Saturday 27 June 2009

Oxygen


If an astronaut strikes a match in space, nothing happens. On Earth the tip bursts into flame because it reacts with a gas that is part of the air. That gas is oxygen.

WHAT IS OXYGEN?
Oxygen is invisible and has no smell, but it makes up about a fifth of the air around us. Oxygen is an element. Elements are basic substances that combine to form all the materials found on Earth. Water, for example, is a combination of the elements oxygen and hydrogen. Rust is oxygen combined with iron. Oxygen is the most common element on the planet. Almost half the
weight of Earth’s crust is oxygen, but the oxygen is combined with other elements in rocks.

LIFE NEEDS OXYGEN
Except for a few kinds of bacteria, all living things need oxygen. Without it they would die. Animals that live on land breathe oxygen from the air into their lungs. You are doing that right now. Plants that live on land take in oxygen through tiny openings in their leaves. Insects have tiny holes in their shells that allow oxygen to seep in. Animals and plants that live underwater absorb oxygen that is dissolved in water. Oxygen gets recycled from plants to animals and back again. Green plants combine the Sun’s energy with water and carbon dioxide to create food for themselves. In the process, the plants produce oxygen and release it into the air. Animals, including humans, breathe in the oxygen. Animals breathe out carbon dioxide. Plants use the carbon dioxide to make more oxygen.

HOW DO WE USE OXYGEN?
Anything that burns needs oxygen. When wood burns, it is actually combining with oxygen. The flame of a candle or a gas stove is produced by oxygen combining with other elements. Fossil fuels such as oil, coal, and natural gas also need oxygen so that they can burn. Burning, a process known as combustion, produces heat. We use the heat to keep buildings warm, cook food, produce electricity, and move our cars and trucks. Animals use oxygen to keep their bodies working and to move around. Their muscles need oxygen for energy. Hospitals give oxygen to patients who are short of breath. Some pilots and mountain climbers need to breathe oxygen from special tanks in order to travel at high altitudes where the air is too thin to breathe. Divers need tanks containing oxygen so that they can spend time exploring underwater.

Oil


What would our world be like without oil? We wouldn’t have gasoline-powered cars. We wouldn’t have airplane fuel or oil to heat our homes. Many paints, fertilizers, and kinds of cloth are made partly from oil. So are many plastics, chemicals, building materials, and even medicines. It’s hard to imagine life without oil. Yet the world’s supply of this valuable resource is running out.

WHAT IS OIL?
Oil is the purified form of a black or brown liquid called crude oil. Crude oil is a mixture of substances called hydrocarbons. They’re called hydrocarbons because they are made up of the elements hydrogen and carbon. Hydrocarbons give off a lot of energy when they burn. That’s why they make good fuels. They also can be combined with other elements in many ways to make different products. Crude oil forms under Earth’s surface. It forms from the remains of sea animals and plants. (This is why oil is called a fossil fuel—it comes from fossils.) When these living things die, they sink to the sea bottom. Over millions of years, they form a thick layer. The layer can get buried under sand and rock. Pressure and high temperatures inside the planet change it into oil and natural gas.
Most crude oil is trapped far underground. But it seeps through to the surface here and there, forming pools of black liquid. People have known about these pools for thousands of years. In the 1850s, chemists began to discover different ways crude oil could be used. These discoveries set off a massive search for oil. This search is still going on today.

EXPLORING FOR OIL
Scientists and engineers explore for crude oil beneath the ground. They look for particular kinds of rock and land features on Earth’s surface. They explore underground with sound waves. But there is really only one way to prove that crude oil is present. You have to drill an oil well. Only about one-third of wells dug for exploration strike oil. The rest turn out to be “dry.” More oil sources have been found by lucky guesses than by science. Oil wells don’t keep pumping until the crude oil is all gone. Less and less oil comes up as a well begins to go dry. A well is only useduntil it costs more money to get the oil out than the oil can be soldfor. At that point the well is capped.

REFINING CRUDE OIL
To be useful, crude oil must be cleaned and purified. Then it must be separated into different substances. This process is called refining. Crude oil is refined at huge factories called oil refineries. Gasoline, fuel oil, asphalt, waxes, and other hydrocarbons can be separated from crude oil at various temperatures. Then, they can be processed for different uses.

A NONRENEWABLE RESOURCE
Oil is a nonrenewable resource. The supply is limited. It takes millions of years for oil to form. Once oil is used up, it’s gone. Nobody worried about this problem 100 years ago. But the world is
using more oil each year. Today, oil supplies about two-fifths of the energy used in the United States. Americans use about 700,000,000 gallons of oil every day (about 2,650,000,000 liters).
About two-thirds of it is used as fuel for cars, airplanes, trains, and other vehicles.

New sources of crude oil will probably be discovered. So will new ways of draining the last drops of oil from known sources. Even so, most experts agree that the world’s oil reserves will be largely gone by the year 2050.

Lighthouses


Lighthouses are tall buildings near seacoasts. They shine flashing lights at night or in foggy weather. These lights guide ships that sail close to the coast. Many lighthouses also have foghorns to guide ships in foggy weather. Lighthouses are built at places on a coast that are important to ships. They warn ships of hard-to-see dangers such as rocks or strong currents. They also mark entrances to harbors or rivers. Most lighthouses are painted white so thatthey can be seen easily during the day.

WHEN WERE LIGHTHOUSES FIRST BUILT?
Lighthouses have been protecting sailors for thousands of years. Lighthouses were built on the coast of the Mediterranean Sea at least as long as 2,600 years ago. One of the so-called Seven Wonders of the World was an enormous lighthouse called the Pharos, built at Alexandria in Egypt. Ancient lighthouses were simple structures. Fires burned on top of them as signals to ships.

LIGHTHOUSE KEEPERS
Until fairly recently, many lighthouses had lighthouse keepers living in them. The job of the lighthouse keeper was to make sure the lights were kept in working order at all times. Sometimes the lighthouse keeper’s family lived in the lighthouse, too. It was lonely living in a lighthouse in an out-of-the-way place. The lighthouse keepers might not see any other people for weeks. These days, lighthouse keepers are no longer needed. The lighthouses work automatically.

LIGHTING A LIGHTHOUSE
Lighthouses of the past were lit by burning coal or wood. In the late 1700s and 1800s, oil lamps became popular. Many lighthouses burned whale oil, especially lighthouses in the United States. In the late 1800s, lighthouses began to burn gas in their lamps. Lighthouse keepers were needed to keep fires burning and clean up soot the fires created. Today, most lighthouses use high-power electric lights that rotate. Reflecting mirrors and lenses make the light beam stronger. The lights work much like the lamp on top of a police car, but they are much bigger and more powerful.

Glass


Glass is a wonderful substance. It’s hard and firm, yet we can see through it. Glass can protect us from the wind and the rain. But it lets sunlight through, which is useful for keeping our homes light and bright. Glass is also brittle, which means it breaks easily. But there are ways to make it
strong.

HOW IS GLASS MADE?
Glass is made by melting silica, a chemical that comes from sand. At extremely high temperatures, silica melts and becomes liquid. Other substances are usually added to the melted silica to make the glass strong. In its liquid state, glass can be molded into different shapes. Glass was first made at least 4,000 years ago. About 2,000 years ago, people in the Middle East discovered that molten (melted) glass could be blown into different shapes. They put a gob of glass on the end of a metal tube. Then they blew air through the tube. The glass at the end of the tube expanded, just like a balloon. Glass blowing remained the usual method for making glass vessels until the early 1900s. In 1903, an automatic glass blowing machine was invented. Glass can also be made into sheets that are flat and smooth. It can be shaped in molds. Substances can be added to glass to give it color. And once glass is cold, it can be decorated by cutting and
painting. Glass can be recycled. It is sorted by color and then melted in big furnaces. The molten glass is formed into new shapes.

HOW IS GLASS USED?
Glass is quite cheap to produce because it is made from sand. Glass is used for making everyday items such as windows, bottles, and drinking glasses. Many beautiful objects are made of glass. Artists have produced elaborate shapes and elegant designs in glass. Stained-glass windows in churches are made of pieces of colored glass. The pieces are fitted together to form a picture. Glass can be made strong enough to stop a speeding bullet. Bulletproof glass is made by layering sheets of glass with sheets of plastic. Car windshields are made of shatterproof glass. They crack
rather than shatter if they are hit. This makes them much safer.

Colds and Flu


You start sneezing. Your throat gets sore and scratchy. You have to blow your nose a lot. You don’t feel very well. Do you have cold? Or do you have the flu? Colds and flu are illnesses caused by germs. They are both caused by germs called viruses. But they are caused by different kinds of viruses. Colds are often called common colds. Flu is short for influenza.

IS IT A COLD OR THE FLU?
Signs that you have a cold or the flu are called symptoms. The symptoms of a cold and the symptoms of the flu are slightly different. The symptoms of a cold are sore throat, cough, sneezing, and a stuffy, runny nose. Colds usually do not cause a fever. Flu symptoms are like cold symptoms, but the flu also causes chills, fever, and headaches. It makes you feel tired and achy all over.
A cold or the flu usually lasts about a week. Every once in a while they can lead to a more serious sickness, such as an ear infection or a lung infection called pneumonia.

CATCHING A COLD OR THE FLU
People once thought you could catch a cold from getting a chill in cold weather. They thought that wet feet or drafts of cold air could give you a cold. We now know that germs cause colds and flu. The germs are passed from one person to another. They travel in coughs and sneezes. More colds and cases of flu happen in cold weather because people spend more time together indoors when it’s cold outside. It iseasier for germs to spread when people are close together.

IS THERE A CURE?
There is no cure for the common cold. People take medicine to help their sore throats, coughs, and runny noses. Doctors say that resting in bed is the best way to treat a cold. There is no cure for the flu, either. Doctors can give medicine to make you feel better. Resting in bed and drinking lots of juice and water is the best way to treat the flu.

AVOIDING A COLD OR THE FLU
You can get a flu shot to help keep you from catching the flu. A flu shot, or vaccination, helps your body fight off flu germs if they attack. But it doesn’t always work. The flu virus keeps changing. When it changes, the old vaccine no longer works. Doctors have to keep making new vaccines. For this reason, you need a new flu shot every year. Sometimes the flu changes enough in a single year that you can still catch it even if you’ve been vaccinated. There is no vaccine against the common cold because more than 100 different kinds of viruses cause colds. These viruses also keep changing.

One thing you can do to protect against cold and flu germs is wash your hands before you eat anything or touch your face. Your hands may pick up the germs from door knobs or other things touched by someone with a cold. Washing your hands thoroughly kills the germs. You can also try not to spread germs when you have a cold or the flu. Use tissues when you sneeze. Cover your mouth when you cough. And wash your hands frequently to keep from spreading cold germs to others.

Sleep and Dreaming


Dogs sleep, cats sleep, and you sleep. All mammals and birds sleep. Scientists are not sure if fish, reptiles, and insects sleep. Big animals sleep less, and small animals sleep more. Elephants and giraffes sleep only 2 to 4 hours a day. Bats, opossums, and armadillos sleep 18 hours a day or more! Even kids need more sleep than grownups. A newborn baby sleeps 17 to 18 hours a day. A 10-year-old needs about 10 hours of sleep a night. Grownups need between six and nine hours of sleep a night. Some people need more sleep than others.

WHY DO WE HAVE TO SLEEP?
Scientists do not know for sure why you sleep. They do have some ideas. Safety could be one reason for sleep. People and other animals might sleep because it keeps them safe at night. It’s hard to see in the dark. Enemies could sneak up and attack animals that are wandering in the darkness. Most mammals and birds go to trees, underground dens, or nests at night. Prehistoric people went into caves or other shelters. They covered up with furs and fell asleep. You go into your home at night and snuggle up in bed. Sleep might also help your body work better. Things go wrong if you do not get enough sleep. It is hard to think and work and play unless you get plenty of sleep.

WHAT HAPPENS WHEN WE FALL ASLEEP?
Scientists have learned a lot about what happens when you lie down, close your eyes, and fall asleep. They study people in sleep labs. ometimes your eyeballs move back and forth while you’re asleep. They move fast. Scientists call this kind of sleep REM sleep. REM stands for rapid eye movement. Your body may twitch during REM sleep. Your brain is also very busy during REM sleep. It is almost as busy as when you are awake. What do you think your brain is doing? Here’s a clue: You dream during REM sleep. There is another kind of sleep. Your eyeballs do not move. Scientists call this NREM sleep. NREM stands for nonrapid eye movement. Your brain is not very busy during NREM sleep. You go back and forth between REM and NREM sleep all night long.

WHY DO WE DREAM?
Scientists have done many studies on dreams. They think your senses may have a lot to do with dreams. In dreams, you see and hear things. Dreaming is not like thinking about things. You have feelings during dreams. You may feel happy or angry. You feel fear if you have a nightmare. Your memories may have something to do with your dreams. Dreams are often like stories that stop before they are finished.

DO DREAMS MEAN ANYTHING?
People in ancient times looked for meaning in dreams. The ancient Egyptians believed dreams could tell the future. Some psychologists think that dreams show what people feel deep inside. They ask people to talk about their dreams. Some scientists think that dreams have no meaning. They think that dreams just come from nerve signals in your brain. Other scientists think that dreams are important for memory. They may help your brain sort out what to remember and what to forget.

Microscopes


How is it possible for something right in front of your eyes to be completely invisible? It’s possible when that thing is too small to be seen with your eyes. We can see drops of water from a pond or lake. But we cannot see the thousands of tiny creatures that live in the water. Drops of blood contain tiny structures called cells, but we can’t see them either. Microscopes allow us to see invisibly small things.

Microscopes are one of the most important tools of scientists. Medical scientists use them to see the germs that make people sick. Biologists use them to see how plants and animals are constructed. Geologists—scientists who study the Earth—use them to find out what rocks are made of. Some microscopes are so powerful that they enable us to see individual atoms, the tiny building blocks of everything.

DIFFERENT KINDS OF MICROSCOPES
Some microscopes make tiny objects look larger using lenses that bend light rays. Microscopes that use light to look at small objects are called optical microscopes. The simplest optical microscope is a magnifying glass. The best magnifying glasses can make things look 10 to 20 times larger than they actually are. The optical microscopes used by scientists are called compound microscopes. They contain several lenses. The scientist looks through a lens called the eyepiece to see the magnified object. Compound microscopes often have three different settings. Each setting provides a different magnification. Optical microscopes can produce magnifications of up to about 1,000 times. To view even tinier things, scientists use microscopes called electron microscopes and scanning probe microscopes. An electron microscope shoots tiny particles called electrons at the thing being viewed. Instruments turn the pattern of scattered electrons into an image on a screen. The best electron microscopes can produce images with magnifications up to 1 million times. A scanning probe microscope uses an extremely tiny probe, or tip, to “feel” the surfaces of tiny objects. The end of the probe might have a width of just one atom. A scanning probe microscope can make images of the individual atoms on the surface of an object. Some scanning probe microscopes can magnify objects by as much as 100 million times.

WHEN WERE MICROSCOPES INVENTED?
Historians think the compound optical microscope was invented by a Dutch eyeglass maker, Zacharias Janssen, in the late 1500s. Most microscopes were not very good until the early 1800s. That is when lens makers first learned how to make lenses that produce really clear, sharp images. German scientists developed the first electron microscope in the early 1930s. The first scanning probe microscope was created by Swiss and German scientists in 1981.

Friday 5 June 2009

Lasers


Lasers are powerful enough to cut through steel. Lasers are delicate enough to use in eye surgery. Lasers “read” the information coded on compact discs (CDs). These are just a few things that lasers do.

WHAT IS A LASER?
A laser is a device that produces a beam of light and makes the beam more intense. A laser beam is very exact. It can travel a long distance without spreading out and losing its power. Laser light is unlike sunlight or light from a light bulb. To understand the difference, think of a crowded city street. Thousands of people are walking along the sidewalk. Their clothes are of many different colors. They are walking in many different directions. Now think of a marching band in a parade. Everyone is wearing a uniform of the same color. They are all walking in the same direction, in step with one another. Sunlight and light from lamps are like the crowd on the sidewalk.

They are made up of many colors—all the colors of the rainbow. They spread out in all directions from their source. Laser light is like the marching band. It is light of a single color. It travels in a
beam. It spreads out very little, even when traveling through outer space.

HOW ARE LASERS USED?
Because lasers produce such exact beams of light, they are very useful tools. Some lasers are so powerful they can drill holes in diamonds. These lasers can cut a piece of steel to an exact shape needed for a machine part. Powerful lasers can produce temperatures of 10,000° Fahrenheit (5500° Celsius) and higher. This ability makes them useful in factories for joining together large
pieces of metal. Much smaller lasers “read” price tags on products. At the supermarket, you’ve probably seen the checkout clerk run foods
over the laser scanner. Small lasers in compact disc (CD) players read the information coded on CDs. This information is then played back as music. Lasers even carry telephone conversations. Laser beams send thousands of telephone calls through thin glass threads called optical fibers. In hospitals, doctors use lasers for delicate operations such as repairing damaged eyes. The military uses lasers to guide airplanes and missiles. And laser beams are used to create colorful light shows. These are just a few of the ways we use lasers.

WHEN WERE LASERS INVENTED?
Famous scientist Albert Einstein first suggested the idea of a laser in 1917. In the 1950s, scientists began making the idea work. American scientist Gordon Gould suggested the name laser in 1957. It was short for Light Amplification by Stimulated Emission of Radiation. The first working laser was built in 1960. It was built by another American scientist, Theodore Maiman. The development of lasers advanced rapidly during the 1970s and 1980s. Scientists today are using a huge and powerful laser to study how atoms join together in the Sun to release energy. This laser was built at Lawrence Livermore National Laboratory in California. It takes up a building the size of a football stadium.

Hair


Hair is one of the things unique to the mammal world. Dogs, cats, lions, squirrels, and seals—they all have hair. So do humans. Hair grows only on mammals.

WHAT IS HAIR?
Hair is an extension of your skin. It’s made up of old skin cells that are filled with a protein called keratin. Pack a lot of these cells in a long, narrow line and you have a hair. Keratin is used to make fingernails, claws, scales, beaks, feathers, and other skin attachments, too. Each hair grows inside its own follicle. A follicle is a little pit in your skin. And hair grows at the root, not at the tip. That means that new hair is added to the bottom, or root, of the hair and the old hair gets pushed up. That’s why when dyed hair grows out, the dyed part gets pushed farther from the scalp and the real hair color appears at the bottom. In humans, hair comes naturally in black, brown, blonde, red, white, and various shades in-between. In animals, there are even more varieties and patterns of hair color. Markings such as a tiger’s stripes and a leopard’s spots come from differences in hair color. They are often how we quickly identify these animals.

HAIR HAS MUSCLES?
Yes! Each hair follicle has a tiny muscle called the arrector pili attached to it. When you’re cold or when you’re scared, the muscle pulls the hair up, making your hair stand on end. That’s what
goose bumps are: the muscles in your hair follicle pulling tight! Have you ever seen a cat hiss and arch its back? It’s the same thing. In animals, the raised hair makes the animal look bigger and
scarier than normal so that a would-be attacker might run away in fright.

THE JOB OF HAIR
Hair does a lot of other things, too, depending on the animal. When hair is real thick it’s called fur. Fur keeps an animal warm. Some animal fur is even valued by people because it is so warm.
Fur color can help an animal blend into its surroundings, allowing it to hide better. Some animals even change color with the seasons. The arctic fox, for example, is dark in summer but white in winter. This winter coat makes it hard to see the fox in the snow. Even the spines of a porcupine are modified hairs. Spines are just stiff, sharp hairs that protect the animal when attacked.
Hair also helps animals sense their surroundings. Longer hairs can brush against things to help animals orient their bodies. For example, whiskers are special hairs around the face that help an
animal feel its way around in the dark.

HAIRSTYLE
In humans, hair’s importance is mainly as decoration. Hair and beards have been a great part of dress and style for both men and women since ancient times. The way kings and queens wore their hair influenced the fashion of the day, the same way that a celebrity hairdo today can start off a hairstyle trend.

Dams


Beavers build them from sticks. Landslides create them from trees, mud, and debris. Humans make them from earth and concrete. These structures are dams. Dams hamper the flow of water in a river or stream. Landslides don’t mean to create dams. They do so by dumping a lot of earth and other stuff in a river. Scientists think beavers build dams for protection. Beaver dams capture water in front of the lodges in which beavers live. Beavers can hide from their enemies in this deeper water. A dam also protects the beaver lodge by slowing the river’s speed.

WHY DO WE BUILD DAMS?
We build dams to control water. A dam built across a river or stream stops the water’s flow. Water collects in a lake behind the dam. The lake stores water for people to use later. The lake, or water storage area, is called a reservoir. The water in reservoirs travels in pipes to people’s homes for drinking water. It can flow through canals for farmers to use in watering their crops. People also sail boats and swim in reservoirs. Many dams use reservoir water to produce electricity. Water flows into large machines called turbines inside the dams. The turbines power other machines that generate electricity. Electricity produced in this way is called hydroelectric power.Some dams are built to prevent flooding. During the rainy season, the reservoir stores the river’s extra water. During the dry season, the dam sends the reservoir water back into the river.

HOW BIG ARE DAMS?
If you’ve ever visited a large dam, you know it is an amazing sight. Dams are some of the biggest structures ever built. The Hoover Dam on the border of Nevada and Arizona is as tall as a 72-story building. The Grand Coulee Dam in the state of Washington contains enough concrete to build a sidewalk all the way around the Earth. Few dams are this big, however. Most dams are small structures less than 10 feet (3 meters) tall.

WHAT ARE DAMS MADE OF?
Many large dams are made of concrete. Some are made of packed earth or rocks. Because these materials are not as strong as concrete, dams made of earth or rocks must be very thick. The Tarbela Dam in Pakistan is made of earth and rock. It contains more than 15 times as much material as the Grand Coulee Dam.Dams must be strong enough to withstand the pressure of water against them. Dams also must be cared for and repaired. A dam that breaks can cause disaster. In 1889, a dam in Pennsylvania broke and let loose a wall of water. The water submerged the town of Johnstown, knocking down houses and killing more than 2,000 people.

Bows and Arrows


Thousands of years ago, human hunters had a problem. They couldn’t get close enough to an animal to use spears or knives to bring down their prey. Finally, they found a clever solution: the bow and arrow. No one knows just how or when the bow and arrow was invented. Some experts say it was developed more than 25,000 years ago. No matter when it appeared, it changed hunting and warfare for good. Using a bow and arrow, humans could strike at animals and enemies from a long distance away and with more accuracy. People didn’t have to get so close that they might be killed first.

THE BOW AND ARROW IN WARFARE
The bow and arrow was a valuable weapon for many armies. The ancient Egyptians were the first people known to have used the bow widely in war. The Romans, Chinese, Persians, and other civilizations also used the bow and arrow against their enemies. During the 400s AD, the Huns from Asia rode into Europe on horseback. The Huns terrorized Roman armies with powerful composite bows. Composite bows consisted of several materials glued together, which made the bows more elastic. These bows were shorter than standard bows and handier to use when fighting on horseback. They could kill with great accuracy from up to 300 yards (275 meters) away. That distance is as long as three football fields! In the 1200s, another Asian people, the Mongols, also made great use of the composite bow. The longbow is one of the most famous bows in history. English bowmen used it with great skill. An arrow from a longbow could
pierce a knight’s armor or kill his horse. The legendary English hero Robin Hood was said to be so skilled a bowman that he could split one arrow with another arrow. The longbow required strength, but it could fire an arrow hundreds of yards with great accuracy and force. England fought a lengthy war with France in the 1300s and 1400s. During battle, thousands of arrows shot from English longbows rained down on French knights in armor, killing many.

By the 1500s, armies had started to use guns in warfare. As guns got better, they completely replaced the bow and arrow. But bows were still used in some parts of the world. Native Americans fought against white settlers with bows and arrows. The Great Plains Indians had powerful bows that could fire an arrow all the way through a buffalo at close range.

THE BOW AND ARROW IN SPORT
Today, people no longer use the bow and arrow in warfare. But they do use it in hunting and in the sport of archery. Many states and Canadian provinces have hunting seasons for archers to hunt animals with a bow. Archers also take part in sports competitions. Archery is an event in the Olympic Games. Some modern bows are still made of wood. Others are made of carbon or fiberglass, which makes them lighter and more flexible. The compound bow has a system of cables and pulleys attached to it. The cables and pulleys make it easier to pull back the bowstring, allowing the arrow to go farther. Most arrows today are made of aluminum, fiberglass, or carbon fibers. The fletching, or feathers, on the end of the arrow may be made of turkey feathers or plastic. Fletching makes an arrow flystraight after leaving the bow.

Robots


When you think about robots you may imagine metal machines from science fiction that look a lot like people. There are already almost a million robots at work in the world. Almost none of them look like the robots in science-fiction movies. Robots are machines. They are machines that are controlled by computers. Robots do work. You probably would not like to do the work that robots do. Some robots do jobs that are dangerous. Some robots do jobs that are boring. They just do the exact same thing over and over again. Robots that do these jobs are called industrial robots. Almost all robots in use today are industrial robots.

WHAT DO INDUSTRIAL ROBOTS LOOK LIKE?
Most industrial robots are just mechanical arms. Robot arms can bend. Some robot arms bend like an elephant’s trunk. Some robot arms can make themselves longer or shorter. Many robot arms have parts on the end that can hold things. The parts are called grippers. They work like a human hand, but they often don’t look much like a hand. Special kinds of grippers can handle tools or move things around.

HOW DOES A ROBOT ARM MOVE?
Your muscles move your arm. Electric motors move a robot’s arm. A robot arm has joints that allow it to bend just as your arm does. Your arm has shoulder, elbow, and wrist joints. A robot arm can have as many joints as it needs to do its job. A computer figures out how the robot’s arm and gripper should move. The computer sends signals to the electric motors. Some robot arms have sensors. The sensors tell the computer where the arm is. The computer makes the motors move the arm if it is not in the right place.

WHAT KINDS OF JOBS DO ROBOTS DO?
Robots do things over and over in exactly the same way. The robots can move quicker than humans can, and they never get bored. Most robots are designed to do only one specific job. A different robot must be specially made for each job that needs to be done. Many robots work in plants that make automobiles. Robot arms weld metal car parts together. They spray paint on cars. Other robots work in factories that build radios, TVs, computers, and other electronic products. Some robots help doctors do operations. Robots help replace hips. They help doctors operate on eyes. Some robots handle chemicals that are dangerous for humans to touch. Some robots go to dangerous places. Robots can go deep underwater to search for sunken ships or look for minerals to mine. Robots can go into active volcanoes. Robots help explore Mars and other planets. They find out what the planets look like and what they are made of. Robot rovers that look like little wagons landed on the planet Mars. They rolled around and examined the rocks and soil.

WILL ROBOTS EVER BE LIKE HUMANS?
Scientists and engineers are working to make better robots. They are trying to make robots with computers that are smarter. They are trying to make robot legs that walk. It is very hard to make a machine that can walk on two legs the way you can. One day there will be robots that make highways and build steel skyscrapers. Inventors are starting to make robots for use at hometo clean carpets and mow lawns. There may someday be robots that help with many chores around the house. Tiny robots may one day be able to go into clogged blood vessels and clean them out. Tiny robots may be able to go inside broken machines and fix them. Very smart robots may eventually be able to run a whole factory by themselves.

Plastic


What is as hard as stone, strong as steel, clear as glass, light as wood, and springy as rubber? Plastics can be like all of these things. Plastics are materials used to make a wide variety of products. Plastics cost less than many other materials. Plastics do not rot like wood. They do not rust like metals. Plastics can be any color. You use plastics everyday. Your computer case is made of hard, strong plastic. You drink out of cups made of light plastic foam. You wear clothes and walk on carpets made of plastic threads. You buy food and other goods covered in clear plastic wrap. Plastic is everywhere around you.

WHERE DOES PLASTIC COME FROM?
Plastic comes mainly from fossil fuels. Oil, coal, and natural gas are fossil fuels. The building blocks of fossil fuels are the chemicals hydrogen and carbon. Like all chemicals, hydrogen and carbon are made from atoms, tiny bits of matter much too small to see. Everything is made of atoms. You make plastic by heating fossil fuels and adding other chemicals. The hydrogen and carbon atoms link together. The atoms join together like beads on a string. The long chains of atoms are what make plastics special. Metal, glass, wood, and clay are made of short chains of atoms.

MOLDING PLASTIC
Plastic starts out as a hot, sticky goo, called resin. The resin gets made into car parts, compact disks, plastic bottles, and all the different kinds of plastic products. To make plastic products, the heated resin is poured or forced into a mold. The resin cools and hardens into the shape of the mold. In fact, the word plastic comes from Latin and Greek words that mean to mold.

DOES PLASTIC HARM THE ENVIRONMENT?
People in the United States throw millions of tons of plastic away every year. Plastics do not easily break down, or degrade. Plastics fill up garbage dumps, called landfills. Plastics are a major source of pollution. Using less plastic helps reduce the amount of plastic waste. Making thinner plastic bottles and other containers uses less plastic. Many plastics can be recycled, or reused. Recycled plastics are used to make new plastic products. Recycling reduces the amount of plastic that gets dumped in landfills.

Nuclear Weapons


First you see a blinding flash of light, brighter than the Sun. Moments later, a huge ball of fire appears, brilliant orange. The fireball begins to rise into the sky. Soon it widens at the top and is shaped like a mushroom. A thundering sound and blast of heat reach you 15 miles (24 kilometers) away. You are seeing the explosion of the world’s first nuclear weapon, on July 16, 1945, in a New Mexico desert.

WHY DO WE HAVE NUCLEAR WEAPONS?
Nuclear weapons are the most destructive weapons ever made. Building a nuclear weapon was a top-secret project during World War II. Scientists had been working on this weapon—the atomic
bomb—for three years by 1945. Almost nobody else, except the president of the United States, knew about this work. The secret effort to build a nuclear weapon was called the Manhattan Project. By 1942, when the Manhattan Project began, Germany had conquered much of Europe and was out to conquer the rest. The United States had just joined the war. The United States and its allies were afraid that Germany would develop an atomic bomb first. Then Germany would win the war. The United States and its allies had to beat Germany to the bomb. Germany had already surrendered by the time the atomic bomb was ready. But Japan was still fighting the war. To end the war quickly, the United States dropped two atomic bombs on Japan. The bombs killed at least 100,000 people and destroyed the cities of Hiroshima and Nagasaki. Japan surrendered soon afterward. The nuclear age had begun.

WHY WAS THERE A NUCLEAR ARMS RACE?
The nuclear arms race was a buildup of nuclear weapons after World War II. When the war ended, scientists knew that it was possible to build nuclear bombs far more powerful and destructive than the first atomic bomb. Some people, including scientists, thought it was wrong to build these weapons of mass destruction. Others feared that the Soviet Union would make them first. By the late 1940s, the Cold War pitted the United States and its allies against the Soviet Union and its allies. Each side feared an attack from the other side, though their armies did not actually fight during the Cold War. Everyone knew that a war using nuclear weapons would be a terrible disaster. A nuclear war would kill millions of people and possibly end life on Earth. Each side believed that having a large supply of nuclear weapons would frighten the other side and stop it from starting a nuclear war. If one side attacked, the other side would strike back with even more nuclear bombs. And so began a race to have more nuclear weapons than the other side. Luckily, no nuclear attacks happened after World War II.

HOW DO NUCLEAR WEAPONS WORK?
A nuclear weapon gets its name and its explosive power from the nucleus (core) of an atom. Atoms are tiny building blocks of matter much too small to see. An atomic bomb works by fissioning (splitting) the nuclei of atoms of the metals uranium or plutonium. It is sometimes called a fission weapon. A hydrogen bomb works by fusing (joining together) the nuclei of atoms of the gas hydrogen. Atomic bombs and hydrogen bombs are the two main kinds of nuclear weapons. The hydrogen bomb is far more powerful and destructive than the atomic bomb. The hydrogen bomb is like a tiny star. It works by the same process—the fusion of hydrogen atoms—that makes the Sun and other stars shine. A nuclear weapon destroys by the power and heat of its blast. The atomic bomb dropped on Japan flattened buildings within 3 miles (5 kilometers) of the blast. Heat from the bomb caused fires and burned everything near the place it exploded. People’s skin was burned as far as 11 miles (18 kilometers) from the blast site. A nuclear weapon also releases harmful radiation. People near thelast can die of radiation sickness even if the bomb doesn’t kill them. People farther from the blast may develop cancer and other illnesses from radiation months and years after the bomb explodes.

THE FUTURE OF NUCLEAR WEAPONS
No one has used a nuclear weapon in war since the United States dropped atomic bombs on Japan in 1945. For some years, countries tested their bombs underground or in remote places. However, test-ban treaties have halted the testing of nuclear weapons. The Cold War ended in the 1990s. It left the United States and Soviet Union with huge numbers of nuclear weapons.Other countries also have built nuclear weapons. The large number of nuclear weapons has produced new fears. What if a terrorist or an unstable government gets hold of a nuclear weapon? This possibility continues to frighten people.

Christopher Columbus


Christopher Columbus tried to take a shortcut, and ended up somewhere he never intended to go. He discovered two continents that people in Europe didn’t even know existed. By crossing the Atlantic Ocean in 1492, Columbus opened contacts between lands and peoples that were unknown to each other.
Columbus’s voyage to the Americas opened an exciting period in history. Animals, plants, and new ideas were exchanged between continents. But it also caused terrible tragedy. Millions of Native Americans died as Europeans rushed to take land and riches for themselves.

MASTER SAILOR
Christopher Columbus was born in 1451 in Genoa, Italy. He became a sailor at the age of 14. In 1476, he was shipwrecked off the coast of Portugal. Portugal was Europe’s top seafaring nation at
that time. Columbus settled there. Columbus studied geography and navigation, the science of
figuring out where things are on Earth’s surface. He became a master sailor. He met explorers who had sailed along the coast of Africa seeking an eastward sea route to the rich lands of Asia.
Europeans called these lands “the Indies.” Europeans wanted to bring gold and other treasures from the Indies back to Europe.

DARING DREAM
Columbus began to think about a wonderful adventure, which he called the “Enterprise of the Indies.” He dreamed of reaching the Indies by sailing west! This was not a new idea, but no one had ever managed to make the voyage. Columbus thought the trip to the Indies west across the ocean would be much shorter than sailing around Africa.

Columbus had high hopes, but no money. Who would pay for his expedition? He asked the king of Portugal, but the king refused. Columbus didn’t give up. He went to the rulers of Portugal’s neighbor, Spain. At first they also refused. Eventually, however, the Spanish king and queen agreed to provide three small ships—the Pinta, the Niña, and the Santa María. They also paid for crews and supplies for the voyage.

HISTORIC VOYAGE
Columbus sailed from Palos, Spain, on August 3, 1492. He stopped at the Canary Islands southwest of Spain, then headed west into unknown seas. He had no idea what lay ahead, but he had faith in his sailing skills and his bold idea. A swift current carried his ships along, and on October 12, the crew sighted the islands of the Bahamas. Columbus thought he had reached Asia. He called the islands the Indies.

Columbus was greeted by the Arawak people who lived on the islands. They offered food, but had only a little gold. Columbus was disappointed not to find Asian treasures, but still felt sure he had reached Japan in Asia. He spent two months exploring, then headed home. One of his ships sank in a storm, but back in Spain he was hailed as a hero. The king and queen offered rich rewards and made him “Admiral of the Ocean Seas.”

THREE FAILURES
Columbus made three more voyages to America. None went well. He was a skillful sailor, but his greed and stubbornness made him a bad leader and created enemies. During his second voyage (1493-1496), Columbus claimed land for Spanish settlements. He fought against Caribbean peoples who lived on the land he claimed and forced them to work as slaves. On the third voyage (1498-1500), Columbus quarreled with Spanish settlers so violently that he was sent back to Europe as a prisoner in chains. On his fourth and final voyage (1502-1504), Columbus was marooned on an island for more than a year. He had to be rescued. He was very ill by the time he returned home to Spain.

AN EXTRAORDINARY EXPLORER
Columbus died in 1506. He quarreled with the king and queen right up until his death. He wanted authority over Spanish colonies and a larger share of the riches that were brought back from America. It was a sad end to an extraordinary career that still shapes our lives today. When Columbus crossed the Atlantic, he changed the world forever.

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