The Ultimate Guide to Almost Everything

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The seven colors of the visible spectrum of light are always present in a rainbow: red, orange, yellow, green, blue, indigo and violet.

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diydou table of contents ever CHAPTER 1 wonder? SPACE Is there really the Discover what’s out there among possibility of life on another planet? 6 the planets and stars, plus what we How do our bodies can learn from our explorations. work to help us avoid getting sick? 26 CHAPTER 2 What’s the best way to invent something THE HUMAN new? Who is the BODY fastest human? Why does science Take a closer look at the many ways even matter? Asking your different systems work together. questions like these helps us learn and 42 CHAPTER 3 explore lots of new 60 things. On these 80 INVENTIONS pages, you’ll find the answers to some Learn about some of the of your biggest coolest machines and devices that questions—and quite people have created to make life a few more that you may never have even safer and easier for us all. thought of! Being curious is how we get CHAPTER 4 smarter and make the world a better SPORTS place. You never know: The questions Explore the wild, wonderful you come up with and sometimes weird world of may lead to science’s athletics—a place where anything next big discovery. can (and often does) happen! So keep on reading CHAPTER 5 and enjoy the adventure ahead! SCIENCE 4 POPULAR SCIENCE KIDS Everything around you has been poked, prodded, questioned and, in many cases, improved by scientists. See why their discoveries matter.



CHAPTER 1 SPACE Every night and every day, people look to the sky and wonder. While we know a bit about space, there’s a lot more we don’t know. To satisfy our curiosity, we have built all sorts of machines and devices over the centuries. In 1609, Galileo was the first person to use a telescope to scientifically observe and record his observations of the nighttime sky. Since then, humans have found many ingenious ways to study space. In 2020, for example, NASA, the space agency of the United States, landed a probe on an asteroid. We even have remote-controlled rovers that scour the Martian landscape, searching for water, ice and, yes, life. We have explorers that zoom across our solar system constantly, telling us what our backyard looks like. What we have learned boggles the mind. What we don’t know inspires us. That’s the infinite wonder of space!

Jupiter is the most massive planet in our solar system and also the fastest. One day— a complete rotation on its axis—takes about 10 hours. The James Webb Space Telescope launched on Dec. 25, 2021. It can see through space dust and is designed to answer important questions about the universe, and to capture amazing images, like the one you see here.

SPACE Venus Earth why With its dense Earth is the only atmosphere, planet we know of is Earth Venus is the with liquid water called hottest planet in on its surface. our solar system. the third Distance From rock Distance From the Sun the Sun 93 million miles from the 67 million miles (150 million km) sun? (108 million km) Orbit, in Earth Orbit, in Earth Days 365 T here are eight primary planets Days 225 in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Mercury Saturn, Uranus and Neptune. One day on Planets all orbit a star, and the Mercury takes star in our cosmic community is 59 Earth days, the sun. It is the center of our solar due to its slow system and the largest thing in it— rotational speed. it contains 99.8% of the mass of the entire system! Distance From the Sun Each planet is a different 35 million miles distance from the sun. The (58 million km) four outer planets are known Orbit, in Earth as the gas giants. They all are Days 88 huge, have rings and are made of mostly gas. The four inner you don’t say! planets—those closest to the sun—are made of rock and Probes from Earth have taken metals. These planets all have a close look at all the planets in solid surfaces and are called our solar system, including the terrestrial. Mercury is closest to dwarf planets Pluto and Ceres. the sun, Venus is second closest and Earth is the third rocky 8 POPULAR SCIENCE KIDS

Jupiter Uranus Jupiter’s dark-red Unlike other spot is a storm planets, Uranus larger than all is tilted at a of Earth. 90-degree angle— it rotates on Distance From its side. the Sun 484 million miles Distance From (778 million km) the Sun Orbit, in Earth 1.78 billion miles Days 4,333 (2.87 billion km) Orbit, in Earth Days 30,687 Mars Saturn Neptune Also known as the Saturn has a Neptune is the red planet, Mars complex ring windiest planet in has a layer of system and our solar system. rusty dust made of dozens of moons. Clouds speed oxidized iron on its around it at up surface. It’s much Distance From to 1,200 miles per colder than Earth— the Sun hour (2,000 kph). the average temp 887 million miles is -80°F (-60°C). (1.43 billion km) Distance From Orbit, in Earth the Sun Distance From Days 10,759 2.8 billion miles the Sun (4.5 billion km) 142 million miles Orbit, in Earth (228 million km) Days 60,190 Orbit, in Earth Days 687 9

SPACE what star is closest to Earth? T he sun! A giant ball of superheated gases, the sun is at the center of our solar system. It is one of 100 billion stars in our galaxy, and because it is closest, its light is the one that shines most brightly on Earth. The sun’s light is the reason you, and most living things on our planet, exist. Fueled by fusing together hydrogen atoms, the part of the sun that we can see is about 10,000°F (5,500°C). Deep in its core, though, temperatures rise to a blistering 27 million°F (15 million°C).

5 SURPRISING FACTS ABOUT THE SUN 1/ The sun has enough fuel to last about 5 billion more years. 2/ Sunspots are dark, cool areas on the sun’s surface. 3/ The sun is nearly 93 million miles (150 million km) away from Earth. It takes about 10 minutes for its light to reach Earth. 4/ Solar flares are eruptions of energy caused by the sun’s magnetic field. 5/ The sun was formed some 4.5 billion years ago from a giant spinning cloud of gas and dust.

SPACE On Nov. 28, 1964, NASA launched what the Mariner 4 have we spacecraft—and on learned from July 14, 1965, it made the first flyby of exploring the red planet. As it Mars? did, it sent up-close photographs back N o planet in our solar system has captured our to Earth. Although imagination more than Mars. Sitting in the night NASA expected sky, the reddish orb is named for the Roman god of war Mariner 4 to last and is the most explored planet in our solar system. about eight months, it kept sending back Four space agencies have successfully sent dozens photos for three of missions to Mars since the 1960s, each gathering years. NASA sent whatever information it could find. Some were several other Mariner photographic flybys; others dispatched rovers that craft to Mars, as poked, prodded and tested Mars’ surface. well as to Venus and Mercury. Scientists study Mars for many reasons—most notably, to see if life exists, or did, and to understand our own planet’s evolution. Unlike other planets, Mars is neither too cold nor too hot, which could make it a good place for life to exist. Mars is also rich in carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur— elements scientists believe are essential for life. What we’ve learned so far has been astounding. Although dry now, Mars was once a huge water park. Most of the water on Mars now is ice, but evidence suggests that from time to time, liquid water still runs across its surface. The latest Mars rover is Perseverance, which arrived in 2021. It will take rock samples that a future mission will bring back to Earth. Perseverance landed in a crater that scientists believe may contain evidence of Martian bacteria—or, at least, fossils of ancient bacteria. 12 P O PU L AR SC I E N C E K I DS

Viking 1 and Viking 2 made By the 1990s, humans history in 1976, when they were eager to go four- became the first spacecraft wheeling on the red from Earth to land on a planet. planet. On July 4, 1997, It took the landers nearly a the Mars Pathfinder, year to reach their destination. which included a rover The landers and their orbiting named Sojourner, touched probes then went to work. down. Controlled by a The landers conducted an human on Earth, the six- experiment, which found that wheeled rover provided detailed pictures of the surface of Mars is rich the planet as it studied in iron that oxidizes rocks and soil. The data (rusts) when wet. Iron from Mars Pathfinder oxide gives Mars suggested that Mars had its reddish tint. been warm and wet at The orbiters also some (as yet unknown) mapped 97% of the point in the past. planet’s surface. In 2004, two six-wheeled robots, Spirit and Opportunity, landed on opposite ends of Mars to look for evidence of water. Each bounded across the surface, conducting experiments and sending thousands of crystal-clear photographs back to Earth. They were supposed to only last three months, but they kept roaring along. Spirit stopped talking to controllers in 2010; Opportunity did the same in 2018. The rovers had collected masses of information about the makeup of Martian rocks and soil.

SPACE who was the first human in space? Y uri Gagarin flew one mission, but what a mission it was! On April 12, 1961, the cosmonaut blasted off from the Soviet Union to become the first human in space. For 108 minutes, Gagarin orbited Earth, speeding along at 16,777 miles (27,000 km) per hour. He was only 27 years old. Gagarin’s flight touched off the space race between the Soviet Union and the United States. who was the first American in space? Less than a month after Gagarin’s flight, Alan Shepard (left) blasted off from Florida’s Cape Canaveral, becoming the first American in space. Strapped into a Mercury capsule called Freedom 7, Shepard did not orbit the planet. Instead, he flew 116 miles (187 km) straight up, then safely splashed down. In 1962, John Glenn became the first U.S. astronaut to orbit Earth. who was the first woman in space? Valentina Vladimirovna Tereshkova (right), a Soviet cosmonaut, orbited Earth 48 times in 1963. In 1982, Svetlana Savitskaya became the first woman to fly to a space station when she joined the crew of the Soviet Union’s Salyut 7 space station. She went into space again in 1984 and was the first woman to walk in space. The United States sent its first woman—Sally Ride—into space in 1983.

who were the 8 Mercury 13? RADICAL SPACE Long before Sally Ride blasted off, a group of FLIGHT RECORDS women known to history as the Mercury 13 tried desperately to go where no male—or female— 1/ Oldest Person in Space John Glenn had gone before. was 77 when he flew aboard the space shuttle Discovery in 1998. The Mercury 13 weren’t astronauts, but they came pretty close. Here’s the scoop: America’s 2/ Youngest Person in Space Gherman first astronauts were known as the Mercury 7, Titov was 25 when he orbited Earth in named for Project Mercury, the first American 1961. He was also the first person to space flights with humans aboard. The Mercury sleep in space. 7 were all men. Yet NASA also recruited 13 female pilots. It was a secret program 3/ Shortest Space Flight Alan Shepard’s developed by Dr. William Randolph Lovelace, May 5, 1961, flight lasted just over a medical doctor at NASA. He recruited the 15 minutes. women and put them through the same rigorous tests and training as the male astronauts. 4/ Most Consecutive Days in Space Valery Polyakov, a Russian cosmonaut, spent The women were officially called the First 438 days aboard the Mir space station, Lady Astronaut Trainees—FLAT, for short. They from January 1994 to March 1995. never did get a chance to fly into space, though, chiefly because they were women. At the time, 5/ Farthest Human Flight From Earth NASA stated that all its astronauts The ill-fated Apollo 13 crew had to fly needed to be military test pilots around the far side of the moon in April and engineers. 1970, after an explosion on the ship nearly killed them. At the farthest point, how many they were 248,655 miles (400,171 km) astronauts from home. have walked on the moon? 6/ Most Time Spent in Space Russian cosmonaut Gennady Padalka spent 878 The moon is a six-day round trip, and only days, over five flights. U.S. astronaut 12 human beings have walked on its surface. Peggy Whitson spent a total of 665 days, The first was Neil Armstrong, on July 20, over three missions to the International 1969. He was followed by Edwin “Buzz” Space Station. Aldrin. Both were part of the Apollo 11 crew. Eugene Cernan and Harrison Schmitt, 7/ Fastest Human Flight Apollo 10 aboard Apollo 17, were the last. reached a jaw-dropping top speed of 24,791 mph (39,897 kph). 8/ First Walk in Space Soviet cosmonaut Alexei Leonova went for a 12-minute walk on March 18, 1965. 15

SPACE where do comets come from? W hen our solar system formed, about 4.5 billion years ago, it left a lot of rocky junk around. Some of those rocks are comets—dirty snowballs made from a combination of frozen gases, dust and rock. Some comets are very large, with tails that can stretch to about 100 million miles (160 million km) long. Most can be found in a far-off place known as the Oort Cloud—way beyond Pluto, at the edge of our solar system. when can you see a comet? Compared to other things in the universe, comets are small. Yet every once in a while, we can spot one in the night sky. When a comet gets close to the sun, the ice on the comet’s surface starts to melt. The sun’s energy pushes all those dust particles and gases, including carbon dioxide, ammonia and more, away from the center of the comet. As a result, a bright tail appears. That’s because the sun’s radiation changes the gases released by the comet into a streak of ions (particles with an electric charge), which light up the night sky. what is a near-Earth object? Every now and then, an asteroid or other space object gets very close to Earth. Scientists call these wayward travelers near-Earth objects, or NEOs. In 2019, one NEO whooshed past Earth, traveling at 10,400 miles per hour (16,740 kph). That space rock, officially known as Asteroid2006 QQ23, came within 4.6 million miles (7.4 million km) of slamming into the planet—a near miss. It was more than 400 feet (122 m) taller than the Empire State Building. Had it head-butted Earth, the devastation could have been enormous. 16 P O PU L AR SC I E N C E K I DS

what is a meteor? what is an asteroid? When a fragment of an asteroid, or particles of Asteroids are small rocks a comet, springs loose that orbit the sun. In fact, and comes hurtling into between Jupiter and Mars Earth’s atmosphere, is the Asteroid Belt, where that’s a meteor. Meteors many asteroids orbit our often appear as a bright solar system. Others, streak of light. however, bounce around farther from the sun. They can be as small as a school bus or as large as Texas. when is a meteor called a meteorite? If a meteor survives its journey through the atmosphere and lands on Earth’s surface, it becomes a meteorite. Every now and then, a comet will spring loose from the Oort Cloud and start zipping around the sun. Some, like Halley’s Comet, do so on a regular schedule. Known as a short-period comet, Halley’s reappears on a regular 76-year schedule as it orbits the sun. The comet’s next appearance will be in 2061. 17

SPACE The idea was to build the ISS in stages. By the time how it was finished, it was the size of a football field. does the International how fast is its orbit? Space Station work? The ISS rockets around the planet at 5 miles U sually, a house doesn’t take 10 years (8 km) per second. If you to build. But when that house is the were able to go that International Space Station (ISS), you want to fast, you could travel make sure everything is perfect. After all, you from the Empire State can’t call a plumber if the toilet leaks in space! Building in New York City to the White House In the 1980s, the U.S., Russia, Japan, Canada in Washington, D.C., in and the European Space Agency decided to about 40 seconds. pool resources and build a large space station orbiting high above Earth. Although there were orbiting space stations—the Soviet Union had Mir, and the U.S. had Skylab—the ISS is the largest spacecraft ever. While Russia has said they won’t continue after 2024, there's still plenty of international cooperation up high. what kind of work goes on at the ISS? Crews have conducted hundreds of experiments in an environment with limited gravity (known as microgravity). They’ve looked for answers to combat illnesses like cancer; tested water purification systems, to help those on Earth who lack clean drinking water; examined how long-term exposure to microgravity changes the body; grown food; and studied hurricanes, wildfires and climate change.

Modules The first crew 10 made by arrived in Russia, November AMAZING the United 2002; by 2009, FACTS ABOUT States, the station Japan, was fully THE ISS Canada and operational. It’s Europe were powered by an 1/ It circles the Earth every launched acre of solar 90 minutes. into orbit. panels that convert energy 2/ It’s the brightest object Construction in space from the sun in our night sky—with the began in 1998. Modules into electricity. exception of the moon were added one by one, and Venus. connected by a node. 3/ Astronauts can dock eight spaceships at one time. 4/ More than 50 computers keep everything humming along as it should. 5/ It has a mass of 925,335 pounds (419,725 kg). 6/ About eight miles (13 km) of wire connects the ISS electrical system. 7/ There’s an app that will tell you where the ISS is located at any moment. 8/ It only takes about four hours to reach the ISS after blasting off. 9/ Each day, the ISS travels 478,000 miles (769,200 km), which is equal to a round trip from Earth to the moon. 10/ Oxygen is generated on board using an electrical current that splits water molecules into hydrogen and oxygen gas. 19

SPACE how many times a year how does a piece much of space junk space junk strike Earth? is floating in orbit Most of it burns up in the atmosphere as it falls. Sometimes, around though, the pieces are too large to Earth? totally burn up. Luckily, Earth is mostly water, so much of that debris lands in W e humans generate a lot of oceans or in regions where not a lot trash, even in space. All this of people live. Over the past 50 years, junk comes from more than 60 years an average of one piece of space of people launching things into debris has fallen to Earth each day. orbit. Some are pieces of machinery, while some of it comes from have satellites ever satellites and other human-made collided in space? objects that slam into one another. Yes! In 2009, a Russian satellite that was no longer in use slammed into a U.S. communications satellite 50 miles (80 km) above Siberia in eastern Russia. As best as officials could tell, this was the first time a space collision had taken down two satellites. what’s the largest craft to fall from space? On March 23, 2001, the Russian space station Mir fell to Earth. For 15 years, Mir was a workhorse of a laboratory, but by 2001, it had served its purpose. The Russians brought the space station, which was as large as six school buses, down in a controlled reentry. It crashed into the Pacific Ocean. 20 P O PUL AR SC I E N C E K I DS

Most orbital debris There are about 500,000 travels in low-Earth pieces of space junk orbit, some 1,250 orbiting Earth. Of that, more miles (2,012 km) above than 23,000 pieces are the surface. Many larger than 4 inches (10 cm) satellites, including across. Each piece travels at the International up to 17,500 miles per hour Space Station, (28,163 kph). orbit the planet at a higher altitude. Researchers are studying ways to what happened solve the problem when Skylab fell? of orbital debris. A RemoveDEBRIS Skylab was a U.S. space satellite is designed station, built out of to experiment with spare parts from the different ways of Apollo moon missions. capturing pieces of It was launched atop space junk in orbit. Saturn V on May 14, 1973. Astronauts traveled back has the ISS ever had and forth to it for a few to dodge space junk? years. Then, on July 11, 1979, it fell from its orbit. Yes! Like a boxer in a title match, the ISS has Most of it fell into the had to sometimes bob and weave to dodge Indian Ocean, but several a piece of space trash. On Earth, there is a pieces slammed into network that tracks potential collisions. If Western Australia. After an object is spotted within a few kilometers it came down to Earth, of the ISS, it will move itself out of harm’s the Australian town of way. This happens about once a year. Esperance fined NASA $400 for littering. NASA 21 never paid the fine, but in 2009 a radio disc jockey in California collected the money from his listeners and sent it to the town.

SPACE how fast is the universe what expanding? is dark matter? A universe that is expanding slowly would keep its galaxies close N early 27% of the universe’s together, making them appear mass is made up of something brighter. A universe that is expanding scientists know very little about— rapidly would mean there’s a greater dark matter. But scientists know it’s distance between galaxies, making out there by studying how its gravity them appear dimmer. It turns out, the affects stars and galaxies. Dark galaxies do look dimmer. Scientists matter is made of particles that don’t knew something was pushing all give off light or energy or reflect these objects and the universe apart. light, so what exactly it is remains a They called it dark energy. They mystery. Some think that dark matter deduced that dark energy is a natural contains bizarre particles left over force in space that is actually stronger from the formation of the universe. than gravity—the force that pulls everything together. Scientists think 68% of the universe is dark energy. What does all that mean? It means the universe is expanding rapidly. 22 POPUL AR SCIENCE KIDS

Scientists studying dark matter think it forms long streams, or “hairs,” around planets like Earth, as shown in this illustration. how do we know that dark matter exists? Yes, seeing is believing. But sometimes, scientists don’t work like that. They work like detectives, deducing the workings of the universe from the known facts. New instruments help too. NASA’s Chandra X-Ray Observatory revealed that a faraway galaxy has a ton of dark matter at its tightly compacted core. By studying this galaxy, scientists hope to answer more questions about dark matter. what is the difference between dark matter and dark energy? Think of dark matter as a type of cosmic glue that holds our universe together. Dark energy is the reason the universe is expanding. In 1998, the Hubble Space Telescope snapped a picture of a supernova. It showed that 15 billion years ago, the universe was slowly expanding. But the supernova was actually brighter than it should have been, if the universe was expanding at a constant rate. Astronomers realized that about 7.5 billion years ago, the universe had begun expanding faster and faster.

SPACE who was the first chimpanzee in space? On Jan. 31, 1961, three months before Alan Shepard became the first American in space, a chimpanzee named Ham (left) flew in a Mercury space capsule just above Earth’s atmosphere. Before Ham, NASA launched a rhesus monkey named Albert I in 1948, aboard a V-2 rocket. Yorick, another monkey, made the trip in 1951, along with 11 mice. They all made it home safely. Ten months after Ham, another American chimp, Enos, orbited Earth. Since those early flights, a whole barnyard—including mice, rats and even spiders—has flown into space. who spent the which spacecraft longest time on the has flown the moon’s surface? farthest? That honor goes to the crew of Apollo 17, In the 1970s, NASA scientists had the last human mission to the moon. an important question: What are Astronauts Harrison Schmitt and Eugene Jupiter, Saturn and all the other Cernan spent more than 22 hours outer planets in our solar system walking on the moon plus more than like? To find out, they built two space three days, total, riding, sleeping and probes, Voyager 1 and Voyager 2. eating there in December 1972. Both were launched in 1977. In 2012, Voyager 1 reached the boundary 24 POPUL AR SCIENCE KIDS of our solar system and entered interstellar space—the area between stars. No human-made spacecraft had traveled so far. Voyager 2 was close behind, flying a different route and at a different speed. In 40,000 years or so, Voyager 1—if it’s still chugging along—will come within n astronomical whisker (1.7 light- years) of a star called AC +79 3888, which is some 17.5 light-years from Earth. (A light-year is the distance light travels in a year.)

which spacecraft cost the most money to build? The winner is the International Space Station (ISS), which had a price tag of $100 billion. That’s not including the $3.4 billion a year it takes to keep the massive spaceship in tip-top condition. The ISS orbits Earth 16 times a day, which means that those aboard see 16 sunsets and 16 sunrises every day. what are the most powerful rockets? The Saturn V rocket, which carried humans to the moon in the 1960s and 1970s, was the most powerful rocket for a long time. It stood 363 feet (111 m) tall and weighed as much as 214 school buses. Its five engines produced 7.5 million pounds (3,402 metric tons) of thrust at liftoff—more than enough to wrench itself free from Earth’s gravitational grip. Engineers built the rocket in three stages, each with its own set of engines. When one stage exhausted its fuel supply, it separated and the next stage took over. But in 2022, NASA made plans to send a new rocket, the Space Launch System, to the moon. This powerful rocket has about 15% more thrust and will be able to carry a payload of 27 tons (24 metric tons).

CHAPTER 2 THE HUMAN BODY Our bodies are amazing machines. They’re made of trillions of tiny building blocks called cells. Your body makes it possible for you to walk, run, climb, jump, think, feel and perform incredible physical feats. Different systems in your body work together to help you survive and do all these things. Each has its own organs that perform important functions, from your brain, which controls everything you do, to your heart, which pumps your blood. Turn the pages to take a closer look at your awesome body—inside and out.

People produce about a quart (a liter) of saliva a day. That’s more than two full bathtubs a year. Yoga is a kind of exercise that helps keep your body strong, balanced and flexible.

THE HUMAN BODY Your cerebrum is divided into two which halves, called organ is the hemispheres. The boss of left half controls the muscles on the right everything? side of your body, while the right half C an you clap your hands? Solve a math controls the muscles problem? Remember your way to school? Ride on the left side of your bike? Talk about a favorite memory? Thanks your body. to your brain, it’s possible to do all of these things. Your brain contains Protected by the skull, your brain is the mission 86 billion nerve cells, control center of your body. It may look like a called neurons, which giant wrinkly walnut, but it’s in charge of what send and receive you think, feel, learn and do. It never stops information. Those working—even when you’re asleep. messages zoom faster than a race car—at Your brain, your nerves and your spinal cord speeds of 268 miles make up your nervous system. The spinal cord is per hour (432 kph). the major nerve pathway that runs up and down your back. Messages whiz to and from the brain through nerves that branch off your spinal cord. The three main parts of the brain are the cerebrum, cerebellum and brain stem. The cerebrum—the largest part—controls your thinking, your memory and planned muscle movements. Located at the back of the brain, the cerebellum deals with coordination and balance. The brain stem connects your brain to your spinal cord. It helps your body perform important functions that you don’t usually think about, such as breathing, digesting food and pumping blood—all the things you need to live! By the time you’re 6 years old, your brain is 90% of its adult size. When fully grown, the brain weighs about 3 pounds (1.4 kg) and is about as big as a large grapefruit. 28 POPUL AR SC IENCE KIDS

Cerebrum Your brain isn’t really fully formed until you’re about 25 years old. Development begins from the back of the brain and heads toward the front. That means your frontal cortex— responsible for reasoning and planning—is the last part of the brain to become mature. Brain Stem you don’t say! Research shows that when you doze off in a new place, like a first sleepover at a friend’s house, your brain stays half awake. Called the first night effect, this is why you often feel tired the next day. Cerebellum 29

THE HUMAN BODY what’s going on inside your body? T hat slice of pizza sure tastes good! Food is fuel for your body. It helps keep your body going—just like a car. But what happens after you swallow it? The pizza takes a journey through your digestive system. First, the food has to be broken down into tiny parts called nutrients. Those nutrients give your body energy so it can do its job and keep you strong and healthy. how long does it take to digest a meal? See the time it takes for humans to fully digest their food, compared to other creatures. Person Sloth Hummingbird Giant Panda about up to about about 15–72 hours one month 10–20 minutes 5–13 hours

is your small intestine 10 really that small? FASCINATING At about 22 feet (6.7 m), the small intestine is FACTS ABOUT about four times longer than the large intestine. YOUR BODY They are named for their width—the small intestine is narrow, while the large intestine is wide. 1/ Every second, your body produces 25 million As you chew, your new cells. teeth break apart food, which mixes 2/ It takes food four to eight with saliva to make seconds to travel down it easier to swallow your esophagus. and digest. 3/ An adult’s stomach can Food travels down expand to more than 12 your esophagus, times its regular size after a tube that goes eating a meal. to the stomach. Muscles push the 4/ The thigh bone, called the food along. femur, is the longest bone in your body. In the stomach, acids break food 5/ The smallest bone— into a liquid called the stirrup—is located in chyme, which your ear. travels into the small intestine. 6/ Each day, your lungs breathe in about What’s left then 20,000 times. moves into the large intestine. It 7/ The tongue is like a comes out as waste fingerprint: No two are alike! when you go to the bathroom. 8/ People are the only animals with chins. 9/ There are between 2 million and 4 million sweat glands in your body. 10/ Our fingernails grow three times faster than our toenails. 31

THE HUMAN BODY how does your heart work? Your heart is a powerful muscle WORDS located between the lungs in the middle of your chest. As the arteries tubes that carry blood center of your circulatory system, away from the heart to other parts your heart pumps blood through a of the body network of blood vessels made up of arteries, veins and capillaries. capillaries the smallest blood Your blood carries oxygen and vessels, which move blood between nutrients throughout your body arteries and veins and gets rid of waste. veins tubes that carry blood back to About the size of a fist, the heart the heart from other parts of the body has two sides that pump blood. The right side receives blood that’s low in oxygen from your body. It pumps the blood to your lungs to get more oxygen. The left side then pumps the oxygen-rich blood around the body. The heart has four chambers—two on each side—that do all this hard work. The upper chambers are called the atria and the lower chambers are called ventricles. In less than a minute, your heart pumps blood to every cell in your body. you don’t say! Lub dub, lub dub. That’s the sound of a healthy heartbeat. The sound comes from your heart valves closing. The valves act like doors, controlling the flow of flood and preventing it from moving backward. 32 P O PU L AR SC I E N C E K I DS

This diagram of 10 blood vessels shows the INCREDIBLE FACTS arteries that TO GET YOUR carry blood away from the heart in HEART PUMPING red and the veins that bring it back 1/ Your heart beats about 100,000 in blue. times a day, or 37 million times a year. 2/ Your left lung is smaller than your right lung because it shares space with your heart. 3/ Your heart pumps about 2,000 gallons (7,570 liters) of blood around your body every day—enough to fill about 50 bathtubs. 4/ Your body contains about 60,000 miles (96,561 km) of blood vessels. If you lined them all up, they would circle the Earth more than twice. 5/ Blood leaves the heart through the aorta, which is the body’s largest and main artery. 6/ Most capillaries are thinner than a single hair. 7/ In one day, your blood travels more than three times the distance across the United States from coast to coast. 8/ Your blood makes up about 8% of your body weight. 9/ A blue whale has the biggest heart on the planet, weighing roughly 400 pounds (181 kg). That’s about 640 times the weight of a human heart. 10/ An infant’s resting heart rate ranges from 80 to 160 beats per minute. By the time you reach age 12, that rate goes down to between 60 and 100 beats. 33

THE HUMAN BODY how do your senses let you experience the world? Taste I magine it’s a sunny summer day on the beach. You feel the warm, Your tongue has tiny bumps that squishy sand run through your toes. contain taste buds. They enable You hear the waves splash against you to detect flavors that are salty, the shore. You smell the sunscreen sweet, sour, bitter and savory. Your slathered on your body. You see taste buds work with your sense of seagulls soaring overhead. You smell to give food its flavor. taste sweet, refreshing ice cream as it drips down the cone. Without By the Numbers An adult tongue your senses, you wouldn’t be able to has about 2,000 to 4,000 taste experience any of this. buds; they get replaced about every one to two weeks. You have five senses, all controlled by your brain: sight, taste, smell, you don’t say! hearing and touch. Your five main sense organs are the eyes, tongue, It’s a myth that the tongue has nose, ears and skin. different taste zones. All the tastes can be sensed on all parts, although the sides are most sensitive. Hearing Sound waves carry noises to your ears. When the waves hit your eardrum, it vibrates. Those vibrations are sent to three small bones in your middle ear that amplify the waves and pass them to the snail-shaped cochlea, a tube in your inner ear. Inside the cochlea, hair cells convert the vibrations to electrical signals, alerting your brain to the sound. By the Numbers You are born with 15,000 hair cells in the cochlea of each ear. 34 POPUL AR SCIENCE KIDS

you Sight don’t say! When light enters your eye, it hits the retina (a layer of light-sensitive Your senses not cells at the back of the eye) and only help you an image gets transmitted—upside make sense of the down. Electrical signals sent to world but also your brain through the optic nerve protect you from flip the image so you are able to danger. Your ears see it right-side up. hear a fire alarm By the Numbers Most people blink ring. You move about 15 to 20 times a minute, or up your hand away to 19,200 times a day while awake! when you touch something hot. Smell And your eyes let you know when As you breathe, your it’s safe to cross nose traps smells from the street. the air. Nerve cells in your olfactory bulb (underneath the front of your brain, just above the nasal cavity) let your brain know what you are smelling. By the Numbers Your nose has more than 400 kinds of scent receptors. They are able to detect at least a trillion different odors. Touch Your skin is made up of three layers: the epidermis (outer), dermis (middle) and subcutaneous tissue (the deepest layer). When you touch something, cells under your skin send messages to your brain. By the Numbers Every minute, your body sheds 30,000 to 40,000 dead skin cells. 35

THE HUMAN BODY Different parts of the body block what out germs, but are some sometimes they are ways we still able to sneak in. When they defend do, your body’s against immune system works like an army, disease? fighting off these harmful invaders. T hroughout history, different innovations— Every day you everything from new medicines come in contact to new technology—have with billions of helped us defend against germs—including illness. Vaccines are a kind of viruses—so tiny medicine that protect the body that they can only from disease. In 1796, the first be seen under vaccine was created to help a microscope. fight a disease called smallpox. Find out how vaccines work with your immune system. what are Late 1800s 1928 1945 some famous Doctors use the The first The first medical discovery of antibiotic, vaccine to advances? X-rays to see penicillin, fight the flu is discovered. bones in the body. is given. 36 POPUL AR SC IENCE KIDS

Typically, When you get a 6 vaccines contain cough or fever, either a dead your immune MIND-BLOWING or weakened system may be MEDICAL FACTS virus. COVID-19 battling a virus. vaccines use Colds, the flu and 1/ Ancient Egyptians applied honey to a material to COVID-19 are all wounds to protect from infection. create proteins caused by viruses. that trigger a 2/ Early toothbrushes, invented in China response from in 1498, used hair from hogs’ necks for the the immune bristles, which were attached to handles system. made of bone or bamboo. 3/ In the mid-1800s, the discovery of germ theory—the idea that disease can be caused by organisms invisible to the eye—eventually led to safer surgeries. Doctors began cleaning surgical tools with antiseptics to keep people safe. 4/ Ultrasounds use sound waves to take pictures inside the body and let doctors monitor babies during pregnancy. 5/ During robotic-assisted surgery, doctors control the instruments from a computer station—which allows for more precision. 6/ A scientist invented a new kind of surgical tape that was developed by studying how the tiny hairs on a gecko’s feet help it cling to surfaces. 1952 1954 1977 2020 Dr. Jonas Salk develops The first MRI is Vaccines are the polio vaccine to organ transplant invented developed to fight a virus that can takes place with to take pictures help control the cause paralysis. in the body. coronavirus pandemic. a kidney. 37

THE HUMAN BODY whydoes your body do these things? A CHOO! From sneaky sneezes to big burps, your body makes some weird noises. But there are important reasons for them. When you sneeze, it’s your body’s way of keeping you healthy by getting rid of whatever is bugging your nose. That can be anything from dust to dog hair to viruses. If your nose is irritated, nerves tell your brain that something needs to come out. As a result, air—along with mucus and saliva—is pushed from your lungs and out your mouth and nose. Lots of muscles work together to blast out a sneeze at incredible force. Tiny droplets from a sneeze can land up to 27 feet (8 m) away—farther than the length of a dump truck! To avoid spreading germs, use a tissue. If you don’t have one handy, sneeze into your elbow. 4 SURPRISES you don’t say! ABOUT SNEEZES Hiccups happen when something causes 1/ A sneeze is so powerful that it can your diaphragm—the dome-shaped muscle travel 100 miles per hour (161 kph)—as between your chest and stomach—to spasm. You fast as winds in a hurricane—and spray then suck in air quickly and your vocal cords snap about 100,000 germs. shut, creating the “hic” sound. Hiccups can occur after eating too much or drinking soda, when 2/ Bright sunlight causes about one in you’re chewing gum or if you’re nervous or excited. three people to sneeze. 3/ People may sneeze several times in a row, for an extra boost, to get out particles trapped in their nose. 4/ The award for the sneeziest animal goes to the marine iguana. It sneezes to get rid of salt after eating algae that grow in the ocean. 38 POPUL AR SCIENCE KIDS

why are some farts so noisy? People toot about five to 15 times a day, and some farts are noisier than others. Farts are gas in your intestines that come from air we swallow, mixing with bacteria. Hydrogen sulfide—a substance emitted from the bacteria—gives your farts a stinky smell. Some foods, like beans, onions, eggs and meat, release more gas as they break down—and can make the smell stronger. The sound depends on how much gas is inside you, how fast it comes out and the tightness of the muscles at your bottom. why do we yawn? Everybody yawns. Babies yawn before they’re born. Most animals do it too—even fish. You often yawn if you’re bored or sleepy. When you’re tired, research shows, the temperature of your brain increases. Some scientists think people yawn to pump air to the brain, helping it cool down, but no one knows for sure. While the mystery continues, one thing seems apparent: Yawning is contagious. Did looking at the photos on this page make you yawn? People often yawn after seeing, hearing or even reading about it.

THE HUMAN BODY what is your largest organ? Believe it or not, your body’s biggest organ isn’t inside of you. It’s your skin! Your skin acts as a protective barrier against germs and injury, and it regulates your body’s temperature. It’s thickest on the soles of your feet and palms of your hands and thinnest on your eyelids. If you spread out an adult’s skin, there would be about 22 square feet (2 sq m) of it—enough to cover a double bed. what is the hardest part of your body? Your teeth are covered in a tough outer layer called enamel. It’s the hardest part of your body, even harder than your bones. Tooth enamel protects the inside of your teeth. By the age of 3, most kids have a set of 20 baby teeth. As you grow, permanent teeth come in to replace your baby teeth. By adulthood, you should have a total of 32 teeth. what part of your body has the most bones? Let’s hear it for your hands—and feet! The bones there are part of your skeleton—the framework that supports your body, gives it a shape and protects your organs. You were born with about 300 bones. They fuse together, as you grow, into 206 bones. More than half are found in your hands and feet. There are 27 in each hand and 26 in each foot. 40 POPUL AR SCIENCE KIDS

which of your bones are most likely to break? Kids often break bones from falls—like off a bike—or while playing sports. The most commonly broken bones are the collarbones (clavicles) and the arm and wrist bones. They tend to break more than leg bones because you tend to throw out your arms to brace for a fall. where is your largest muscle? In your rear end! You have more than 600 muscles that enable you to move, digest food, pump blood and even breathe. The largest— the gluteus maximus—helps you stay upright, stand after sitting and climb stairs. which organ can grow back if it’s partially removed? Amazingly, the liver—the largest internal organ—can grow back if part of it is removed due to injury or disease. From processing nutrients in food to cleaning your blood, the liver performs hundreds of jobs. 41

CHAPTER 3 INVENTIONS How can we make that easier? How can we do it better? How can we solve this problem? Curious and creative people have been asking— and answering—questions like these for thousands of years. These inventors have built machines or devices, discovered new ways of doing things and created innovative ways to make life better. Inventing is hard work—there’s often years of trying and failing before a success. But thanks to the determination of inventors, the world is a much better place. Before there were movie projectors, Edison patented the Kinetoscope. People could watch a short motion picture by peering inside the box.

American inventor Thomas Alva Edison secured more than 1,000 patents for his inventions. Among the many things that came out of his labs (like the one pictured below) are the electric light bulb, the record player (phonograph) and a type of motion picture projector.

INVENTIONS 2/ Brainstorm Inventors often have to try many howdo different ways to solve new things the problem before they get invented? hit on the one that might work best. S ince humans started having problems, people have been coming up with new ways to solve them. The steps to bring something new into the world are pretty much the same, whether you are carving the first wheel or inventing the latest VR device. 1/ Find a Problem to Solve Any new invention needs to figure out an existing problem or complete a task better than it is being done now. So identifying this problem or opportunity is the first step. 3/ Build a Prototype For inventions with a shape or form, such as machines and devices, inventors build a single working model called a prototype.

4/ Start Testing how do That prototype is then companies tested over and over, invent to make sure it works things? in all conditions. A lot of famous inventions 5/ Obtain a Patent were the hard work and Once the prototype inspiration of one persistent works for sure, the person. But other things inventor applies for that are part of our lives a patent. This is a came from a group of formal document experts, working together. that proves who Apple has created dozens owns the invention. of personal devices and Then it’s time to computers, but these were figure out how to not the inventions of one make lots more of person. Instead, engineers, the new invention. designers and computer experts worked together. Each brought their specialty to the problems posed by Apple co-founders Steve Jobs and Steve Wozniak. From this creative teamwork came the Macintosh computer (1984), PowerBook (1991), iPod (2001), iMac (2006), iPhone (2007), Apple TV (2007), iPad (2010) and Apple Watch (2015). Most of those devices have been updated and improved since their invention, through a series of new designs and upgrades— all thanks to teamwork. 45

INVENTIONS howdid human beings learn to fly? F or centuries, when people looked up and saw birds, some wondered, “Why can’t we do that too?” The dream of flight finally came true in 1903, with the invention of the airplane by American brothers Orville and Wilbur Wright. They successfully combined wings modeled after those of birds with the power of a gasoline-motor-driven propeller. Their discovery kicked off what has become more than 100 years of new ways for humans to fly.

The Wright Flyer takes off 5 (left); you can see it today at the National Air and Space FAST FACTS Museum in Washington, D.C. YOU MAY NOT KNOW ABOUT FLIGHT 1/ In a hot air balloon, flyers ride in a basket that hangs beneath a huge balloon filled with air that is heated, making it more buoyant. 2/ You can ride on air currents while strapped beneath the wings of a hang glider before reaching a safe landing. 3/ The rotating blades of a helicopter enable these craft to hover in place. Copters can also fly forward or backward. 4/ The world’s fastest jet aircraft was the SR-71 Blackbird, which topped 2,100 miles per hour (3,380 kph). It is on display at the National Air and Space Museum in Washington, D.C. 5/ In 1895, Peruvian engineer Pedro Paulet experimented with high- powered engines using liquid fuel. He also designed aircraft that could use these engines. Paulet’s craft didn’t fly—but without his ideas, we’d still be looking at the moon instead of walking on it. 47

INVENTIONS when did a book lead to a popular invention? I n 1968, scientist Spencer Silver was determined to make a sticky, strong glue, but his efforts resulted in glues that hardly stuck at all. Maybe he was on to something, but he didn’t know what. Years later, a co-worker needed a bookmark that wouldn’t slip out of his book. The light bulb went off and, a decade after Silver accidentally developed the low-tack adhesive, Post-it Notes were everywhere. who 1946 invented these things Microwave Oven we couldn’t live Percy Spencer without? 1914 Electric Refrigerator Florence Parpart 1903 1946 Car Windshield Wipers Disposable Diapers Mary Anderson Marion Donovan 48 POPUL AR SCIENCE KIDS

how did a mechanical engineer revolutionize medicine? German scientist Wilhelm Rontgen was experimenting with cathode ray light (a stream of electrons in a glass tube) in 1895. As he projected it onto glass, an odd green light leaked out. Intrigued, he tried projecting these rays onto other things. Eureka! The light made pictures of what the rays passed through. He didn’t know what he’d discovered, so he called them X-rays. He earned a Nobel Prize in Physics for his invention. 1969 1989 Home Security System World Wide Web Tim Berners-Lee Marie Van Brittan Brown 1994 Smartphone Apps IBM 1961 Computer Chip Jack Kilby and Robert Noyce 49

INVENTIONS how do things get invented by accident? M ost inventions are the result of patience and planning, testing and retesting ideas until one finally works just right. Inventions can take years or decades to come to life. But some famous products were invented by accident. Inventors who were looking for one thing suddenly found another. The key, of course, is that they recognized that their “mistake” was really a big breakthrough! what accidental invention has saved many lives? Athletes in many sports know that a helmet is important for their safety. Many helmets use a superhard type of carbon-based fiber called Kevlar. It was invented by American chemist Stephanie Kwolek in 1966. But Kwolek was actually trying to perfect a lighter fiber for car tires. Instead, she invented a new method of spinning plastic fibers that created the rock-hard stuff. 50 POPUL AR SC IENCE KIDS