KHOWLEDGE ZONE

It changed the world so much that people called it a revolution. The Industrial Revolution forever transformed the way people live and work in most parts of the world.

WHAT WAS THE INDUSTRIAL REVOLUTION?

The Industrial Revolution began when power-driven machines started doing work that people had always done by hand. It started more than 250 years ago, in about 1750. The Industrial Revolution is still going on today in some parts of the world.

Before the Industrial Revolution, most people lived by farming. There was little industry. Any manufacturing was done in homes or in small workshops close to home. People used craft skills, such as weaving or woodworking, to produce goods for their families or to sell in towns.

The Industrial Revolution took production out of homes and workshops and into big factories, where machines did much of the work. People moved from the countryside into industrial cities, where they could work in the factories. New roads, canals, railroads, and steamships were built to carry factory-made goods and the raw materials to make them.

BRITAIN LEADS THE WAY

The Industrial Revolution began in Britain. The British government was eager to increase the country's income from trade, and it encouraged industry. Business people also hoped to make more money. They saw opportunities to profit from new inventions and new ways of making goods.

British businesses began to experiment with power-driven machines. They learned that machines could make some kinds of goods more quickly, cheaply, and reliably than could craft workers. Workers were still needed to operate the machines, but not to produce goods directly.

THE AGE OF MACHINES

Waterpower provided the energy to run the first industrial machines. People built giant waterwheels that turned in currents of water. The wheels powered simple devices, such saws and millstones for grinding wheat and corn.

Advances in metalworking allowed the invention of powerful new machines, such as steam engines. By 1850, most British industry relied on coal-burning steam engines for power. In the late 1800s and early 1900s, oil-powered engines replaced steam engines.

THE RISE OF THE TEXTILE INDUSTRY

The first big factories in Britain grew up around the textile industry. For centuries, spinning yarn and weaving cloth was done mostly by hand. It was slow, patient work.

British business owners realized they could profit more by increasing production. They developed new machines that could weave cloth, and they built large, new factories to hold them. Before long, Britain was supplying cloth to countries throughout the world.

WHERE DID BRITISH INDUSTRY DEVELOP?

Huge factories were built near sources of iron, coal, and water. Three regions of Britain—northern England, central England, and central Scotland—became industrial zones. Workers moved to big new industrial cities such as Birmingham, Manchester, Newcastle on Tyne, and Glasgow.

The cities were grim places to live. Streets were dark and narrow, with rows of homes crowded side by side. Families had little space, comfort, or privacy. Homes were poorly built, without backyards, heating, or clean water. Smoke from the factories polluted city air. Factory waste and rotting trash littered the streets. Diseases such as cholera and typhoid killed thousands of people.

WORKING IN THE FACTORIES

The factories were busy, noisy, and very dangerous. Most factory workers toiled six days a week, for 12 to 15 hours every day. The pay was low. Terrible accidents were common. Many injuries occurred when workers got their hands, feet, or hair trapped in fast-moving machines.

Factory owners often recruited women and children as young as five years old to tend the machines. They could be hired for very low wages.

Some workers joined trade unions. These worker-run organizations called for better wages and working conditions. They held protest marches, went on strike, and helped workers who became injured or ill. Employers distrusted the unions and tried to crush them.

THE INDUSTRIAL REVOLUTION SPREADS

By about 1800, the new inventions and work techniques in Britain spread to Europe and North America. They were especially important in the United States. It had well-educated workers and millions of customers for factory-made goods. American companies soon built the world’s largest railroad system to transport goods and raw materials.

A second phase of the Industrial Revolution began about 1850. Inventors discovered new processes, such as better ways to make steel. In 1903, Henry Ford, an American carmaker, set up the world’s first moving assembly line. Each worker performed just one task all day long, rather than building an entire automobile.

During the 1900s, the Industrial Revolution spread to Russia, Southeast Asia, and China. Businesses there used experience gained in Europe and America to build large, productive factories.

THE INDUSTRIAL REVOLUTION TODAY

Today, there are still places in Africa, Central Asia, and South America, where the Industrial Revolution is just beginning. But in most countries, the Industrial Revolution has dramatically changed people’s lives. People who once lived in the countryside have moved to cities to find work.

As in Britain long ago, the Industrial Revolution still brings hardship to many people. It has ended traditional ways of making a living and hurt rural communities. The new roads, mines, factories, and industrial farming methods have damaged the environment.

Yet, in spite of the disadvantages, few people today want to return to the past. They believe industrialization leads to wider choices and growing wealth.

Have you ever stopped at a railroad crossing when a freight train rumbled by? Did you try to count the cars? Have you ever seen a high-speed passenger train whiz past? Trains are very important to transportation. Trains carry freight and people in places all over the world.

A train is made up of railroad cars hooked together and pulled by a locomotive. Locomotives are sometimes called engines. All trains run on tracks. Freight trains haul goods. Passenger trains carry people.

WHAT MOVES A TRAIN?

Locomotives push or pull railroad cars. They have powerful motors. The motors turn locomotive wheels that run on railroad tracks. Sometimes you will see three or four locomotives hooked together to pull a long freight train up a steep mountain.

Some locomotives get their power from electricity. The electricity comes from wires above the track or from a special third rail next to the track. Other locomotives get their power from diesel fuel, which is similar to the gasoline that most cars use. The kind of locomotive engines most used today are diesel-electrics. Engines that burn diesel fuel drive generators that make electricity. Powerful electric motors turn the wheels of a diesel-electric locomotive.

KINDS OF FREIGHT CARS

A freight train can have as many as 200 cars hooked together. There are special railroad cars for different kinds of freight.

The boxcar has four sides, a floor, and a roof. It looks like a box on wheels. Boxcars carry freight that has to be kept clean and dry, such as radios, television sets, and boxes of cereal.

Refrigerator cars work like your home refrigerator. They are boxcars that are cool inside. Refrigerator cars carry meat, fruit, frozen dinners, and other food that must be kept cold.

The hopper car is open on the top. Hopper cars carry coal, sand, gravel, and ore (rocks that contain metals). Hopper cars are easy to unload because they have doors on the bottom. The doors open and the coal, sand, or gravel pours out.

A flatcar has no top or sides. It has a floor on wheels. Flat cars carry lumber, steel beams, huge pieces of machinery, and other big items. Lifting machines called cranes load cargo onto flat cars. Special flatcars carry cars, boats, and trucks.

A tank car carries liquids or gases in a big, round tank that is lying on its side. Tank cars can carry milk, gasoline, or oil. Some tank cars carry dangerous chemicals.

KINDS OF PASSENGER CARS

Passenger cars have seats in rows along each side. Passengers can place small bags in a rack above the seat. Some passenger cars are made for long trips. They have seats that can be made into beds at night. Trains that carry passengers over long distances have special baggage cars to carry suitcases. They have dining cars where people can sit down and eat.

HOW DO TRAINS STAY ON THE TRACKS?

The track has two long rails made of steel. Pieces of wood or concrete called ties hold the rails in place and keep them from moving. Spikes hold the ties to the rails.

Locomotives, freight cars, and passenger cars have wheels that hold the train on the track. The wheels have a flange, a special shape that fits over the rails and keeps the train from slipping off the rails.

Railroad tracks are laid on a roadbed made of tightly packed dirt, gravel, or other material. When tracks have to go over rivers, the railroad company builds bridges. Sometimes railroad companies dig tunnels through mountains.

WHAT WERE EARLY TRAINS LIKE?

The first trains were wagons hooked together and pulled by horses, oxen, or other animals. The wagon wheels rolled over two strips made of wooden planks. Trains with wooden tracks were used as early as the 1500s to haul coal and stone. In the 1760s, iron rails replaced wooden ones.

Inventors made the first locomotives in the early 1800s. Early locomotive engines burned coal to heat water and make steam. The steam drove big pistons that turned the wheels. Inventors made bigger and better steam-engine locomotives. Steam engines drove most locomotives until the 1940s.

The first passenger cars were stagecoaches set on four railroad wheels. Then came larger cars with six wheels. In 1830, the Baltimore & Ohio became the first railroad in the United States to offer passenger service. The train was pulled by horses.

Passenger trains got better and better. In the late 1800s, a U.S. company called the Pullman Palace Car Company began making a comfortable sleeping car. Other companies made luxurious parlor cars for passengers to sit in. Train travel became very popular.

HOW HAS TRAIN TRAVEL CHANGED?

Many people traveled by train until the 1950s. Jet planes then began to replace trains as the most popular form of passenger travel. Today, most passenger trains in the United States and Canada are commuter trains. Passengers ride commuter trains twice a day between homes in the suburbs and jobs in the city. Trains continue to carry passengers between cities in Europe and in other parts of the world.

Some countries have high-speed trains. The first high-speed trains were in France and Japan. These trains can go about 260 kilometers per hour (160 miles per hour).

Engineers are working on a train that floats above its track. This type of train is called a maglev. Powerful magnets push the train a short distance above the rails as it moves along. Engineers are designing maglev trains that can travel much faster than trains on rails can.

You probably have a favorite television show. Maybe you have more than one favorite TV show. Did you ever wonder where your favorite shows come from? Did you ever wonder how they get to the TV set in your home?

WHERE DO TV SHOWS COME FROM?

Some TV shows are made in TV studios. Some of these shows are broadcast live—that is, as they are being made. Some shows are taped in the studio. The tape gets played on TV later on.

Other TV shows are made outside of studios. Baseball and football games and other sports events come from stadiums. Some parts of news programs are broadcast “on the scene.” TV reporters go to the scenes of accidents, floods, and fires and describe what is happening.

Shows in studios are made on sets. Sets for plays or soap operas can look like living rooms or kitchens. Sets for talk shows might have a desk for the host and chairs for the guests. Bright lights shine down on the sets.

HOW ARE TV PICTURES MADE?

A TV picture starts with a TV camera. Some TV cameras are big and some are small. The cameras in TV studios are big. Camera operators roll the big cameras around on wheels. There are usually several big cameras in a TV studio. Cameras used outside a TV studio are smaller. TV camera crews take the smaller cameras to news and sports events.

Some cameras send out live pictures to your TV set. Some cameras make videotapes that get played later on a television program.

All TV cameras need electricity to work. A camera operator points the camera at a scene. The camera picks up light from the scene. It changes this light into an electric signal called the video signal. A microphone changes the sound of people talking or music playing into an electric signal called the audio signal.

TV cameras do not snap pictures the way an ordinary camera does. Parts inside a TV camera scan, or sweep over, the scene and trace a series of thin, horizontal lines, one below the other. A TV camera scans a whole scene much faster than you can blink. Lines from the scans go together to make a picture.

THE TV CONTROL ROOM

The pictures and sound from the TV cameras and microphones go to a control room. Every television station has one or more control rooms. TV cameras in a studio can send live pictures to the control room. The control room is full of dials, switches, and small TV screens. There are screens that show pictures from each TV camera in the studio.

Producers and directors work in the control room. They make sure that the best pictures with the best views go to your TV screen at home.

People who work in control rooms also use taped pictures to make programs. They use computers to put together the best taped scenes.

HOW DOES THE SHOW GET TO YOUR HOME?

The picture and sound signals go from the control room to a transmitter. The transmitter makes the signals stronger and sends them to a transmitting antenna. This antenna is very tall. It changes the electric signals into invisible television signals that go through the air. The television signals go out from the antenna in all directions.

TV signals can get to the TV set at your home in several ways. They can go through the air to an antenna on your roof. The antenna picks up the signals and sends them through wires to your TV set. The signals could go to a cable TV company. The company sends the signals through a cable to your home. The TV signals could come right to your house from a satellite circling high above Earth. A satellite dish outside your home can pick up the TV signals and send them over wires to your TV set indoors.

HOW DOES YOUR TV SET WORK?

Your TV set changes the television signals back into pictures and sound. Your set picks up the thin lines that the TV camera scanned. Your set uses parts called electron guns to “paint” a picture on the TV screen one thin line at a time. The lines get painted from top to bottom.

A color TV set uses three electron guns to beam out three colors—red, green, and blue. These three colors make all the colors you see on your TV screen. The beams scan fast enough to paint a picture on your screen 30 times a second.

OTHER WAYS TO USE TELEVISION

Television can do many things. TV cameras can be sent to places that are difficult or dangerous for people. They can travel to outer space. Spacecraft carry TV cameras to other planets. The cameras send back pictures that let us see what other planets look like.

TV cameras on robot submarines can go deep down in the sea. Doctors use tiny TV cameras to see inside the human body.

WHEN WAS TV INVENTED?

Inventors made the first TV pictures in the 1920s. Television stations started broadcasting the first regular TV shows in the 1940s. The first TV sets had small screens. The first TV sets showed black-and-white pictures.

Television sets have gotten better and better. Most TVs sold today show color pictures. TV screens have gotten bigger and bigger. TV sets have gotten thinner. Plasma TV sets are so thin that you can hang them on a wall.

Watch a bolt of lightning flash across the sky. Flip a switch and light up your bedroom. Click the remote and see the TV come on. What do all of these things have in common? Electricity.

WHAT IS ELECTRICITY?

Electricity is a powerful force of nature. Electricity is everywhere in the universe. Electrical forces hold water, metals, and all other kinds of matter together. You can walk and run because electric signals go through your nerves from your brain to your muscles. The signals tell your muscles where to move.

Electricity makes many machines work. Electricity makes bulbs light up and runs motors in saws, fans, hairdryers, and other appliances. The computer you are using works because of electricity.

WHERE DOES ELECTRICITY COME FROM?

Electricity starts with atoms. Atoms are tiny bits of matter much too small for you to see. Everything in the universe is made up of atoms.

Atoms have two main parts: a center or nucleus, and electrons that orbit or go around the nucleus. Electricity comes from electrons. You cannot see electrons and you cannot see electricity. You can see what electricity does because of electric charge and electric energy.

WHAT IS ELECTRIC CHARGE?

Electric charge comes from the parts inside atoms. There are two kinds of electric charge called positive charge and negative charge. Positive charge comes from the nucleus of an atom. Negative charge comes from electrons. Atoms do not normally have any overall charge because their positive and negative charges cancel each other out. Charge comes when electrons move away from an atom.

Positive charge is just the opposite of negative charge. Positive and negative charges pull toward each other. The pull of positive and negative charges makes two kinds of electricity—static electricity and electric current.

WHAT IS STATIC ELECTRICITY?

Did you ever get a shock after walking across a carpet and touching a metal doorknob? That shock came from static electricity. Huge amounts of static electricity cause lightning.

Electrons that move away from their atoms cause static electricity. You can make static electricity by rubbing certain materials together. Run a plastic comb through your hair. Be sure your hair is clean and dry. Electrons jump from your hair to the comb. This gives the comb a negative electric charge. Your hair loses electrons. This gives your hair a positive electric charge. Hold the comb above your head and watch some of your hairs stand on end. Your hair stands on end because the positive and negative charges are pulling toward one another.

Static electricity also causes lightning. The pull of positive and negative charges between clouds and the ground creates a huge spark. The spark is actually the charges moving very quickly toward each other. Lightning can also be caused by opposite charges inside one cloud, between two clouds, or between clouds and the air.

WHAT MAKES LAMPS LIGHT UP?
Electric current makes lamps and all other electric devices work. Electric current is actually electrons moving in a big loop.

Something must give the electrons a push to get them moving. Batteries can start electrons flowing. Batteries are a source of electric energy. A battery, two wires, and a light bulb can make an electric circuit. The current starts flowing from the battery through a wire to the light bulb. The other wire carries the electric current back to the battery. If you cut the wire, the electric current stops. Switches on an electric circuit turn the current on and off. This is how a wall switch works to turn lights on and off in your home.

The electric energy in your home does not come from batteries. You plug appliances into electric outlets in your walls. The electric energy in the outlets comes from electric power plants.

HOW DO POWER PLANTS WORK?

Huge electric power plants generate or make electricity. Steam or falling water in dams make big machines called turbines turn. The turbine drives another machine called an electric generator. The generator makes electricity.

Long power lines carry electricity from power plants to your home. Wires inside your home bring the electric energy to light bulbs, TVs, microwaves, and your computer.

WHO DISCOVERED ELECTRICITY?

For thousands of years people knew that a material called amber mysteriously pulled on some materials. The ancient Greeks called amber elektron. Scientists in Europe in the 1600s and early 1700s called the materials that amber attracted electrics.

Benjamin Franklin, an American printer, patriot, and inventor, experimented with electricity. He thought lightning and electricity were the same thing. He did a dangerous experiment in the mid-1700s to find out. Franklin flew a kite during a thunderstorm. He attached a metal key to the kite string. An electric charge ran down the wet kite string to the key. The charge made a spark when it hit the key. This showed Franklin that lightning was electricity. He was lucky he was not killed.

Many other scientists have experimented with electricity since Benjamin Franklin. They learned how to make electricity with batteries. They found that electricity would go through wires. An American inventor named Thomas Alva Edison invented many things that use electricity, including the electric light bulb.

People in the 1800s didn’t know what to think about a new invention called the automobile. No one was sure it would catch on. In those days, people often traveled in carriages pulled by horses. So when the first automobiles appeared, people nicknamed them “horseless carriages.”

The first automobiles looked a lot like horse carriages. That was the style people knew. But the automobile soon took on a look that was all its own. The modern automobile has a hood and fenders. It has a roof, sides, and four wheels. It has seats where the driver and passengers sit. Modern automobiles are commonly called cars or autos.

Few machines are as important as cars. You can ride to school in one. Adults can drive one to work. You can drive in a car to shopping malls. You can take long vacations traveling in an automobile.

TYPES OF CARS

The typical passenger car can carry up to six people. Larger vehicles called minivans are like big cars. They can usually carry up to eight people. Pickups or trucks are built to carry cargo.

Sport-utility vehicles (SUVs) are made for driving in all types of conditions, including mud or snow. Sports cars are built for power and good road handling. Many sports cars have room for just two passengers.

Racing cars are specially designed to compete on tracks and courses. Most racing cars are built to be lightweight and very fast. Because they are made for racing, they usually are not suited for driving on public streets.

WHAT MAKES CARS GO?

A car gets power from its engine. Most auto engines burn gasoline. Gasoline goes through fuel lines from a gas tank to the engine.

When it burns fuel, the engine makes exhaust gases. These gases go out through pipes called the exhaust system.

Moving parts hooked up to the engine are called the drivetrain. The drivetrain carries mechanical energy from the engine to the wheels. The turning wheels make an automobile go.

Springs and shock absorbers give passengers a smoother ride on bumpy roads. Electrical parts make the headlights, turn signals, horn, radio, and windshield wipers work. The electrical parts also help start the car. Brake parts rub against the wheels to slow the car down. Seat belts and air bags help protect you in an accident.

HOW DO YOU DRIVE A CAR?

People don’t just jump into cars and start driving. First, they must get their learner’s permit. Local auto bureaus can tell you how. Driver-education classes teach people how to drive a car. Students learn how a car works and the rules of safe driving.

To start a car, you sit in the driver’s seat. Turning a key in the ignition starts the engine. Moving the car’s gearshift connects the engine to the drivetrain. Pressing the gas pedal on the floor sends fuel to the engine. The harder you press, the faster the car goes.

To make the car turn left or right, you turn the steering wheel in the direction you want to go. To make the car move forward or backward, you use the gearshift.

What about stopping? Press your foot down on the brake pedal. The brakes will press against the wheels, making them slow down and then stop turning.

WHEN WERE THE FIRST CARS MADE?

The first cars were built in the 1700s. They were powered by steam engines. In England, steam-powered cars weren’t allowed on the roads. They were run like trains on private railroad tracks!

Auto racing became popular in the late 1800s and early 1900s. Some early racing cars had steam engines. These included the American-made Stanley Steamer. In 1906, a Stanley Steamer hit a speed of more than 121 miles per hour (195 kilometers per hour), setting a new land speed record.

Other cars made at the time ran on electricity from batteries. People liked them because they were quiet and less likely to scare horses and people. Still other cars had gasoline engines. The first gasoline-powered cars were loud, slow, and unreliable. But over time, the cars were improved, and more people wanted to drive them.

HENRY FORD INVENTS THE ASSEMBLY LINE

In the United States, a businessman named Henry Ford started the Ford Motor Company in 1903. His company made two famous kinds of cars: the Model A and the Model T.

Ford invented the factory assembly line for making cars. Workers in one place along the assembly line worked on just one part of the car. Other workers, in another area of the assembly line, worked on another part of the car.

Automobiles made this way were not very expensive. Ordinary people could afford them. The Model T became one of the biggest-selling automobiles of all time. Henry Ford sold more than 15 million Model T cars before his company stopped making them in 1927.

MODERN CARS

Modern cars are much better than earlier models. They are easier to drive and have advanced safety features such as air bags. Engines are more efficient and powerful. Cars are quieter and more comfortable inside.

Today, cars are more popular than ever. They are the main form of transportation for many people in the United States and Canada. Many people own more than one car.

WHAT ABOUT AIR POLLUTION?

The exhaust gases that come from burning gasoline can pollute the air. These gases contain chemicals that cause a smoky pollution called smog. The worst smog forms in cities. Exhaust gases also contain a gas called carbon dioxide. Scientists think carbon dioxide pollution is making Earth’s climate warmer.

Scientists and engineers are working to reduce pollution from cars. They have made cars that burn less gasoline. They have designed exhaust systems that give off less pollution. They have also developed efficient hybrid cars.

HYBRID CARS

Many people believe hybrid cars could be a big help in reducing pollution. Hybrid cars are automobiles that run partly on gasoline and partly on some other fuel. Most hybrid cars use electricity from batteries. Scientists are also experimenting with hybrids that run on energy from sunlight and other sources.

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 the blast 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.

Can you imagine a world without cameras? There would be no photographs in newspapers, books, and magazines, or even on your computer. There would be no school pictures, no snapshots of your summer vacation, no television, and no movies.

It’s hard to imagine, but that’s what the world was like until the mid-1800s. That’s when the first cameras were made.

HOW DO CAMERAS WORK?

A basic camera works a lot like your eyes. Try this: First, close your eyes. Now quickly open and shut them. What did you see? You saw an image, or “picture,” from your surroundings.

A camera does the same thing, but it has a shutter instead of eyelids. When you take a picture, the shutter quickly opens and shuts. While the shutter is open, the camera “sees” an image, much like your eyes. The camera captures this picture.

A film camera catches the picture using chemicals on film. A digital camera captures the image electronically and stores it in memory or on a computer disk. The first popular photographs, called daguerreotypes, were captured on copper plates in the 1840s. Later, pictures were recorded on glass plates. Flexible film, much like we still use today, replaced glass plates in the late 1800s.

Like your eyes, a camera has a lens. A lens is a piece of glass shaped to focus light so the picture will be clear. Some cameras even have automatic focus, just like healthy eyes. If a camera lens is out of focus, the picture will be blurry.

HOW CAMERAS CHANGED THE WORLD

The camera changed the world. Before the camera was invented, people created pictures by painting or drawing. That took time and could be inaccurate.

Around 1840, that all changed. The camera allowed people to keep a visual record of their lives and important events. Suddenly, people could see pictures of faraway places. The camera brought the whole world into people’s homes. Photographs began to influence people’s opinions about the world.

Cameras brought big changes to family life as well. Before the camera, only wealthy people could afford to pay painters to make portraits. Suddenly, ordinary people could afford to have snapshots of themselves and their children or grandchildren.

Later, the motion-picture camera was invented. Thanks to that, we have television and movies.

CAMERAS EVERYWHERE

Today, many people have cameras. Most people use point-and-shoot cameras. A point-and-shoot camera automatically focuses the lens and controls how quickly the shutter opens and closes.

Many banks, stores, and schools use security cameras to watch what people are doing. Cameras on highways show traffic patterns. There are even tiny cameras on some computers and cell phones.

Cameras are important tools for scientists. Doctors use tiny cameras to look inside the human body. Cameras on satellites orbit Earth, taking pictures of weather patterns. Cameras bring us pictures from the deepest oceans, the insides of volcanoes, and even of distant galaxies in space! Cameras are just about everywhere.