum Motion 32
Wave Motion 34
vi CONTENTS
What Waves Do 34
Visibility of Waves 34
Types of Waves 34
Transverse Waves 35
Longitudinal Waves 36
Wave Properties 37
Wave Relations 40
Wave Phase 40
Wave Addition and Cancellation 41
Standing Waves 42
Common Sound Eff ects 43
Resonance 43
Doppler Eff ect 44
Sonic Boom 45
Timing 46
Timing Tools 46
Uniform Motion Timing 46
Slow In and Slow Out 48
Acceleration Timing 48
Constant Forces 49
Forces Exerted by Characters 49
Constant Force and Acceleration 50
The Odd Rule 50
Odd Rule Multipliers 51
Odd Rule Scenarios 52
Motion Graphs 55
Constant Speed 55
Acceleration 55
Acceleration of Gravity 56
Swinging 56
3 Forces 57
Components of Force 60
Familiar and Unfamiliar Forces 60
Familiar, Non-Random Forces 61
Unfamiliar Forces 61
Variable Forces 62
Gravity 62
Gravitational Acceleration 62
Common Misconceptions about Gravity 63
Timing for Gravity 64
Calculating Total Time and Distance 64
Physics-Based Calculations 64
Visual Calculation Methods 65
The Odd Rule 65
Fourth Down at Half Time 66
CONTENTS vii
Falling à la Chai 67
Moving and Falling 67
Ascending Against Gravity 68
Projectile Velocity 68
Center of Gravity 70
Line of Gravity 71
Tipping and Center of Gravity 71
Lowering and Raising the CG 73
Friction 74
Static and Kinetic Friction 74
Friction on Flat Surfaces 76
Frictionless Surfaces 76
Coeffi cient of Friction 76
Eff ects of Friction 77
Pressure and Gases 78
Pressure Increase from Heat 79
Heated Gas in a Container 80
Heated Air in Atmosphere 80
Chemical Reaction 82
Force from Pressure Decrease 84
Atmospheric Pressure 84
Air Resistance 85
Aerodynamic Lift 86
Pressure Diff erences in Action 86
Torque 87
Torque Basics 88
Torque Terminology 88
Maximizing Torque 88
Visualizing Torque 89
Calculating Torque 89
Lever Systems 90
Effi ciency vs. Speed 91
Neutral Effi ciency 93
Lever System Classes 93
First Class Systems 93
Second Class Levers 93
Third Class Levers 94
Balancing Torque in a Lever System 95
Increasing Leverage 95
Torque in Animation 96
Rotational Inertia 96
Action/Reaction 98
Action/Reaction and Balanced Forces 98
Action/Reaction with Two Mobile Objects 98
Action/Reaction and Weight 99
Action/Reaction and Fixed Objects 100
viii CONTENTS
Electricity and Magnetism 101
Electricity 101
Electrical Charge 102
Static Electricity 102
Flowing Electricity 103
Electric Shock 106
Sparks and Lightning 107
Magnetism 107
Magnetic Fields 107
Visualizing Electricity and Magnetism 111
Electric Shock 111
Electric Current 111
Magnetism 112
EMPs 113
4 Light and Color 115
Light Basics 116
Light as Rays 116
Light and Refl ection 117
Seeing in a Mirror 118
Bouncing Light Rays 119
Attenuation 121
Physically Based Lights 122
Shadows 123
Cast Shadows 124
Umbra and Penumbra 125
Sharp and Fuzzy Shadows 127
Shadow Angle 128
Light Source Shapes 130
Shadow Intensity 131
Form and Occlusion Shadows 132
Refl ection 134
Specular Refl ection 135
Diff use Refl ection 136
Diff use Refl ection and Light Intensity 137
Detecting Shape and Color 139
Diff use vs. Specular Refl ections 139
Diff use Interrefl ection 141
Partial Refl ections 142
Refraction 145
Caustics 148
Gamma Correction 151
Linear vs. Curved Light Intensity 152
Gamma Correction for Real-World Perception 153
Gamma Correction and Cameras 154
Gamma Correction on Digital Files 156
CONTENTS ix
Gamma Calculations 156
Monitor Gamma Adjustment 157
RGB Gamma Curves 158
Linear Workfl ow 158
SECTION 2
CHARACTER DESIGN AND ANIMATION 161
5 Character Design 163
Size and Scale 163
Proportion and Scale 165
Weight and Strength 167
Physical Characteristics and Size 169
Posture 169
Deformability 170
Wing Size and Shape 170
Climate 171
Longevity 172
Sound 173
Babyness 173
Joints 175
Types of Joints 176
Animal Joints 178
Joints as Levers 179
Elbow 179
Foot 180
Neck 180
Muscles for Joints 180
Weight Distribution 181
Character Center of Gravity 182
Balance 183
Improving Balance 185
6 Character Animation 189
Jumping 189
Parts of a Jump 190
Calculating Jump Actions 192
Calculating Jump Timing 192
Jump Magnifi cation 193
Push Time 195
Push Key Spacing 196
Motion Arc and Jump Timing 197
Landing 198
Stop Time 198
Very High Jumps 199