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Old Tuesday, September 08, 2009
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Default How things work?

CAMERA

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.
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Default Airplanes

Airplanes

Airplanes are a relatively recent invention. The first one flew just over 100 years ago. As little as 50 years ago, only small numbers of people had ridden in an airplane. Today, air travel is one of the most common means of transportation.

Hundreds of thousands of people fly on airplanes each year. You buy your ticket. You pack your suitcase. Then, off you go to the airport.

The airport is where planes take off and land. An agent takes your suitcase. You go to a gate (loading and unloading area) and get on your plane. There are rows and rows of seats. You sit down next to a window. You fasten your seat belt. You are ready to take off.

PARTS OF AN AIRPLANE

The place where you sit is called the cabin. The cabin is in a long tube called the body, or fuselage, of the airplane. The front of the fuselage is called the nose. The pilot and copilot sit in the cockpit right behind the nose. The pilot steers the plane in the cockpit. Your suitcase is stowed in the cargo hold under the cabin.

Two big wings stick out from the fuselage. In back of the wings are moveable parts called flaps and ailerons. These parts help control the plane. A big tail sticks up from the end of the fuselage. A rudder, located on the back of the tail, helps the plane turn left and right.

Sets of wheels sit underneath the airplane. The airplane rolls on the wheels before it takes off and after it lands. The wheels on big planes go up into the fuselage when the plane is in the air. They come down before the plane lands.

AIRPLANE ENGINES

There are different kinds of airplane engines. Propeller engines turn propellers on the nose or on the wings. Propellers pull an airplane through the air.

Jet engines suck air in. They heat the air and shoot it out of the back of the engine. Jet engines push the plane through the air. Turboprops are a combination, using the power of a jet engine to turn a propeller.

HOW PLANES TAKE OFF

Airplanes are heavier than air. They need to go fast in order to fly. Engines and wings make a plane fly.

An airplane builds up speed on a runway. Runways at airports are long concrete strips. Runways in some faraway places can be level places made of dirt or grass. Some planes can even take off on water. When the plane is going fast enough, the pilot takes it up into the air.

FLYING A PLANE

The pilot uses many controls in the cockpit to fly a plane. The pilot pulls a wheel or stick back to make the plane go up. Air rushing over and under the wings lifts the plane into the sky.

Dials on a control panel in the cockpit tell the pilot how high the plane is, how much fuel it has, and which direction it is heading. A radar screen tells the pilot if other planes are nearby. The pilot uses the rudder on the tail and the ailerons on the wings to make the plane turn.

HOW PLANES LAND

It’s time to land. The pilot pushes the wheel or stick forward to make the plane go down. The pilot lowers the wheels and landing gear. The plane touches down on the runway. The pilot uses brakes to slow and stop the plane.

THE WORK OF AIRPLANES

Planes do different kinds of work. Passenger planes carry people in the cabin. Cargo planes carry packages, boxes, and other things. Cargo planes do not have seats.

Military cargo planes can carry soldiers, tanks, and cannons. Some military planes are fighter jets. Some are bombers. Some military jets take off and land on aircraft carriers at sea. Certain military planes can take off straight up like a helicopter, then fly ahead like a plane.

Crop-duster planes spray farm fields with chemicals that kill bugs or fertilizer that helps crops grow. Firefighting planes drop water or chemicals on forest fires. Seaplanes have skis instead of wheels. They can land on lakes in faraway places to deliver passengers, supplies, and mail.

BIG AND SMALL PLANES

The smallest airplanes are called ultralights. They weigh about 100 pounds (about 46 kilograms) and carry only a pilot. The biggest planes are jumbo jets. They can carry several hundred people and several hundred tons of cargo. Jumbo jets fly long trips over oceans.

In between, there are planes of many sizes. There are two-seater and four-seater propeller planes. There are commuter planes that can carry about 20 passengers on short trips. Airlines also fly many jets that hold from 80 to over 400 passengers.

THE FIRST AIRPLANES

Long ago, people dreamed of flying like the birds. They tried to build machines that would fly. The first people to succeed were two American brothers, Orville and Wilbur Wright. They made a heavier-than-air machine of wood and cloth. It had an engine that turned a propeller. The brothers made their first flight near Kitty Hawk, North Carolina, on December 17, 1903.

The Wright brothers and other inventors experimented with different designs. They made better and better planes. The first warplanes flew during World War I (1914-1918). Then, pilots started taking passengers on trips. Jet engines in the 1950s made air travel faster and made passenger planes very popular. Now, millions of people travel everywhere on airplanes.

AIRPLANES OF TOMORROW

Today, there are planes that can fly as fast as the speed of sound. Inventors hope to make planes that can fly five times faster than sound. They want these planes to fly up to the edge of space. Then the planes will come back down and land. They call these planes hypersonic planes. Today, it would take you more than 12 hours to fly from Chicago, Illinois, to Tokyo, Japan. In a hypersonic plane, you could make that trip in two to three hours.
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Default Radio

RADIO

There is music in the air all around you. There are sounds of people talking in the air all around you. The sounds of music and talking are carried by radio waves. There are radio waves everywhere indoors and outdoors.

Radio waves are invisible. You cannot see or feel them. You can only hear radio waves if you turn on a radio. Radios turn radio waves into sound.

HOW DOES A RADIO WORK?

Radios need electricity in order to work. Your portable radio gets electricity from batteries. Your clock radio gets electricity from a cord that you plug into an electrical outlet in a wall.

Radios have a power switch or button that lets you turn the radio on or off. Radios have a volume control that lets you play the sounds loudly or softly. Radios also have a dial or button that lets you tune in your favorite radio stations. Each station has a special number on the dial. When you tune in a station, your radio turns radio waves from that station into sound.

Radios have a special wire called an antenna that can pick up radio waves in the air. Radios first turn the radio waves into electrical signals. Then they turn the electrical signals into the sounds of music, traffic and weather reports, or news about your hometown sports teams.

HOW DO RADIO WAVES GET INTO THE AIR?

A radio station sends electrical signals through wires to a tall tower called a broadcast antenna. Electrical signals get changed into radio waves at the antenna. The antenna sends the radio waves out in all directions.

Some radio stations broadcast on AM radio waves. Some programs are broadcast on FM waves. AM radio waves travel farther than FM waves, but FM waves make clearer sounds. Most radios can pick up both AM and FM radio waves.

TWO-WAY RADIO

Radio broadcasts only go one way, from the station to your radio. You can listen to radio, but you cannot talk back. Two-way radio lets people talk to each other on radio waves.

Police officers and firefighters use two-way radio. Firefighters at a big blaze can call for more help on their two-way radios. Soldiers use two-way radios on battlefields.

CELL PHONES AND WIRELESS COMPUTERS

Cell phones use radio waves. Your cell phone sends your phone calls on radio waves to an antenna. The antenna passes your call along. You can talk on a cell phone in a car, on a bus, or just when you are walking around.

Some computers hook up to the Internet with radio waves. These computers have special antennas that can find wireless “hot spots.” These computers do not need to be plugged into a telephone line to surf the Internet.

OTHER WAYS WE USE RADIO WAVES

The radar that lets airplanes and ships “see” things in fog or things far away uses radio waves. Radar systems send out radio waves. The radio waves bounce back from any large object they hit and make images on a radar screen.

Radio waves help us explore deep space. Radio telescopes listen for radio waves from far away in the universe. Astronauts in spacecraft talk to control centers on Earth using radio waves. Radio waves beam pictures to Earth from cameras on space probes visiting other planets.

Doctors use radio waves to see inside the body. They use radio waves from MRI machines to make pictures of people’s insides.

WHO INVENTED RADIO?

During the 1800s, several scientists made discoveries that led to the invention of radio. An Italian inventor named Guglielmo Marconi sent the first sounds on radio waves in 1895. The sounds he sent were just clicks. The clicks were a kind of code that carried telegraph messages. People already knew how to send telegraph messages over wires on land. Telegraph messages sent on radio waves helped ships at sea where there were no wires. Sinking ships could send messages calling for help.

Other inventors learned how to send music and voices over radio waves. Radio stations began broadcasting programs in the 1920s. Families used to gather around the radio to listen to band music, soap operas, or other radio programs.

Inventors have found more and more uses for radio waves. Radio waves have become very important for helping you stay in touch with family and friends.
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Default Automobiles

Automobiles

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.
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Default Helicopters

Helicopters

Helicopters can fly straight up. They can fly forward, sideways, and backward. They can even hover in one place. An airplane must speed down a long runway to take off and land. Wings hold an airplane in the air. Helicopters do not need runways, and they do not have wings.

WHAT HOLDS A HELICOPTER IN THE AIR?

Big blades on top of a helicopter keep it in the air. The blades are a little like fan blades. The blades spin very fast. Wind blowing down from the whirling blades holds a helicopter up. The blades also control the direction in which the helicopter flies.

The blades make a loud chop-chop-chop noise as they turn. The noise caused people to nickname helicopters “choppers.”

Helicopters cannot fly as fast as an airplane. The fastest helicopters go about 200 miles per hour (320 kilometers per hour). They also cannot go as far as an airplane. Helicopters burn a lot of fuel.

HOW MANY BLADES DO HELICOPTERS HAVE?

The blades of a helicopter are called the rotor. Some rotors have two blades. Some rotors have three or four blades. Some big helicopters have rotors with eight blades. Big helicopters sometimes have two rotors on top.

A long metal tail sticks out from the back of most helicopters. These helicopters have a small rotor on the tail. The tail rotor blows air sideways instead of down. It helps the helicopter steer.

HOW DO YOU FLY A HELICOPTER?

A helicopter has a cockpit just like an airplane. The controls are in the cockpit. A helicopter has two control sticks, or levers. It has two pedals on the floor.

When you’re flying a helicopter, you push or pull on the stick on your left side to make the blades tilt. Tilting the blades makes the helicopter go up or down. A grip on this stick controls the speed. You twist the grip to make the helicopter go faster or slower.

The other lever is between your knees. You move this stick around to make the helicopter fly forward, backward, or sideways.

The pedals on the floor control the tail rotor. You step on the pedals to turn the helicopter. Pushing the left pedal makes the helicopter turn left. Pushing the right pedal makes the helicopter turn right.

HOW DO WE USE HELICOPTERS?

Helicopters can go places that are hard to reach. They can go places where airplanes cannot land, or where there are no roads for cars or trucks.

Helicopters can rush injured people from a car accident to a hospital. They can rescue people from the tops of burning buildings. They can pluck them from trees in the middle of raging floods. They can lift people from the decks of sinking ships at sea.

Military helicopters are important in war. They carry troops to battle. They carry wounded soldiers to hospitals. They can even shoot missiles.

Helicopters do other kinds of work. Reporters can fly in helicopters to cover news stories. Police use helicopters to chase suspected criminals. Farmers can use helicopters to spray their fields. Sometimes helicopters work on construction. The carry heavy parts to the tops of buildings.

WHO INVENTED THE HELICOPTER?

People imagined machines like helicopters hundreds of years ago. The ancient Chinese made a spinning top that could rise up into the air. The Italian artist and inventor Leonardo da Vinci drew a design for a machine like a helicopter in 1480.

The first helicopters flew in France in 1907. They were hard to control. People kept trying to build better helicopters. Finally, a Russian-born American engineer named Igor Sikorsky made a workable helicopter. It was the first helicopter with a tail rotor. He flew this helicopter in 1939. Most helicopters today are like the helicopter that Sikorsky built. Inventors and engineers are still working to make bigger and better helicopters.
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Default Telephone

TELEPHONE

What if you want to talk right now to a friend who lives far away? The answer is simple. You pick up your telephone and press some buttons. Next, you hear a ringing sound—one, two, three rings. Then you hear your friend’s voice say, “Hello.” Making a phone call seems so easy. But did you ever think about what makes it possible?

When you pick up your phone, it instantly hooks up with a vast, worldwide telephone network. The network has millions of miles of wire. It has cables that run under the oceans. It has optical (glass) fibers as thin as a hair. It has satellites that orbit high above Earth. It has powerful computers that keep track of everything on the network, including the call to your friend. The word “hello” might have zipped through wires, shot up to a satellite, or zoomed through a cable under the sea before it got to your ear.

HOW DOES YOUR TELEPHONE WORK?

Take a close look at your telephone. It has several parts. The part that you speak into is called the transmitter. The part that you put to your ear for listening is called the receiver. The buttons you press are called the dial.

Most phones have a handset and a base. The handset contains the transmitter and receiver and sometimes the dial. We often call the entire handset the receiver, even though only the part we place to our ear receives sound. Many phones have a wire that connects the handset to the base. Wires connect the base to the telephone network.

Some phones use radio signals instead of wires to send messages. Radio signals connect the handset of a cordless phone to the base. Cordless phones let you walk around while talking, but you can’t go too far. Radio signals from a cordless phone only work over a short distance.

Radio signals from a cell phone go much farther. A cell phone does not need a base to connect to the telephone network. You can take your cell phone almost anywhere. Radio signals from a cell phone go to an antenna, a tower that picks up radio signals. The area around an antenna is called a cell. The antenna in one cell can send signals to an antenna in another cell. An antenna can also send radio signals to wires in the telephone network, enabling you to call anyone you want.

HOW DOES YOUR VOICE TRAVEL?

Your voice does not really go through the telephone wires. Instead, a copy of your voice goes to the telephone network. The copy can travel through wires. It can also go through the air as a radio signal.

The telephone’s transmitter makes the copy of your voice. When you say “hello,” sound waves go into the transmitter. The sound waves hit a thin sheet of metal or plastic inside the transmitter. The sound waves make the sheet vibrate. Some vibrations are big and some are small. The transmitter turns the vibrations into electric signals. These signals are a copy of your voice saying “hello.”

The copy of your voice goes through the telephone network and into the receiver in your friend’s telephone. The way the receiver works is the opposite of the way the transmitter works. The receiver turns the electric signals into sound waves. Your friend hears the copy of your voice say “hello.” It sounds just like you!

HOW DOES YOUR FRIEND GET THE CALL?

Millions and millions of phones are connected to the telephone network. Computers and other equipment in the network can tell which phone belongs to your friend by the telephone number you dial. A telephone number is a kind of code. All phones in the United States have a code that is ten numbers long. The numbers are also called digits.

The first three digits of a phone number are called the area code. An area code tells the network what part of a state or city the phone is in. The next three digits are the exchange. They tell what neighborhood or other small area the phone is in. The last four digits tell the network exactly which phone in that area and exchange belongs to your friend.

Phone numbers in other countries have different numbers of digits. You also have to use extra numbers, called a country code, to call a different country.

BEFORE THE TELEPHONE

Before the telephone, it was hard for people to communicate over long distances. They wrote letters to each other. It could take days or even weeks for letters to be delivered.

Then people learned how to send telegraph messages. The messages traveled as electric signals that represented a code of dots and dashes. An operator on the other end converted the dots and dashes into a regular message. As the telephone became more and more popular, it largely replaced the telegraph.

WHAT CAN A TELEPHONE NETWORK DO?

Today our huge telephone network does many things besides carrying telephone calls. It sends copies of letters and pictures from one machine to another, called a fax machine. It connects computers all over the world into another vast network called the Internet. This network lets you send e-mail messages from your computer to your friends’ computers. It is hard to imagine what life would be like without the telephone.
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Default Fax

BLUETOOTH
When you use computers, entertainment systems or telephones, the various pieces and parts of the systems make up a community of electronic devices. These devices communicate with each other using a variety of wires, cables, radio signals and infrared light beams, and an even greater variety of connectors, plugs and protocols.



There are lots of different ways that electronic devices can connect to one another. For example:

•Component cables
•Electrical wires
•Ethernet cables
•*WiFi
•Infrared signals

**The art of connecting things is becoming more and more complex every day. In this article, we will look at a method of connecting devices, called Bluetooth, that can streamline the process. A Bluetooth connection is wireless and automatic, and it has a number of interesting features that can simplify our daily lives.

**The Problem
When any two devices need to talk to each other, they have to agree on a number of points before the conversation can begin. The first point of agreement is physical: Will they talk over wires, or through some form of wireless signals? If they use wires, how many are required -- one, two, eight, 25? Once the physical attributes are decided, several more questions arise:



•How much data will be sent at a time? For instance, serial ports send data 1 bit at a time, whil*e parallel ports send several bits at once.

•How will they speak to each other? All of the parties in an electronic discussion need to know what the bits mean and whether the message they receive is the same message that was sent. This means developing a set of commands and responses known as a protocol.

How Bluetooth Creates a Connection
*Bluetooth takes small-area networking to the next level by removing the need for user intervention and keeping transmission power extremely low to save battery power. Picture this: You're on your Bluetooth-enabled cell phone, standing outside the door to your house. You tell the person on the other end of the line to call you back in five minutes so you can get in the house and put your stuff away. As soon as you walk in the house, the map you received on your cell phone from your car's Bluetooth-enabled GPS system is automatically sent to your Bluetooth-enabled computer, because your cell phone picked up a Bluetooth signal from your PC and automatically sent the data you designated for transfer. Five minutes later, when your friend calls you back, your Bluetooth-enabled home phone rings instead of your cell phone. The person called the same number, but your home phone picked up the Bluetooth signal from your cell phone and automatically re-routed the call because it realized you were home. And each transmission signal to and from your cell phone consumes just 1 milliwatt of power, so your cell phone charge is virtually unaffected by all of this activity.


Bluetooth is essentially a networking standard that works at two levels:

•It provides agreement at the physical level -- Bluetooth is a radio-frequency standard.

•It provides agreement at the protocol level, where products have to agree on when bits are sent, how many will be sent at a time, and how the parties in a conversation can be sure that the message received is the same as the message sent.

The big draws of Bluetooth are that it is wireless, inexpensive and automatic. There are other ways to get around using wires, including infrared communication. Infrared (IR) refers to light waves of a lower frequency than human eyes can receive and interpret. Infrared is used in most television remote control systems. Infrared communications are fairly reliable and don't cost very much to build into a device, but there are a couple of drawbacks. First, infrared is a "line of sight" technology. For example, you have to point the remote control at the television or DVD player to make things happen. The second drawback is that infrared is almost always a "one to one" technology. You can send data between your desktop computer and your laptop computer, but not your laptop computer and your PDA at the same time. (See How Remote Controls Work to learn more about infrared communication.)

These two qualities of infrared are actually advantageous in some regards. Because infrared transmitters and receivers have to be lined up with each other, interference between devices is uncommon. The one-to-one nature of infrared communications is useful in that you can make sure a message goes only to the intended recipient, even in a room full of infrared receivers.

Bluetooth is intended to get around the problems that come with infrared systems. The older Bluetooth 1.0 standard has a maximum transfer speed of 1 megabit per second (Mbps), while Bluetooth 2.0 can manage up to 3 Mbps. Bluetooth 2.0 is backward-compatible with 1.0 devices


How Bluetooth Operates
Bluetooth networking transmits data via low-power radio waves. It communicates on a frequency of 2.45 gigahertz (actually between 2.402 GHz and 2.480 GHz, to be exact). This frequency band has been set aside by international agreement for the use of industrial, scientific and medical devices (ISM).

A number of devices that you may already use take advantage of this same radio-frequency band. Baby monitors, garage-door openers and the newest generation of cordless phones all make use of frequencies in the ISM band. Making sure that Bluetooth and these other devices don't interfere with one another has been a crucial part of the design process.

One of the ways Bluetooth devices avoid interfering with other systems is by sending out very weak signals of about 1 milliwatt. By comparison, the most powerful cell phones can transmit a signal of 3 watts. The low power limits the range of a Bluetooth device to about 10 meters (32 feet), cutting the chances of interference between your computer system and your portable telephone or television. Even with the low power, Bluetooth doesn't require line of sight between communicating devices. The walls in your house won't stop a Bluetooth signal, making the standard useful for controlling several devices in different rooms.

Bluetooth can connect up to eight devices simultaneously. With all of those devices in the same 10-meter (32-foot) radius, you might think they'd interfere with one another, but it's unlikely. Bluetooth uses a technique called spread-spectrum frequency hopping that makes it rare for more than one device to be transmitting on the same frequency at the same time. In this technique, a device will use 79 individual, randomly chosen frequencies within a designated range, changing from one to another on a regular basis. In the case of Bluetooth, the transmitters change frequencies 1,600 times every second, meaning that more devices can make full use of a limited slice of the radio spectrum. Since every Bluetooth transmitter uses spread-spectrum transmitting automatically, it’s unlikely that two transmitters will be on the same frequency at the same time. This same technique minimizes the risk that portable phones or baby monitors will disrupt Bluetooth devices, since any interference on a particular frequency will last only a tiny fraction of a second.


When Bluetooth-capable devices come within range of one another, an electronic conversation takes place to determine whether they have data to share or whether one needs to control the other. The user doesn't have to press a button or give a command -- the electronic conversation happens automatically. Once the conversation has occurred, the devices -- whether they're part of a computer system or a stereo -- form a network. Bluetooth systems create a personal-area network (PAN), or piconet, that may fill a room or may encompass no more distance than that between the cell phone on a belt-clip and the headset on your head. Once a piconet is established, the members randomly hop frequencies in unison so they stay in touch with one another and avoid other piconets that may be operating in the same room. Let's check out an example of a Bluetooth-connected system.


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Default Television

Television

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.
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Default Telephone

TELEPHONE

What if you want to talk right now to a friend who lives far away? The answer is simple. You pick up your telephone and press some buttons. Next, you hear a ringing sound—one, two, three rings. Then you hear your friend’s voice say, “Hello.” Making a phone call seems so easy. But did you ever think about what makes it possible?

When you pick up your phone, it instantly hooks up with a vast, worldwide telephone network. The network has millions of miles of wire. It has cables that run under the oceans. It has optical (glass) fibers as thin as a hair. It has satellites that orbit high above Earth. It has powerful computers that keep track of everything on the network, including the call to your friend. The word “hello” might have zipped through wires, shot up to a satellite, or zoomed through a cable under the sea before it got to your ear.

HOW DOES YOUR TELEPHONE WORK?

Take a close look at your telephone. It has several parts. The part that you speak into is called the transmitter. The part that you put to your ear for listening is called the receiver. The buttons you press are called the dial.

Most phones have a handset and a base. The handset contains the transmitter and receiver and sometimes the dial. We often call the entire handset the receiver, even though only the part we place to our ear receives sound. Many phones have a wire that connects the handset to the base. Wires connect the base to the telephone network.

Some phones use radio signals instead of wires to send messages. Radio signals connect the handset of a cordless phone to the base. Cordless phones let you walk around while talking, but you can’t go too far. Radio signals from a cordless phone only work over a short distance.

Radio signals from a cell phone go much farther. A cell phone does not need a base to connect to the telephone network. You can take your cell phone almost anywhere. Radio signals from a cell phone go to an antenna, a tower that picks up radio signals. The area around an antenna is called a cell. The antenna in one cell can send signals to an antenna in another cell. An antenna can also send radio signals to wires in the telephone network, enabling you to call anyone you want.

HOW DOES YOUR VOICE TRAVEL?

Your voice does not really go through the telephone wires. Instead, a copy of your voice goes to the telephone network. The copy can travel through wires. It can also go through the air as a radio signal.

The telephone’s transmitter makes the copy of your voice. When you say “hello,” sound waves go into the transmitter. The sound waves hit a thin sheet of metal or plastic inside the transmitter. The sound waves make the sheet vibrate. Some vibrations are big and some are small. The transmitter turns the vibrations into electric signals. These signals are a copy of your voice saying “hello.”

The copy of your voice goes through the telephone network and into the receiver in your friend’s telephone. The way the receiver works is the opposite of the way the transmitter works. The receiver turns the electric signals into sound waves. Your friend hears the copy of your voice say “hello.” It sounds just like you!

HOW DOES YOUR FRIEND GET THE CALL?

Millions and millions of phones are connected to the telephone network. Computers and other equipment in the network can tell which phone belongs to your friend by the telephone number you dial. A telephone number is a kind of code. All phones in the United States have a code that is ten numbers long. The numbers are also called digits.

The first three digits of a phone number are called the area code. An area code tells the network what part of a state or city the phone is in. The next three digits are the exchange. They tell what neighborhood or other small area the phone is in. The last four digits tell the network exactly which phone in that area and exchange belongs to your friend.

Phone numbers in other countries have different numbers of digits. You also have to use extra numbers, called a country code, to call a different country.

BEFORE THE TELEPHONE

Before the telephone, it was hard for people to communicate over long distances. They wrote letters to each other. It could take days or even weeks for letters to be delivered.

Then people learned how to send telegraph messages. The messages traveled as electric signals that represented a code of dots and dashes. An operator on the other end converted the dots and dashes into a regular message. As the telephone became more and more popular, it largely replaced the telegraph.

WHAT CAN A TELEPHONE NETWORK DO?

Today our huge telephone network does many things besides carrying telephone calls. It sends copies of letters and pictures from one machine to another, called a fax machine. It connects computers all over the world into another vast network called the Internet. This network lets you send e-mail messages from your computer to your friends’ computers. It is hard to imagine what life would be like without the telephone.
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Default Telescopes

TELESCOPES

Telescopes help us see things that are far away. They make distant objects look bigger. Using telescopes, astronomers have discovered thousands of stars, planets, moons, and many other extraordinary objects, such as black holes.

The most common type of telescope is the optical telescope. This kind of telescope gathers light from distant objects.

HOW DO OPTICAL TELESCOPES WORK?

Imagine having eyes as big as your fist. You’d look funny, but more light would enter your eyes. You would be able to see better. Telescopes bring extra light to our eyes. They effectively make our eyes bigger. Distant objects appear larger when you look through a telescope, and you can see more detail.

A refracting telescope is the simplest type of optical telescope. It is made up of two lenses. These lenses are similar to the lens in a magnifying glass. A reflecting telescope has a lens and a dish-shaped mirror. The mirror collects and focuses (concentrates) light.

A telescope’s eyepiece can be replaced by a camera. Then the image from the telescope is recorded on film or as a digital image.

GIGANTIC OPTICAL TELESCOPES

The bigger a telescope’s main lens or mirror, the more light the telescope gathers. The more light the telescope gathers, the more detail it shows, and the more distant the objects that you can see through it.

Astronomers use huge telescopes housed inside buildings called observatories. These telescopes have mirrors as large as 26 feet (8 meters) across. They gather enormous amounts of light.

BIG TELESCOPE WOES

Gigantic telescope mirrors are hard to build because they bend under their own weight. When a mirror bends, it makes a blurry image. One way to keep a giant mirror from bending is to divide the mirror into smaller sections. Another way to avoid huge mirrors is to use computers to combine images from several telescopes. The Very Large Telescope in Chile, for example, has four telescopes with 26-foot (8-meter) mirrors. Together they gather the same amount of light as a telescope with a 52-foot (16-meter) mirror.

Air causes another problem for telescopes. The air low in Earth’s atmosphere swirls about. This movement bends the light coming down from space just a bit, making the images we see through telescopes appear slightly blurry. To reduce this effect, large telescopes are often built on high mountains. This puts them above much of the air in the atmosphere. Many modern telescopes also have flexible mirrors. The shape of their mirrors can be automatically adjusted hundreds of times a second to adjust for the swirling atmosphere and keep the image sharp.

TELESCOPES THAT SEE INVISIBLE RADIATION

Optical telescopes are only one type of telescope. Astronomers also use telescopes that detect other kinds of electric and magnetic rays from space, such as X rays and radio waves. Our eyes cannot see these rays. Some objects in space aren’t bright enough to be seen with visible light. We wouldn’t know they exist without telescopes that can detect other types of radiation.

A radio telescope, for example, detects radio waves given off by planets, stars, and other objects in space. It has a huge dish that collects the radio waves and focuses them on to an antenna in the center of the dish. The dish can be turned to point at any part of the sky. The antenna turns the radio waves into electrical signals that astronomers record and study.

TELESCOPES IN SPACE

Several space telescopes are in orbit around Earth, beyond the atmosphere. From there, they have a perfectly clear view into space. This means they can see much more detail on distant objects.

Some types of radiation, such as ultraviolet light, X rays, and gamma rays cannot pass through Earth’s atmosphere. Telescopes that detect these types of radiation must be launched into space.

THE FIRST TELESCOPES

We do not know exactly who invented the telescope, but we do know it was invented in Holland at the beginning of the 17th century. The first person to look into space through a telescope was the Italian scientist Galileo. He was the first to see moons orbiting Jupiter, Saturn’s rings, and mountains on the Moon.
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