How To Read online

  RIVERHEAD BOOKS

  An imprint of Penguin Random House LLC

  Copyright © 2019 by xkcd inc.

  Penguin supports copyright. Copyright fuels creativity, encourages diverse voices, promotes free speech, and creates a vibrant culture. Thank you for buying an authorized edition of this book and for complying with copyright laws by not reproducing, scanning, or distributing any part of it in any form without permission. You are supporting writers and allowing Penguin to continue to publish books for every reader.

  ISBN 9780525537090 (hardcover)

  ISBN 9780525537106 (ebook)

  ISBN 9780593086377 (international)

  While the author has made every effort to provide accurate internet addresses at the time of publication, neither the publisher nor the author assumes any responsibility for errors or for changes that occur after publication. Further, the publisher does not have any control over and does not assume any responsibility for author or third-party websites or their content.

  Version_1

  Contents

  Title Page

  Copyright

  Disclaimer

  Introduction

  1. How to Jump Really High

  2. How to Throw a Pool Party

  3. How to Dig a Hole

  4. How to Play the Piano

  → How to Listen to Music

  5. How to Make an Emergency Landing

  6. How to Cross a River

  7. How to Move

  8. How to Keep Your House from Moving

  → How to Chase a Tornado

  9. How to Build a Lava Moat

  10. How to Throw Things

  11. How to Play Football

  12. How to Predict the Weather

  → How to Go Places

  13. How to Play Tag

  14. How to Ski

  15. How to Mail a Package

  16. How to Power Your House (on Earth)

  17. How to Power Your House (on Mars)

  18. How to Make Friends

  → How to Blow out Birthday Candles

  → How to Walk a Dog

  19. How to Send a File

  20. How to Charge Your Phone

  21. How to Take a Selfie

  22. How to Catch a Drone

  23. How to Tell If You’re a Nineties Kid

  24. How to Win an Election

  25. How to Decorate a Tree

  → How to Build a Highway

  26. How to Get Somewhere Fast

  27. How to Be On Time

  28. How to Dispose of This Book

  Acknowledgements

  References

  Index

  → How to Change a Light Bulb

  About the Author

  Disclaimer

  Do not try any of this at home. The author of this book is an internet cartoonist, not a health or safety expert. He likes it when things catch fire or explode, which means he does not have your best interests in mind. The publisher and the author disclaim responsibility for any adverse effects resulting, directly or indirectly, from information contained in this book.

  Hello!

  This is a book of bad ideas.

  At least, most of them are bad ideas. It’s possible some good ones slipped through the cracks. If so, I apologize.

  Some ideas that sound ridiculous turn out to be revolutionary. Smearing mold on an infected cut sounds like a terrible idea, but the discovery of penicillin showed that it could be a miracle cure. On the other hand, the world is full of disgusting stuff that you could smear on a wound, and most of them won’t make it better. Not all ridiculous ideas are good. So how do we tell the good ideas from the bad?

  We can try them and see what happens. But sometimes, we can use math, research, and things we already know to work out what will happen if we do.

  When NASA was planning to send its car-size Curiosity rover to Mars, they had to figure out how to land it gently on the surface. Previous rovers had landed using parachutes and air bags, so NASA engineers considered this approach with Curiosity, but the rover was too large and heavy for parachutes to slow it down enough in Mars’s thin atmosphere. They also thought about mounting rockets on the rover to let it hover and touch down gently, but the exhaust would create dust clouds that would obscure the surface and make it hard to land safely.

  Eventually, they came up with the idea of a “sky crane”—a vehicle that would hover high above the surface using rockets while lowering Curiosity to the ground on a long tether. This sounded like a ridiculous idea, but every other idea they could come up with was worse. The more they looked at the sky crane idea, the more plausible it seemed. So they tried it, and it worked.

  We all start out life not knowing how to do things. If we’re lucky, when we need to do something, we can find someone to show us how. But sometimes, we have to come up with a way to do it ourselves. This means thinking of ideas and then trying to decide whether they’re good or not.

  This book explores unusual approaches to common tasks, and looks at what would happen to you if you tried them. Figuring out why they would or wouldn’t work can be fun and informative and sometimes lead you to surprising places. Maybe an idea is bad, but figuring out exactly why it’s a bad idea can teach you a lot—and might help you think of a better approach.

  And even if you already know the right way to do all these things, it can be helpful to try to look at the world through the eyes of someone who doesn’t. After all, for anything that “everyone knows” by the time they reach adulthood, every day over 10,000 people in the United States alone are learning it for the first time.

  That’s why I don’t like making fun of people for admitting they don’t know something or never learned how to do something. Because if you do that, all it does is teach them not to tell you when they’re learning something . . . and you miss out on the fun.

  This book may not teach you how to throw a ball, how to ski, or how to move. But I hope you learn something from it. If you do, you’re one of today’s lucky 10,000.

  CHAPTER 1

  How to Jump Really High

  People can’t jump very high.

  Basketball players make some impressive leaps to reach hoops placed high in the air, but most of their reach comes from their height. An average professional basketball player can only jump a little more than 2 feet straight up. Non-athletes are more likely limited to jumping a foot or so. If you want to jump higher than that, you’ll need some help.

  Using a running start can help. This is what athletes competing in the high jump do, and the world record height is 8 feet. However, that’s measured from the ground. Since high jumpers tend to be tall, their center of mass starts off several feet off the ground, and because of how they fold their bodies to pass over the bar, their center of mass may actually pass under it. An 8-foot high jump doesn’t involve launching the center of their body anything like the full 8 feet.

  If you want to beat a high jumper, you have two options:

  Dedicate your life to athletic training, from an early age, until you become the world’s best high jumper.

  Cheat.

  The first option is no doubt an admirable one, but if that’s your choice, then you’re reading the wrong book. Let’s talk about option two.

  There are a lot of ways you could cheat at high jump. You could use a ladder to get over the bar, but that’s hardly jumping. You could try wearing those spring-loaded stilts* popular with extreme sports enthusiasts, which—if you’re athletic enough—might be enough to give you the edge over an unassisted high jumper. But for sheer vertical height, athletes ha
ve already come up with a better technique: pole vaulting.

  In pole vaulting, athletes start running, stick a flexible pole into the ground in front of them, and launch themselves into the air. Pole vaulters can fling themselves several times higher than the best unassisted high jumpers.

  The physics of pole vaulting are interesting, and don’t revolve around the pole nearly as much as you might think. The key to vaulting isn’t the springiness of the pole, it’s the athlete’s running speed. The pole is just an efficient way to redirect that speed upward. In theory, the vaulter could use some other method to change direction from forward to up. Instead of sticking a pole in the ground, they could jump onto a skateboard, go up a smooth curved ramp, and reach just about exactly the same height as the vaulter.

  We can estimate a pole vaulter’s maximum height using simple physics. A champion sprinter can run 100 meters in 10 seconds. If an object is launched upward at that speed under Earth’s gravity, a little math can tell us how high it should go:

  Since the pole vaulter is running before they jump, their center of gravity starts off above the ground already, which adds to the final height it reaches. A normal adult’s center of gravity is somewhere in their abdomen, usually at a height of about 55 percent of their actual height. Renaud Lavillenie, the world record holder in the men’s pole vault, is 1.77 meters tall, so his center of gravity adds another 0.97 meters or so, giving a final predicted height of 6.08 meters.

  How does our prediction compare to reality? Well, the actual world record height is 6.16 meters. That’s pretty close for a quick approximation!*

  Of course, if you show up at a high jump championship with a vaulting pole, you’ll be immediately disqualified.* But while the judges might object, they probably won’t stop you, especially if you wave the pole around threateningly as you approach.

  Your record won’t go on the books, but that’s ok—you’ll know in your heart how high you jumped.

  But if you’re willing to cheat more blatantly, you can go higher than 6 meters. A lot higher. You just need to find the right spot to launch from.

  Runners take advantage of aerodynamics. They wear sleek, tight-fitting outfits to cut down on air resistance, which helps them to gain greater speeds and thus soar higher.* Why not take it a step further?

  Of course, actually pushing yourself forward with a propeller or a rocket doesn’t count. There’s no way you can call that a “jump” with a straight face.* That’s not a jump, that’s a flight. But there’s nothing wrong with just . . . gliding a little.

  The path of every falling object is affected by how the air moves around it. Ski jumpers adjust their shape to gain a huge aerodynamic boost to their jumps. In an area with the right winds, you can do the same thing.

  When sprinters run with the wind at their backs, they can reach higher speeds. Similarly, if you jump in an area where the wind is blowing upward, you can reach greater heights.

  It takes strong wind to push you upward—wind blowing faster than your terminal velocity. Your terminal velocity is the maximum speed you’ll reach while falling through air, when the force of the air rushing past balances out the downward acceleration of gravity. This is the same as the minimum upward wind speed needed to lift you off the ground. Since all motion is relative, it doesn’t really matter whether you’re falling downward through the air or the air is blowing upward past you.*

  People are a lot denser than air, so our terminal velocity is pretty high. A falling person’s terminal velocity is around 130 miles per hour (mph). In order to get much of a boost from wind, you’ll need the upward wind speed to be at least in the same range as your terminal velocity. If the wind is a lot slower, then it won’t affect your jump height very much.

  Birds use columns of warm, rising air—called thermals—like elevators. The birds soar in circles without flapping, letting the rising air carry them upward. These thermal updrafts are relatively weak; to lift your larger human body, you’ll need to find a stronger source of rising air.

  Some of the strongest updrafts near the ground happen near mountain ridges. When wind encounters a mountain or ridge, the airflow can be diverted upward. In some areas, these winds can be quite fast.

  Unfortunately, even at the best spots, the vertical winds generally aren’t even close to a human’s terminal velocity. At best, you’d only gain a little bit of height from the wind’s assist.*

  Instead of trying to increase the wind speed, you can try reducing your terminal velocity with aerodynamic clothing. A good wingsuit—clothing with sheets of material between the arms and legs—can reduce a person’s sink rate from 130 mph to as little as 30 mph. That’s still not enough to actually ride winds upward, but it would add some height to your jump. On the other hand, you’d have to do your running approach in a full wingsuit, which would probably cancel out the benefit from the wind.

  To add substantial height to your jump, you need to go beyond wingsuits, into the world of parachutes and paragliders. These large contraptions reduce a person’s falling speed enough so that surface winds can easily get strong enough to lift them. Skilled paragliders can launch from the ground and ride ridge winds and thermals to thousands of feet.

  But if you want a real high jump record, you can do even better.

  In most areas where air flows over mountains, the “mountain waves” extend up only into the lower atmosphere, which limits the height that gliders can reach. But in some places, when conditions are just right, these disturbances may interact with the polar vortex and polar night jet,* creating waves that reach into the stratosphere.

  In 2006, glider pilots Steve Fossett and Einar Enevoldson rode stratospheric mountain waves to over 50,000 feet above sea level. That’s almost twice as high as Mt. Everest, and higher than the highest commercial airline flights. That flight set a new glider altitude record. Fossett and Enevoldson say they could have ridden the stratospheric waves even higher—they only turned back because the low air pressure caused their pressure suits to inflate so much that they couldn’t operate the controls.

  If you want to jump high, you just need to construct an outfit shaped like a sailplane—you can make one out of fiberglass resin and carbon fiber—and head to the mountains of Argentina.

  If you find the right spot, and if conditions are just right, you can seal yourself into your sailplane suit,* jump into the air, catch the ridge lift, and ride the wind into the stratosphere. It’s possible that a glider pilot riding these waves might be able to cruise at higher altitudes than any other wing-borne aircraft. That’s not bad for a single jump!*

  If you’re really lucky, maybe you can find a spot that’s upwind from where the Olympics are being held. That way, when you jump off the edge, the winds in the stratosphere will carry you over the venue . . .

  . . . letting you set the greatest high jump record in the history of the sport.

  They probably won’t give you a medal, but that’s fine. You’ll know you’re the real champion.

  CHAPTER 2

  How to Throw a Pool Party

  You’ve decided to throw a pool party. You’ve got everything—snacks, drinks, floating inflatable toys, towels, and those rings you throw into the pool and then have to dive in to retrieve. But the night before the party, you can’t shake the feeling that you’re missing something. Looking around your yard, you realize what it is.

  You don’t have a pool.

  Don’t panic. You can solve this problem. You just need a bunch of water and a container to put it in. Let’s figure out the container first.

  There are two main types of pools: in-ground and above-ground.

  IN-GROUND POOL

  An in-ground pool is, when it comes down to it, a fancy hole. This type of pool can take more work to install, but is also less likely to collapse in the middle of your party.

  If you’d like to build an in-ground pool, first consult chapter 3: How to
Dig a Hole. Use those instructions to dig a hole roughly 20 feet by 30 feet by 5 feet. Once you’ve created a hole of the appropriate size, you may want to line the walls with some kind of coating to keep the water from turning to mud or draining out before the party is over. If you have some giant plastic sheets or tarps lying around, you can use those, or you can try a spray-on rubber coating—there are ones designed for lining the beds of koi ponds. Just tell the salespeople you have some really large koi.

  ALTERNATIVE: ABOVE-GROUND POOL

  If you decide an in-ground pool isn’t the option for you, you can instead try an above-ground pool. The design of this type of pool is relatively simple:

  Unfortunately, water is heavy—ask anyone who’s ever filled a fish tank on the floor and then tried to lift it up onto a table. Gravity pulls the water downward, but the ground pushes back equally hard. The water pressure is redirected outward, toward the walls of the pool, which are stretched in all directions. This tension, called hoop stress, is strongest at the base of the wall where the water pressure is the highest. If the hoop stress exceeds the tensile strength of the wall, the wall will burst.*

  Let’s pick a possible material—say, aluminum foil. How deep can the water in an aluminum-foil-walled pool get before the sides burst? We can figure out the answer to this question, and lots of other pool design questions, using the formula for hoop stress:

  Let’s plug in the numbers for aluminum foil. Aluminum has a tensile strength of around 300 megapascals (MPa), and sheets of foil are roughly 0.02 mm thick. Let’s assume our pool is 30 feet in diameter, so there’s plenty of room for games. We can plug those values into the hoop stress equation and rearrange things to figure out how deep the water in our shiny, crinkly pool can get before the hoop stress equals the tensile strength of the aluminum and the walls give out: