My Articles for you

NEW IDEAS ABOUT ART

2011-07-23T04:01:00.000-07:00

It can be a painting in a museum or a sculpture in a park. Or maybe a movie that knocks your socks off. It can be a painted Chinese screen, an African mask, a Persian rug, or ancient Egyptian jewelry. Or a photo that captures a moment in history. It might be a construction made out of automobile parts. It’s all art.
WHAT IS ART?
We call lots of things art today. We use the term visual arts to describe the arts we can see. Painting, sculpture, and architecture have long been the major visual arts in Europe and North America. Today, we include photography, furniture, pottery, jewelry, and many other arts and crafts among the visual arts.
Sometimes we speak of the fine arts-other forms of expression that appeal to our sense of beauty and form. This broader category includes literature, music, and dance, in addition to the visual arts.
PAINTING, SCULPTURE, AND ARCHITECTURE
Painting, sculpture, and architecture have all been around for a long time. We tend to consider them the most important forms of art.
People painted and drew on the walls of caves during the Stone Age, as long as 32,000 years ago. They made pictures of animals-probably the animals they hunted for food.
Over time, artists started painting different subjects. They painted landscapes, portraits of people, religious figures, and still lifes (fruit, flowers, and other objects that don’t move).
Sculpture is as old as painting. The first sculptures we know about are small human figures. The human figure remained the most popular subject of sculpture until the 20th century. Today, sculptors are concerned more with the materials of sculpture than with subjects. They even make sculptures out of junk and other objects they find lying around.
Architecture is both an art and a science-the art and science of making buildings. Rulers and religions are responsible for putting up some of the most impressive buildings in the world. Rulers built magnificent palaces to display their wealth and power. Religions need churches, mosques, temples, and other structures as places of worship. Religious buildings also celebrate the mysteries of religion.
WHY DO WE MAKE ART?
Everybody likes to draw, swoosh paint around with their fingers or a brush, or model things out of clay. The desire to make art is universal. People make art everywhere, and they seem to have been doing it for as long as they’ve been around.
One of the main reasons for making art is pleasure. We enjoy making art and we enjoy looking at it. We find beauty in art, and that gives us pleasure. We also admire the skill and imagination that go into making art.
Art has served other purposes, too. Think about portraits-pictures of people. Before there were cameras, a portrait was how people remembered someone who wasn’t there.
Portraits of rulers made them look powerful to impress their subjects. History paintings reminded people of victories in battle and other important events. Sculptures also commemorated rulers and victories.
Before many people could read, art instructed and educated. For example, stained glass windows in churches were meant to teach people stories in the Bible. Many paintings from the past show religious scenes.
NEW IDEAS ABOUT ART
Our ideas about art changed during the 1900s. Technology expanded our notions of art. Photographs and film are new kinds of art that developed from new inventions. Today, people also create art on computers.
Artists also changed our ideas about art. In 1913, French artist Marcel Duchamp put a bicycle wheel on display in an art gallery. Nobody considered it art at the time. But Duchamp claimed it was art because he said so.
What did Duchamp mean? He meant that he had changed how we look at the bicycle wheel by putting it in a gallery. We could now see the wheel as a beautiful object, not just as a bicycle part. He turned other everyday objects into art to make people look at things differently.
Some artists decided to get rid of subject matter. They focused instead on shapes, lines, colors, and other elements of art. These artists made what we call abstract art. You can’t see objects in abstract art. But you can respond to colors and shapes. Perhaps they make you feel happy or sad.
Art museums also broadened our ideas of art. They began to display the arts that add beauty to our homes and our bodies. These so-called decorative arts include furniture, pottery, glass, fashion, and jewelry.

AT THE ART MUSEUM
Don’t try to take in too much when you visit a museum. You’ll just get tired. Find something you like to look at. Make comparisons.
Perhaps you like a particular color. Compare paintings to see how different artists have used that color. Look for that color in other kinds of art-for example, in rugs and pottery. What other colors do artists put with your color? Does your color get brighter or dimmer as a result?
Maybe you like art with animals. Pick an animal and find it in different paintings, carvings, weavings, or pots. Has the artist made you see things about the animal you’ve never noticed before?

Choosing a PET

2011-07-20T06:02:00.000-07:00

They may be cuddly, playful, and fun. They can delight us with their grace and beauty. They’re part of our families. Sometimes, they’re our best friends. It’s easy to see why people love their pets!
THE MOST POPULAR PETS
More than half of the homes in the United States have a pet. Cats and dogs are the most popular pets. One out of three households has a cat or dog. The most popular purebred dog is the Labrador retriever. However, cats outnumber dogs in American homes.
Birds rank next in popularity, but they’re far behind cats and dogs. The most popular pet bird is the parakeet. Many people keep small animals like rabbits, hamsters, and gerbils as pets. Fish also are popular. Turtles are the reptiles most often kept as pets.
PETS NEED LOVE AND CARE
We expect our pets to love us. It’s important that we give them the love and care they need in return. Dogs especially want close contact with their owners. Our pets depend on us for food, grooming, attention, affection, and medical care. Before you get a pet, it’s important to know what its needs are.
A pet is a responsibility as well as a companion. Keeping a pet means keeping a promise to love and care for it. If you can do that, you can have wonderful experiences with pets.
CHOOSING A PET
Dogs generally offer total and unquestioning love. Most dogs are loyal friends and great playmates. Dogs also require a lot of attention. They need to be walked and played with. They need to be housebroken and trained to obey. Different breeds of dogs have different personalities and requirements, so don’t choose a dog just by its looks!
Many people who don’t have enough time to give a dog the attention it needs choose a cat instead. Cats can live indoors, and they don’t need training. Cats like to play, and they make affectionate companions. They’re endlessly curious, and they entertain us with their pranks.
Pets in cages may be best for people without a lot of time or space. Rabbits, hamsters, and gerbils are active, friendly, and easy to care for. Parakeets enjoy talking and playing with mirrors and toys. They learn to perch on your finger. Watching fish in a home aquarium is also relaxing and fun. Tropical fish can be very beautiful.
PRACTICAL PETS
Pets are fun, but they also do work. Animals can be useful to have around. That’s why wild animals got tamed as pets.
Dogs, especially, can do lots of things. They can stand guard in the night. Hunters use dogs for fetching. Ranchers use them to help herd sheep or cattle. The police use dogs to sniff for bombs. Some dogs are trained to help blind people and deaf people.
Cats catch mice. The ancient Egyptians worshiped cats for keeping their fields free of pests. Pets can even be actors! Trained dogs sometimes appear in movies or television shows.
Having a pet can be good for your health. Pets offer companionship and make people feel less lonely. Petting an animal also helps people relax.
PROBLEMS WITH PETS
Pets can cause problems, too. Dogs dig in the garden. They chew up household objects and can even bite people. Cats like to scratch furniture. Both cats and dogs can make a mess on the rug. Some people have allergies to animals.
But the biggest problem is that there are more pets than there are homes for them. Cats and dogs give birth to more cats and dogs. The number of unwanted pets is enormous. That’s why it’s important to consider having your pet neutered or spayed. Otherwise, you could wind up with lots of extra animals.

What kinds of Animals are there?

2011-07-20T05:57:00.000-07:00

Animals live everywhere. They roam the land. They burrow in the ground. They swim in the sea. They fly through the air. They creep, they leap, they soar, and they dive. A very few-including corals and barnacles-stay in one place.
Animals come in all sizes. The biggest animals are whales, which can be 100 feet (30 meters) long. The smallest animals can only be seen through a microscope.
Zoologists (scientists who study animals) have found more than 2 million species (kinds) of animals. They think they have discovered only a small portion of all animals on Earth.
Several things make animals different from other living things. Unlike plants, animals cannot make their own food. Animals eat other living things-plants and other animals-to get energy. Animal bodies are made up of more than one cell, unlike bacteria and other life forms with only one cell. Cells are the building blocks of living things. Animals also have senses, such as eyes or ears, that tell them what is going on around them.
WHAT KINDS OF ANIMALS ARE THERE?
Zoologists divide animals into about 30 groups. First, they divide them by whether they have a backbone. Animals that have a backbone are called vertebrates. Animals that do not have a backbone are called invertebrates.
The biggest and best-known animals are vertebrates. Mammals, birds, reptiles, amphibians, and fish are vertebrates. You are a vertebrate. Your backbone is also called your spine. There are about 40,000 species of vertebrates.
There are far more species of invertebrates. Even though you can probably think of many vertebrates, the many kinds of invertebrates greatly outnumber vertebrates. Almost all invertebrates are small animals. Insects, spiders, mollusks, and worms are all invertebrates. The biggest invertebrate is the giant squid. It can be up to 60 feet (18 meters) long.
COLD-BLOODED AND WARM-BLOODED ANIMALS
Zoologists divide vertebrates into two types, cold-blooded and warm-blooded animals. The body of a cold-blooded animal is the same temperature as the air or water around it. A cold-blooded animal has to stay in the sun to get warm. It must find shade to cool off. Reptiles, amphibians, and fish are cold-blooded.
The body of a warm-blooded animal stays about the same temperature all the time. Warm-blooded animals use food energy to stay warm. Some warm-blooded animals can sweat to cool off. Birds and mammals are warm-blooded.
You are warm-blooded. The normal temperature of your body stays at about 98.6° Fahrenheit (37.0° Celsius). When it is hot outside, you feel hot. You might sweat or look for an air-conditioned place. But your body temperature does not change. When it is cold outside, you feel cold. You might put on a coat or go indoors. But your body temperature does not change much.
PLANT EATERS AND MEAT EATERS
All animals eat plants, other animals, or the remains of dead animals. Animals that only eat plants are called herbivores. They eat seeds, nuts, grasses, stems, or flowers. Some mammals, such as cows, are plant eaters. Some insects, such as termites, only eat plants. Bees, moths, and butterflies suck nectar from flowers.
Animals that only eat meat are called carnivores. The meat can be from other living animals or animals that have died. Many meat eaters hunt the animals that they eat. Sharks go after smaller fish. Lions and wolves hunt deer and other mammals. Owls swoop down on rabbits, squirrels, rats, and mice. Some frogs and lizards zap insects with their sticky tongues. Hyenas and vultures mainly eat animals that are already dead.
Animals that commonly eat both animals and plants are called omnivores. Bears and opossums are omnivores. Humans are omnivores. They eat fruit, vegetables, fish, chicken, and steak.
HOW ANIMALS BREATHE
All animals must breathe oxygen to stay alive. They must breathe out a waste gas called carbon dioxide.
Some animals breathe through lungs. Lungs take oxygen out of air. Cattle, dogs, cats, whales, people, and other mammals breathe through lungs. Birds and reptiles also breathe air through lungs.
Lungs cannot take air from water. Seals, whales, dolphins, and other mammals that live in water breathe through lungs. They can stay underwater a long time because they can hold their breath for a long time.
Sharks and other fish breathe through gills. Gills take oxygen out of water. Snails, slugs, clams, squids, octopuses, and other mollusks breathe through gills. Crabs, crayfishes, lobsters, and shrimp have gills. Gills cannot take oxygen out of air.
Some animals breathe through their skin. Insects have small holes in their bodies called spiracles. Air comes in through the holes. Oxygen from the air goes through tubes to all parts of an insect’s body.
Amphibians, animals that live on land and in water, can also breathe through their skin. Amphibians also may have lungs or gills or both.

Land of Extremes

2011-07-19T01:23:00.000-07:00

Imagine mountains that seem to touch the sky and long rivers that wind through rich farmland. Imagine lush tropical rain forests full of unusual animals and huge cities teeming with millions of people. Imagine all of this and you’ll have an idea of what Asia is like.
LAND OF EXTREMES
Asia is a land of extremes. It’s the biggest of the seven continents. In fact, it covers about 30 percent of all the world’s land. Asia is so big it touches Europe in the west and nearly reaches North America in the east!
In northern Asia are the vast frozen lands of Siberia. In the south are the damp tropical forests of Malaysia and Indonesia. Asia has large, crowded cities like Mumbai (Bombay), India. It has huge, empty inland deserts like the Gobi in China. Seven of the ten longest rivers in the world flow through Asia.
Asia has the world’s highest point at Mount Everest in Nepal. It has the lowest point, too. That’s near the Dead Sea, in an area of southwest Asia called the Middle East.
At any given moment there are places in Asia that are very hot and others that are very cold. There are places that are dry as a bone and others that are rainy and wet.
CRADLE OF CIVILIZATIONS
In the Middle East, archaeologists have found traces of the world’s oldest known cities. The oldest is Jericho. It’s a city in the West Bank between Israel and Jordan. Jericho dates back more than 8,000 years.
The Middle East is often called the “cradle of civilization.” It was here, in Mesopotamia (now Iraq), that people first began to settle into communities and grow grains. That was over 10,000 years ago. Both China and India are also home to other great early civilizations.
MANY RELIGIONS
Did you know the world’s five biggest religions began in Asia? The Middle East is the birthplace of Judaism, Christianity, and Islam. India is the ancient home of Hinduism and Buddhism.
All of these religions are still practiced by millions of people in Asia. Sometimes they are the source of great conflict between Asian societies.
PEOPLE AND MORE PEOPLE
Asia has lots of people. Nearly 4 billion of them! About three of every five people in the world live in the 48 countries of Asia. China and India are the two most populated countries in the world, each with over 1 billion people.
To understand everyone in Asia you would have to learn more than 1,000 languages. Can you imagine 1,000 languages? What could they all possibly sound like?
POVERTY AND WEALTH
Many of Asia’s people are very poor. But many others are very rich. In countries such as Afghanistan, India, China, and Bangladesh, millions of people live without electricity or even clean water. In places like Japan and South Korea, millions of people live in wealthy towns and cities. They create, make, and use much of the world’s new technology.
Rich and poor and old and new. That’s Asia for you: a land of extremes.

The Past and Future of Global Warming

2011-07-07T01:48:00.000-07:00

Global Warming or Climate Change, measurable increases in the average temperature of Earth’s atmosphere, oceans, and landmasses. Scientists believe Earth is currently facing a period of rapid warming brought on by rising levels of heat-trapping gases, known as greenhouse gases, in the atmosphere.

Greenhouse gases retain the radiant energy (heat) provided to Earth by the Sun in a process known as the greenhouse effect. Greenhouse gases occur naturally, and without them the planet would be too cold to sustain life as we know it. Since the beginning of the Industrial Revolution in the mid-1700s, however, human activities have added more and more of these gases into the atmosphere. For example, levels of carbon dioxide, a powerful greenhouse gas, have risen by 35 percent since 1750, largely from the burning of fossil fuels such as coal, oil, and natural gas. With more greenhouse gases in the mix, the atmosphere acts like a thickening blanket and traps more heat.

GLOBAL WARMING IN THE PAST
Earth has warmed and cooled many times since its formation about 4.6 billion years ago. Global climate changes were due to many factors, including massive volcanic eruptions, which increased carbon dioxide in the atmosphere; changes in the intensity of energy emitted by the Sun; and variations in Earth’s position relative to the Sun, both in its orbit and in the inclination of its spin axis.
Variations in Earth’s position, known as Milankovitch cycles, combine to produce cyclical changes in the global climate. These cycles are believed to be responsible for the repeated advance and retreat of glaciers and ice sheets during the Pleistocene Epoch (1.8 million to 11,500 years before present), when Earth went through fairly regular cycles of colder “glacial” periods (also known as ice ages) and warmer “interglacial” periods. Glacial periods occurred at roughly 100,000-year intervals.
An interglacial period began about 10,000 years ago, when the last ice age came to an end. Prior to that ice age, an interglacial period occurred about 125,000 years ago. During interglacial periods, greenhouse gases such as carbon dioxide and methane naturally increase in the atmosphere from increased plant and animal life. But since 1750 greenhouse gases have increased dramatically to levels not seen in hundreds of thousands of years, due to the rapid growth of the human population combined with developments in technology and agriculture. Human activities now are a powerful factor influencing Earth’s dynamic climate.
The ice of the polar regions furnishes clues to the makeup of Earth’s ancient atmosphere. Ice cores that scientists have bored from the ice sheets of Greenland and Antarctica provide natural records of both temperature and atmospheric greenhouse gases going back hundreds of thousands of years. Layers in these ice cores created by seasonal snowfall patterns allow scientists to determine the age of the ice in each core. By measuring tiny air bubbles trapped in the ice and properties of the ice itself, scientists can estimate the temperature and amount of greenhouse gases in Earth’s past atmosphere at the time each layer formed. Based on this data, scientists know that greenhouse gases have now risen to levels higher than at any time in the last 650,000 years.
Greenhouse gases are rising, and temperatures are following. Before the late 1800s, the average surface temperature of Earth was almost 15°C (59°F). Over the past 100 years, the average surface temperature has risen by about 0.7 Celsius degrees (1.3 Fahrenheit degrees), with most of the increase occurring since the 1970s. Scientists have linked even this amount of warming to numerous changes taking place around the world, including melting mountain glaciers and polar ice, rising sea level, more intense and longer droughts, more intense storms, more frequent heat waves, and changes in the life cycles of many plants and animals. Warming has been most dramatic in the Arctic, where temperatures have risen almost twice as much as the global average.
GLOBAL WARMING IN THE FUTURE
Scientists project global warming to continue at a rate that is unprecedented in hundreds of thousands or even millions of years of Earth’s history. They predict considerably more warming in the 21st century, depending on the level of future greenhouse gas emissions. For a scenario (possible situation) assuming higher emissions-in which emissions continue to increase significantly during the century-scientists project further warming of 2.4 to 6.4 Celsius degrees (4.3 to 11.5 Fahrenheit degrees) by the year 2100. For a scenario assuming lower emissions-in which emissions grow slowly, peak around the year 2050, and then fall-scientists project further warming of 1.1 to 2.9 Celsius degrees (1.9 to 5.2 Fahrenheit degrees) by the year 2100.
Melting polar ice and glaciers, as well as warming of the oceans, expands ocean volume and raises sea level, which will eventually flood some coastal regions and even entire islands. Patterns of rainfall are expected to change, with higher latitudes (closer to the poles) projected to receive more rainfall, and subtropical areas (such as the Mediterranean and southern Africa) projected to receive considerably less. Changes in temperature and precipitation patterns may damage food crops, disrupting food production in some parts of the world. Plant and animal species will shift their ranges toward the poles or to higher elevations seeking cooler temperatures, and species that cannot do so may become extinct. Increasing levels of carbon dioxide in the atmosphere also leads to increased ocean acidity, damaging ocean ecosystems.
Human beings face global warming with a huge population at risk. The potential consequences are so great that many of the world’s leading scientists-and increasingly, politicians, business leaders, and other citizens-are calling for international cooperation and immediate action to counteract the problem.

Big Bang

2011-07-07T01:40:00.000-07:00

The universe contains everything that exists: Earth, the Sun, the stars, galaxies (collections of billions of stars), and everything else in space. People have wondered how the universe got started for thousands of years. Most scientists now think they have the answer. They think the universe began about 14 billion years ago with a kind of big explosion. They call the explosion the big bang.

WHAT HAPPENED AFTER THE BIG BANG?
No one knows what caused the big bang, but scientists think they know what happened all the way back to the first seconds after the big bang.
The brand new universe was very hot and very small. It blew outwards very fast. In the first three minutes, matter started to form. Hundreds of years later, the universe looked like a big ball of fire.
You can picture the universe as something like a black balloon with white dots painted on it. The black represents space and the white dots are galaxies. Blowing air into the balloon makes it bigger. The spaces between each dot get farther apart as the balloon expands.
As it got bigger, the universe got cooler. Hydrogen gas formed. The gas broke into clumps. The clumps came together to make galaxies and stars. Other kinds of matter formed in the stars. Finally, planets like Earth formed around some stars.
IS THERE PROOF OF A BIG BANG?
The expansion of the universe is evidence for the big bang. American scientist Edwin Hubble studied light coming from galaxies far out in the universe. In 1929, he found that the galaxies were speeding away from Earth and from each other in all directions. Scientists tracked the paths of the galaxies back to their starting place. They saw that all the galaxies must have started from the same place. Packing all that matter into a small area would make a very dense, searing hot ball-the big bang.
Scientists use math to describe how the universe behaves. In the early 1900s, German American scientist Albert Einstein came up with equations that predict an expanding universe. These equations have correctly predicted the motions of stars, planets, and light.
More proof came in the 1990s from a spacecraft called the Cosmic Background Explorer (COBE). COBE saw rays coming from far off in the universe. The rays are left over from the early days of the universe. They could only have been created in a much smaller and hotter universe long ago.
WILL THE UNIVERSE KEEP EXPANDING?
Scientists are not sure what will happen to the universe. They currently think it will keep expanding forever. They even think the expansion is speeding up. But scientists are still studying this question.

Acting

2011-07-07T01:32:00.000-07:00

Acting, the representation of a character on stage, in a motion picture, or in a television production. Acting is a formalization of play. Its symbol-making process predates writing and is thought to be a universal cultural phenomenon. Most societies have designated special times and places where make-believe activities are presented before spectators. The performers who entertain the audience by transforming themselves into human, animal, or divine characters are called actors.

The impulse to act appears to be instinctive in humans. It is related to the natural development of the imagination and of social skills in children. Mimicry, disguise, imitation, fantasy, and transformation are the sources of most play activity and complex games. Learning to pretend and mastering different roles allow children to find their place in the family and among their peers.
QUALIFICATIONS AND TRAINING
Each theatrical tradition has its own rules and conventions as to what constitutes good acting. Essentially, an actor’s talents are judged by his or her ability to effectively communicate dialogue and a sense of character to the spectator. This is normally accomplished through voice, movement, and the registration of emotion. But other artistic qualities-often difficult to describe or define-such as charm, depth of feeling, originality, plausibility, and physical attractiveness also affect the audience’s judgment.

Acting is a complex art. The professional actor’s mastery of voice projection, elocution (speaking style), diction (clarity of pronunciation), gesture, stage movement, and other abilities is only the first component of the craft. Other basic skills include the memorization of lines and cueing; manipulation of masks, costumes, and stage properties; and the embodiment of character through the expression of class status, gender, age, nationality, and temperament. Learning these skills generally takes several years. For traditional forms of Asian theater, training is often arduous. Most forms of Indian dance-drama, for example, require dedicated study beginning in early childhood to master a complex, stylized system of gestures, movements, and facial expressions.

In theater productions the actor speaks and moves in the imaginary environment of the stage, and so his or her powers of pretense must be sharply focused over an extended period of time or the entire dramatic atmosphere may collapse. Achieving a believable transformation into the character and entry into the play’s circumstances requires a constant stream of inspiration from the actor’s psyche. In many cultures, this ability to awaken the creative centers of the brain and achieve vibrant expression is the foundation of great acting. Only when the performer is properly stimulated internally can the spectator also be stirred deeply and propelled into the moment-by-moment reality of the play.
The controlled production of emotions is the actor’s special creative problem. Other artists-such as painters, sculptors, composers, or novelists-are not expected to complete a new masterpiece every night, or even every year; yet the working stage actor must perform creatively on command at an announced time and place before a live audience. Or put another way, the performing artist is forced to inhabit a character even when he or she may feel no special inspiration or artistic impulse. And since theater performances are normally repeated over several evenings or months, actors, even when successful one night, must constantly replenish, or reinspire, themselves artistically. The performer’s fear of losing certain psychic and physical energies-or growing stale in a role-has been articulated since the 1st century ad. The need to overcome this obstacle differentiates actor training from all other forms of artistic study.

Stress (Psychology)

2011-07-07T01:21:00.000-07:00

Stress (psychology), an unpleasant state of emotional and physiological arousal that people experience in situations that they perceive as dangerous or threatening to their well-being. The word stress means different things to different people. Some people define stress as events or situations that cause them to feel tension, pressure, or negative emotions such as anxiety and anger. Others view stress as the response to these situations. This response includes physiological changes-such as increased heart rate and muscle tension-as well as emotional and behavioral changes. However, most psychologists regard stress as a process involving a person’s interpretation and response to a threatening event.

Stress is a common experience. We may feel stress when we are very busy, have important deadlines to meet, or have too little time to finish all of our tasks. Often people experience stress because of problems at work or in social relationships, such as a poor evaluation by a supervisor or an argument with a friend. Some people may be particularly vulnerable to stress in situations involving the threat of failure or personal humiliation. Others have extreme fears of objects or things associated with physical threats-such as snakes, illness, storms, or flying in an airplane-and become stressed when they encounter or think about these perceived threats. Major life events, such as the death of a loved one, can cause severe stress.
Stress can have both positive and negative effects. Stress is a normal, adaptive reaction to threat. It signals danger and prepares us to take defensive action. Fear of things that pose realistic threats motivates us to deal with them or avoid them. Stress also motivates us to achieve and fuels creativity. Although stress may hinder performance on difficult tasks, moderate stress seems to improve motivation and performance on less complex tasks. In personal relationships, stress often leads to less cooperation and more aggression.
If not managed appropriately, stress can lead to serious problems. Exposure to chronic stress can contribute to both physical illnesses, such as heart disease, and mental illnesses, such as anxiety disorders. The field of health psychology focuses in part on how stress affects bodily functioning and on how people can use stress management techniques to prevent or minimize disease.

Eclipses

2011-07-02T06:45:00.000-07:00

Because of the tilt of the Moon’s orbit, the Moon usually passes above or below the Sun at new moon and above or below Earth’s shadow at full moon. Sometimes, though, the full moon or new moon crosses the plane of Earth’s orbit. By a coincidence of nature, even though the Moon is about 400 times smaller than the Sun, it is also about 400 times closer to Earth than the Sun is, so the Moon and Sun look almost exactly the same size from Earth. If the Moon lines up with the Sun and Earth at new moon (when the Moon is between Earth and the Sun), it blocks the Sun’s light from Earth, creating a solar eclipse. If the Moon lines up with Earth and the Sun at the full moon (when Earth is between the Moon and the Sun), Earth’s shadow covers the Moon, making a lunar eclipse.

A total solar eclipse is visible from only a small region of Earth. During a solar eclipse, the complete shadow of the Moon that falls on Earth is only about 160 km (about 100 mi) wide. As Earth, the Sun, and the Moon move, however, the Moon’s shadow sweeps out a path up to 16,000 km (10,000 mi) long. The total eclipse can only be seen from within this path. A total solar eclipse occurs about every 18 months. Off to the sides of the path of a total eclipse, a partial eclipse, in which the Sun is only partly covered, is visible. Partial eclipses are much less dramatic than total eclipses. The Moon’s orbit around Earth is slightly elliptical, or egg-shaped. The distance between Earth and the Moon varies slightly as the Moon orbits Earth. When the Moon is farther from Earth than usual, it appears smaller and may not cover the entire Sun during an eclipse. A ring, or annulus, of sunlight remains visible, making an annular eclipse. An annular solar eclipse also occurs about every 18 months. Additional partial solar eclipses are also visible from Earth in between.

At a lunar eclipse, the Moon is actually in Earth’s shadow. When the Moon is completely in the shadow, the total lunar eclipse is visible from everywhere on the half of Earth from which the Moon is visible at that time. As a result, more people see total lunar eclipses than see total solar eclipses.

Relativity

2011-07-02T06:39:00.000-07:00

Relativity, theory, developed in the early 20th century, which originally attempted to account for certain anomalies in the concept of relative motion, but which in its ramifications has developed into one of the most important basic concepts in physical science. The theory of relativity, developed primarily by German American physicist Albert Einstein, is the basis for later demonstration by physicists of the essential unity of matter and energy, of space and time, and of the forces of gravity and acceleration.
GENERAL THEORY OF RELATIVITY
In 1915 Einstein developed the general theory of relativity in which he considered objects accelerated with respect to one another. He developed this theory to explain apparent conflicts between the laws of relativity and the law of gravity. To resolve these conflicts he developed an entirely new approach to the concept of gravity, based on the principle of equivalence.
The principle of equivalence holds that forces produced by gravity are in every way equivalent to forces produced by acceleration, so that it is theoretically impossible to distinguish between gravitational and accelerational forces by experiment. In the theory of special relativity, Einstein had stated that a person in a closed car rolling on an absolutely smooth railroad track could not determine by any conceivable experiment whether he was at rest or in uniform motion. In general relativity he stated that if the car were speeded up or slowed down or driven around a curve, the occupant could not tell whether the forces so produced were due to gravitation or whether they were acceleration forces brought into play by pressure on the accelerator or on the brake or by turning the car sharply to the right or left.

Acceleration is defined as the rate of change of velocity. Consider an astronaut standing in a stationary rocket. Because of gravity his or her feet are pressed against the floor of the rocket with a force equal to the person’s weight, w. If the same rocket is in outer space, far from any other object and not influenced by gravity, the astronaut is again being pressed against the floor if the rocket is accelerating, and if the acceleration is 9.8 m/sec2 (32 ft/sec2) (the acceleration of gravity at the surface of the earth), the force with which the astronaut is pressed against the floor is again equal to w. Without looking out of the window, the astronaut would have no way of telling whether the rocket was at rest on the earth or accelerating in outer space. The force due to acceleration is in no way distinguishable from the force due to gravity. According to Einstein’s theory, Newton’s law of gravitation is an unnecessary hypothesis; Einstein attributes all forces, both gravitational and those associated with acceleration, to the effects of acceleration. Thus, when the rocket is standing still on the surface of the earth, it is attracted toward the center of the earth. Einstein states that this phenomenon of attraction is attributable to an acceleration of the rocket. In three-dimensional space, the rocket is stationary and therefore is not accelerated; but in four-dimensional space-time, the rocket is in motion along its world line. According to Einstein, the world line is curved, because of the curvature of the continuum in the neighborhood of the earth.
Thus, Newton’s hypothesis that every object attracts every other object in direct proportion to its mass is replaced by the relativistic hypothesis that the continuum is curved in the neighborhood of massive objects. Einstein’s law of gravity states simply that the world line of every object is a geodesic in the continuum. A geodesic is the shortest distance between two points, but in curved space it is not generally a straight line. In the same way, geodesics on the surface of the earth are great circles, which are not straight lines on any ordinary map.

Elephant Quick Facts

2011-06-22T12:27:00.000-07:00

Class-Mammalia
Order-Proboscidea
Family-Elephantidae
Genus/Species-Elephas maximus (Asian)
Loxodonta africana (African)
Loxodonta cyclotis (African)
Names- male: bull
female: cow
young: calf
group: herd
Conservation Concerns-Endangered due to illegal hunting and habitat destruction.
Range-Asian elephants inhabit small areas of India, Sri Lanka, China, and Southeast Asia.
African elephants are found in Africa south of the Sahara.
Habitat-Forests, savannas, river valleys, and marshes.
Size-Asian elephants weigh up to 5000 kg (11,000 lb) and stand about 3 m (10 ft) tall.
African elephants weigh up to 7000 kg (15,400 lb) and stand up to 4 m (13 ft) tall.
Females are typically smaller than males.
Feeding Habits-Elephants are herbivores; they eat grasses, bark, roots, leaves, and fruit. They consume from 200 to 300 kg (440 to 660 lb) of food, and up to 150 liters (40 gallons) of water daily.
Offspring-Female elephants usually give birth to one calf after a gestation period of 20 to 22 months.
Life Span-About 60 years.
Did You Know-The two fingerlike projections at the tip of the elephant’s trunk are facile enough to pick a blade of grass.
Although an elephant’s skin is 2-4 cm (0.8-1.6 in) thick, it is very sensitive.
Elephants communicate in frequencies below human perception.
Tusks are actually an elephant’s second set of upper incisor teeth, and continue to grow throughout the elephant’s life.
An elephant’s ears help it stay cool; as it flaps its ears, heat dissipates through abundant blood vessels.

Hypertext Markup Language (Html)

2011-06-22T12:25:00.000-07:00

Hypertext Markup Language (HTML) in computer science, the standard text-formatting language since 1989 for documents on the interconnected computing network known as the World Wide Web. HTML documents are text files that contain two parts: content that is meant to be rendered on a computer screen; and markup or tags, encoded information that directs the text format on the screen and is generally hidden from the user. HTML is a subset of a broader language called Standard Generalized Markup Language (SGML), which is a system for encoding and formatting documents, whether for output to a computer screen or to paper.

Some tags in an HTML document determine the way certain text, such as titles, will be formatted. Other tags cue the computer to respond to the user’s actions on the keyboard or mouse. For instance, the user might click on an icon (a picture that represents a specific command), and that action might call another piece of software to display a graphic, play a recording, or run a short movie. Another important tag is a link, which may contain the Uniform Resource Locator (URL) of another document. The URL can be compared to an address where a particular document resides.The document may be stored on the same computer as the parent document or on any computer connected to the World Wide Web. The user can navigate from document to document simply by clicking on these links. HTML also includes markups for forms, that let the user fill out information and electronically send, or e-mail, the data to the document author, initiate sophisticated searches of information on the Internet, or order goods and services.

The software that permits the user to navigate the World Wide Web and view HTML-encoded documents is called a browser. It interprets the HTML tags in a document and formats the content for screen display. Since HTML is an accepted standard, anyone can build a browser without concerning themselves with what form various documents will assume, unlike documents produced by typical word processors, which must be translated into a different format if another word processing application is used. Most sites on the World Wide Web adhere to HTML standards and, because HTML is easy to use, the World Wide Web has grown rapidly. HTML continues to evolve, however, so browsers must be upgraded regularly to meet the revised standards.

Architecture

2011-06-13T03:30:00.000-07:00

We ask for a lot from our buildings. They have to keep out the rain, wind, rats, and bugs, not to mention our enemies. They need to store our stuff, keep us warm when it’s cold, and keep us cool when it’s too hot. We also like our buildings to be well constructed and beautiful.

Architecture is the important art and science of making buildings. Architects are the bosses who design buildings and supervise their construction.

WHAT ARE BUILDINGS MADE OF?

Buildings once were made of whatever materials were available. Where forests grew, for example, people used wood. Where there were no trees, people used the earth itself. They dried mud in the sun to make bricks. In the far north, they used blocks of snow or ice.

These materials aren’t long-lasting, however. Mud bricks wear away. Wooden buildings catch fire and burn down.

Stone won’t catch fire, and it can be expected to endure. Many kinds of stone, including marble and limestone, are good materials to build with. Steel is strong and lightweight. It lets architects build tall buildings, like skyscrapers.
But deciding on what materials to use isn’t usually the first thing an architect thinks about. The architect needs to know the reason for the building. How will the building be used?

REASONS FOR BUILDINGS

Shelter is the most basic reason for building. Buildings shelter us at home, at work, and at play. All buildings must shelter us from rain, wind, sun, and cold.

Buildings also provide security. Some of the world’s most permanent structures were built to defend against enemies. Castles had moats and drawbridges to keep enemies out, and high walls from which to pour down boiling oil on them.

Some of the most impressive buildings provide places for worship. Temples, churches, and mosques must meet spiritual needs. The soaring heights of a Gothic cathedral, for example, inspire amazement and admiration.

Some buildings are just for showing off. Kings and emperors insisted on grand palaces and castles. People with money have always demanded that architecture display their wealth. Today, large corporations, governments, and universities demonstrate their importance by putting up impressive buildings.

Architects today design all kinds of buildings. Our way of life calls for office buildings, large apartment complexes, shopping centers, schools, hospitals, airports, and hotels.

LANDMARK ARCHITECTURE

We judge the beauty of architecture in various ways. Some buildings have been judged especially great. In the past, architects lavished attention on religious structures. Today, many of the most exciting buildings are museums and houses.

Many people think the Greek temples are the most beautiful shrines of all time. The Greeks put columns around the outside of their temples. One masterpiece is the Parthenon, a temple on a hilltop in Athens, Greece. We admire its simplicity, but the carvings on the temple were once painted bright colors.

Saint Peter’s in Vatican City was a major project of the 1500s. With its dome by Michelangelo, Saint Peter’s influenced many state capitol buildings in the United States.

America’s most famous architect is Frank Lloyd Wright. A number of his buildings are national landmarks. Most famous are the Guggenheim Museum in New York City and Fallingwater, a house in Pennsylvania. The Guggenheim’s spiraling ramp provides a dramatic showcase for artwork. Fallingwater overlooks a stream and waterfall. Its terraces appear to project from the surrounding hillside.

Frank Gehry designs buildings that combine many irregular shapes. His Guggenheim Museum in Bilbao, Spain, uses titanium metal to create a curving, lightweight surface that shimmers in sunlight.

Exercise

2011-06-13T03:23:00.000-07:00

People exercise to keep healthy. They exercise to lose weight or to stay fit. They exercise to make their muscles bigger and stronger. Maybe you play soccer or some other sport for exercise. Getting exercise can be fun and can make you feel good.

Exercise is a big part of staying physically fit. People who are physically fit are alert and full of energy. Exercise can also help people handle stress. Exercise is especially good for children, teens, and older persons.

NOT ALL EXERCISE IS THE SAME

There are two main types of exercise: aerobic and anaerobic. Aerobic exercise works big muscles in your arms and legs. Aerobic exercise makes your muscles use oxygen faster than usual. It makes your heart and lungs work harder to supply your muscles with oxygen. Running, walking, jogging, and swimming are kinds of aerobic exercise.

Anaerobic exercise works just a few muscles at a time. Weightlifting is a kind of anaerobic exercise. Weightlifting and other kinds of anaerobic exercise make your muscles bigger and stronger. Anaerobic exercise does not require a lot of oxygen. It does not work your heart or lungs. You can only do anaerobic exercise for short periods of time because the muscles you’re using quickly get tired.
EXERCISE THAT HELPS THE HEART

Doctors say that regular aerobic exercise leads to a healthier heart. Jogging, walking, riding a bicycle, and other aerobic exercises lower the risk of heart disease. In one kind of heart disease, fatty stuff called plaque builds up in blood vessels going to the heart. Aerobic exercise helps prevent this buildup. Aerobic exercise also makes the heart and lungs stronger.

Doctors say you should do 20 to 30 minutes of aerobic exercise at least three times a week. You need to exercise hard enough to get your heart beating faster than normal. You can feel your heart beating. Use two fingers to feel a beat, or pulse, in your wrist or neck.

EXERCISE THAT INCREASES STRENGTH

Some kinds of exercise are better at increasing strength than others. Usually people work out with weights if they want to improve their muscle strength. They use free weights, weights that are not attached to anything, such as barbells. Or they use strength-training machines. Strength training can also make bones stronger.

It is a good idea to have a trainer or physical education teacher show you how to lift weights properly. It is important not to injure yourself when lifting weights. Start out with small weights. Try lifting heavier and heavier weights as your muscles get stronger.

EXERCISE THAT HELPS CONTROL WEIGHT

Aerobic exercise can help you lose weight. It can help you stay at a healthy weight. Aerobic exercise burns calories.

A calorie is a unit of measurement. It measures the amount of energy in foods. It measures the amount of energy your body uses.

When you take in the same number of calories that you burn every day, your weight stays the same. If you take in more calories than you burn, you gain weight. If you take in fewer calories than you burn, you lose weight. Regular exercise helps you burn calories.

Strength training may also help with weight control. Lifting weights burns calories. Lifting weights also makes more muscle in your body. Muscles burn more calories than fat.

EXERCISE THAT MAKES YOU FLEXIBLE

Stretching exercises can make your body more flexible. There are stretches for your arms, legs, neck, and trunk. Many people do slow exercises and stretches called yoga to make their bodies more flexible. A physical education teacher can show you how to do stretches.

You should do warm-up stretches before you do aerobic or anaerobic exercises. You should do cool-down stretches when you are finished exercising. Warm-up and cool-down stretches can help prevent muscle injuries.

Medical Care

2011-06-13T03:20:00.000-07:00

Do you ever visit the doctor? Sometimes people visit doctors because they are not feeling very well. Sometimes people visit doctors for a physical examination, or checkup. Visits to doctors are part of medical care. Many other people also contribute to medical care.

WHAT DO DOCTORS DO?

Doctors try to diagnose, or figure out, what makes people sick. If you have a sore throat or a bad cough, the doctor examines you with a stethoscope. The doctor uses the stethoscope to listen to your heartbeat and to the sound your lungs make when you breathe. The doctor looks into your nose, ears, and throat and may order some laboratory tests. Then the doctor diagnoses your problem. Sometimes the doctor tells you your body will get well on its own. Sometimes the doctor orders drugs to help you.

Some doctors are specialists. They have extra training. Different kinds of specialists treat heart disease, cancer, arthritis, and other diseases. Some specialists only treat children or old people. Other specialists do surgery. Surgeons can take out diseased organs and even replace hearts, lungs, and livers. Some surgeons fix broken bones and replace knees and hips.
WHAT DO NURSES DO?

Many other people besides doctors provide medical care. Nurses, for example, are very important to medical care.

Have you had your tonsils out? Did you go to the hospital? If you did, nurses probably took care of you. Nurses care for sick patients.

Nurses help doctors do examinations and give treatments. Special nurses called nurse practitioners do many things that doctors once did. They diagnose what is causing an illness and prescribe drugs. Surgical nurses help with operations. Nurse-midwives deliver babies and care for mothers.

WHAT DO OTHER MEDICAL WORKERS DO?

If you have a sore throat, your doctor may take some mucus from the inside of your throat. Medical laboratory technicians study this material to see if there are disease-causing germs. Laboratory technicians also examine blood samples for signs of illness.

When people fall and hurt themselves, medical imaging technicians take X rays of the bones. The pictures show if any bones are broken. Other medical imaging tools can show if there are any clumps of abnormal cells called tumors inside the body.

Physician’s assistants sometimes work in places where there is no doctor nearby. They do many of the things that doctors do. They also talk to a physician by telephone or e-mail. Dentists look after your teeth. Psychologists and psychiatrists work on mental health.

Genes and Heredity

2011-06-13T03:17:00.000-07:00

Have you ever heard a news reporter talk about DNA? Reporters talk about DNA found at the scene of a crime. They talk about police finding DNA “fingerprints.” Police sometimes use DNA as a clue to find out who committed the crime.

WHAT IS DNA?

DNA is a substance that makes up genes. Everything alive has genes. Plants have genes. Animals have genes. You have genes.

Genes are the basic units of heredity. Heredity means all the characteristics you inherit from your parents. You get your genes from your parents. You inherit half of your genes from your mother. You inherit half of your genes from your father.

Genes are a kind of code. A tree’s genes tell what shape its leaves will be. A cat’s genes tell what color its fur will be. Your genes tell what color your eyes will be. Your genes tell what color your hair will be. Everything about you comes from the code in your genes.

WHERE ARE GENES?
Genes line up on strands called chromosomes in cells. Everything alive is made up of cells. Chromosomes are in the center, or nucleus, of cells.

Different parts of you are made of different kinds of cells. Your muscles are made of muscle cells. Your skin is made of skin cells. The code in your genes tells your body to make different kinds of cells. The genes in each cell tell the cell how to work. They tell the cell when to make new copies of itself.

WHO DISCOVERED GENES?

An Austrian monk named Gregor Mendel first saw inherited patterns in pea plants. He experimented with pea plants in the 1860s. One of the things, or traits, Mendel studied was what makes some pea plants tall and some short. He said that the traits must come from units of heredity passed from the parent plants. These units were later called genes.

In the mid-1900s, scientists discovered that genes are made of DNA. In the 1970s, scientists learned how to change DNA with genetic engineering. Scientists also learned that problems with certain genes cause diseases. Muscular dystrophy, cystic fibrosis, and hemophilia are some genetic diseases-diseases caused by problems in genes. Today, scientists are looking for ways to cure genetic diseases by altering genes through a process called gene therapy.

Numbers

2011-06-13T03:15:00.000-07:00

They can be positive or negative, odd or even. They can be whole or in parts. Without them you wouldn’t be able to tell the time. You wouldn’t even know how old you are. And how about this-without them you wouldn’t have any math homework!

What are they? They’re numbers. And you use them every single day.

WHAT IS A NUMBER?

A number is a word or a symbol. It usually represents an amount, such as 3 keys in your pocket or a bill worth 5 dollars. Numbers are used for all kinds of things. They’re on clocks and cash registers, on thermometers and license plates. You see them on road signs and calendars.

WHO USES NUMBERS?

Everyone uses numbers sometimes, but some people use numbers a lot. Scientists use numbers to describe the size of distant galaxies or to calculate the paths of rocket ships in space. Accountants use numbers to keep track of money. Baseball fans use numbers to measure how well players are doing. And that’s just a small sample of the ways we use numbers.
WHOLE NUMBERS

The numbers we see and use most often are called whole numbers. These are numbers such as 1, 6, or 12. But believe it or not, whole numbers are only one of several kinds of numbers.

NEGATIVE NUMBERS

A negative number is a whole number that is less than zero. Negative numbers are only used for certain kinds of measurements. You can’t hold -2 pears in your hand! But you can give 2 pears to someone else, so that you have 2 less than you did before. When it’s really cold outside, the temperature can be -6 degrees Fahrenheit. Or a running back in football might have 6 carries for -13 yards (if he’s having a bad day).

FRACTIONS

Have you ever eaten half of an apple? Then you’ve eaten a fraction of an apple. A fraction is a number that represents just a part of something, not the whole thing. Fractions are not whole numbers. That half an apple you ate can be written like this: y of an apple. The apple was divided into 2 parts and you ate 1. If you ate a quarter of a pizza, you’d be eating of it (1 part in 4). Got it? A fraction is created by dividing one whole number by another.

PRIME NUMBERS

Mathematicians are scientists who study math. For them, prime numbers are one of the most interesting types of numbers. A prime number can only be evenly divided by two whole numbers: itself and the number 1.

Take 7 for example: 1 × 7 = 7, right? But that’s the only way you can multiply two numbers get exactly 7, so 7 is a prime number. Now take 8: 1 × 8 = 8, but so does 2 × 4. So 8 is not a prime number. Prime numbers are so special that they have been used to create secret codes!

UNIVERSAL LANGUAGE

One way to think about numbers is as the universal language of science. It doesn’t matter what language you speak, numbers and math work the same way even if the symbols are different. Numbers allow scientists from different countries to share their work and to advance understanding, even if they speak completely different languages.

Gravity

2011-06-13T03:11:00.000-07:00

Try to jump as high as you can. Bend your knees. Now jump! No matter how hard you try, or how high you jump, you always come back down again.

Something called gravity pulls you back down. Gravity holds you down on Earth. Without gravity, you would fly off into space. You would jump up and just keep on going. That might sound like fun, but you could not live very high up. For one thing, you need to breathe air. The higher you go, the less air there is. You need gravity to keep you down on Earth.

WHAT IS GRAVITY?

Gravity is a force that pulls two objects toward each other. The force is also called gravitation. The bigger an object is, the stronger its gravity. Small objects, and even cars and buildings, have so little gravity that you can’t feel their pull. Huge objects like Earth, however, are a different story.
Earth is so much bigger than you that its gravity makes you “stick” to the ground. Earth is bigger than the Moon. Earth’s gravity pulls on the Moon. That is why the Moon orbits, or goes around, Earth. The Sun is bigger than Earth. Its gravity makes Earth go around the Sun.

Earth’s gravity pulls toward the center of Earth. Gravity holds the oceans and the atmosphere on Earth. The Sun’s gravity pulls toward the center of the Sun. It holds the Sun together.

WHO DISCOVERED GRAVITY?

Gravity has always been around. In ancient times, people tried to explain why things fall toward Earth. An English scientist named Sir Isaac Newton came up with a great idea about gravity in 1687. He thought about how an apple falls and wondered how far gravity went. He came up with the idea that gravity does more than hold people on Earth.

Newton thought of gravity as a kind of mysterious force pulling objects together. He said that gravity holds the Moon in orbit around Earth. It holds the planets in orbit around the Sun. Newton’s ideas on gravitation explained many things about how apples fall and how stars and planets move.

A DENT IN SPACE-TIME

In the early 1900s, another scientist named Albert Einstein came up with a very different idea of what gravity is. Einstein had some pretty amazing ideas. He said there was something called space-time. He thought of gravity as a dent in space-time.

This is not as hard to imagine as it might seem. Think about placing a bowling ball on a soft mattress. The mattress is like space-time. The bowling ball is like a star. The bowling ball makes a dent in the mattress. This is sort of how a star dents space-time. If you try to roll a tennis ball past the bowling ball, it curves around the bowling ball as it passes through the dent.

The planets in our solar system roll around the dent in space-time made by the Sun. The dent keeps planets from going off into space. The dent in space-time keeps the planets going around the Sun.

Scientists are still not sure what causes gravity. Finding out more about gravity is an important problem for the future.

Virus

2011-06-13T03:09:00.000-07:00

When you wake up with the sniffles not feeling too well, you probably have a cold. Colds are caused by viruses. Other viruses cause the flu and some very serious illnesses such as chicken pox, measles, rabies, and AIDS. Scientists think viruses might also be a cause of some cancers. Many viruses can go from one person to another.

A TINY GERM

A virus is a tiny germ that can infect the body. Different kinds of viruses can also infect animals and plants. There are thousands of kinds of viruses. There are about 100 kinds of viruses that cause colds.

Viruses are much too small for scientists to see even with an ordinary microscope. Scientists must use a powerful electron microscope to see viruses.

A virus is a pretty simple thing. It has two basic parts. It has an outer part called a protein coat. Inside the coat, it has genes. Genes are tiny structures that tell plants and animals how to grow and what shape to be.

A VIRUS ATTACKS

Each kind of virus infects, or attacks, a different type of cell. All parts of your body are made of units called cells. Cold viruses head for the lining of your nose or throat. Sometimes the cold virus spreads to the air passages that lead to your lungs.
When a cold virus gets into your nose cells, it tries to take over. First, it takes off its protein coat. Next, it lets its genes go free. The genes command your nose cells to make more of the virus. The virus actually uses part of you to make copies of itself.

WHY DO YOU FEEL SICK?

More and more viruses grow in the cells that make up the lining of your nose. They burst out of one nose cell and head for other nose cells. This is how the infection spreads.

An infected nose cell dies after the new viruses burst out. As your nose cells die, your head feels stuffy. Your nose starts to run. Dying cells make you feel sick.

HOW DO VIRUSES SPREAD?

You can give your cold virus to someone else. You send out viruses when you cough or sneeze. Another person can breathe in the virus from the air near you. The virus gets on your hands when you blow your nose. Other people can get the virus by touching what you have touched and then touching their nose, eyes, or lips. You can help keep a cold virus from spreading by covering your mouth when you cough or sneeze. You should also wash your hands often.
Different viruses spread in other ways. The rabies virus is in the saliva (spit) of an infected dog. The dog spreads the virus when it bites. Mosquito bites can also spread viruses. West Nile Virus goes from birds to mosquitoes when the mosquitoes bite the birds. The mosquitoes then spread the virus when they bite humans and other animals.

The virus that causes AIDS is in blood and other body fluids. The viruses that cause cold sores and chicken pox get in through the skin. Other viruses live in food and get into people who eat the food.

FIGHTING A VIRUS

When a cold virus attacks, your body fights back. Your body sends special white blood cells up to your nose. These cells are part of your immune system. The immune system cells kill the virus. After a few days, you get over your cold.

The immune system cannot kill every kind of virus. The viruses that cause cold sores and chicken pox hide in nerve cells. The immune system cannot find them there. Some viruses can kill people. The AIDS virus and the rabies virus are germs that can kill people.
There are no drugs that can cure a disease caused by a virus. Antibiotics do not kill viruses. Antibiotics only kill other kinds of germs called bacteria.

Scientists are trying to make drugs that will kill viruses. They have made some drugs that help control viruses. Some of these drugs help people with AIDS stay alive.

PREVENTING INFECTION

Doctors use a type of medicine called a vaccine to keep some kinds of viruses from making people sick. Vaccines often have dead or weakened viruses in them. There are vaccines for measles, chicken pox, rabies, flu, and other diseases caused by viruses.

All vaccines work pretty much the same way. You will not get measles, for example, if you get the measles vaccine. A doctor or nurse gives you a shot of the vaccine. The vaccine puts the measles virus into your body. The vaccine virus is too weak to cause measles, but your immune system does not know that. Your immune system attacks. It learns how to destroy the measles virus. If a real measles virus later gets into your body, your immune system will remember how to defeat it. It will wipe out the virus before it takes over your cells.

USING VIRUSES

Scientists are studying ways to use viruses as tools. They think of cells infected by viruses as being like little factories. They want to use viruses to force cell factories to make chemicals used in medicines.

Viruses may also be able to help treat diseases caused by missing or damaged genes in humans. Harmless viruses could carry healthy genes into cells. The healthy genes might cure the disease.

Some kinds of cancer might one day be cured by viruses. Scientists may learn how to make special killer viruses that would attack cancer cells.

Alligators and Crocodiles

2011-06-13T03:04:00.000-07:00

What is the difference between an alligator and a crocodile? That’s kind of a trick question. “Crocodile” is a common name for an order, or large group, of animals called crocodilians. Alligators, caimans, and gavials are all crocodilians-but so are crocodiles.

HOW ARE THEY DIFFERENT?

One way to tell the difference between alligators and crocodiles is by looking at their snouts. Alligators and their close relative, the caiman, have broad, rounded snouts. Crocodiles have longer, sharper snouts that are shaped like triangles.

Crocodiles have a tooth on each side of their lower jaw that sticks up when their mouth is closed. Alligators do not show any teeth when their mouths are closed.

The Indo-Pacific, or saltwater, crocodile is one of the biggest reptiles. It is about 23 feet (7 meters) long and weighs more than 2,000 pounds (more than 1,000 kilograms). The American alligator is smaller. It can grow to 20 feet (6 meters) long.
Crocodiles live in warm, tropical places. Alligators can live in cooler places as well as warm environments.

HOW ARE THEY THE SAME?

All crocodilians are reptiles. They are cold-blooded. This means they must warm up by lying in the sun. They cool off by staying in the shade.

Crocodilians breathe through lungs. They spend most of their time in water but must come to the surface to breathe.

The thick skin of crocodilians is made up of bony plates. These animals have about 30 to 40 teeth in each jaw. The teeth lock together when their jaws are closed-kind of the way a zipper’s teeth fit together.

HUNTING AND EATING

Alligators and crocodiles float with their bodies almost totally underwater. Only their nostrils, eyes, and part of their backs stick out. They look scary as they silently stalk their prey (animals they hunt and eat).

Alligators and crocodiles have long, powerful tails. They sometimes swat prey with their tails. They also use their tails to push prey into deeper water, where it is easier to attack.

The powerful jaws of crocodilians slam shut on small animals and crush their bones. They eat fish, frogs, snakes, turtles, birds, and mammals. Crocodiles sometimes attack humans.

HUNTING AND EATING

Alligators and crocodiles make all kinds of sounds. They hiss softly. They make fearsome roars and bellows. Males roar and bellow loudest during the mating season. Scientists don’t know exactly what the roars mean. Maybe the males are trying to call females. Maybe they are trying to scare other males away.
SWIMMING AND WALKING

Alligators and crocodiles use their tails for swimming. They swish their strong tails back and forth.

On land, crocodilians sometimes crawl on their bellies. They can also gallop and walk fast on all four legs, just as many mammals do.

WHERE ALLIGATORS LIVE

There are two species (kinds) of alligators: the American alligator and the Chinese alligator. The American alligator lives mainly in swamps, lakes, and bayous in the southeastern United States. American alligators live as far west as the Rio Grande in Texas. The Chinese alligator lives along the Yangtze River in China.

Chinese alligators are much smaller than American alligators. They are usually less than 8 feet (2.5 meters) long. American alligators will attack people. Chinese alligators almost never attack people.
During cold winters, alligators bury themselves in mud. There they can hibernate until spring.

WHERE CROCODILES LIVE

Four species of crocodiles live in the Americas. These crocodiles are found in southern Florida, Cuba and other Caribbean islands, southern Mexico, Central America, and northern South America.

The Indo-Pacific crocodile lives along the seacoasts of India, southern China, Malaysia, and Australia. The swamp crocodile is found in the lakes and rivers of India. The Nile crocodile lives in parts of Africa.

LIFE CYCLE

Females crocodilians lay from 20 to 90 eggs. They lay their eggs in nests made of sand, mud, or rotting plant parts. Baby crocodilians hatch from the eggs.

Most female crocodilians watch over their young. Alligator mothers may help the babies break out of the egg. They sometimes carry the newborn alligators in their mouths. They put the babies into the water. Some mothers stay near their young for at least a year. If the young alligator gets in trouble, its mother is there to help.

No one is really sure how long alligators and crocodiles live. Scientists estimate that smaller species can live from 30 to 50 years, while larger crocodilian species can live to be 70 or even 80 years old.

THREATS TO CROCODILIANS

Alligators and crocodiles are threatened by hunting. People hunt them mainly for their eggs and for their skin. Many crocodile species are endangered.

The American alligator became an endangered species in 1967. Laws protected it from being hunted. As a result, the species made a comeback. By the late 1970s, people could again hunt the American alligator in some states.

Skin and Much More About Your Health

2011-06-13T03:00:00.000-07:00

Your skin is your body’s largest organ, larger than your heart or lungs or brain. Skin covers your whole body, from the top of your head to the soles of your feet. You could not live without your skin. Skin keeps germs and other harmful things out of your body. It keeps water, blood, and other fluids that you need inside your body.

You are always losing your skin and growing new skin. The outside layer of your skin is dead. It flakes off all the time. New skin grows to replace it.

LAYERS OF SKIN

Your skin has an outside layer called the epidermis. Under that is a layer called the dermis. Under those two layers is a layer of fat.

The epidermis protects the layers beneath it from minor scrapes, jabs, and sunburn. The bottom of your epidermis is always making new skin cells. The dead cells on the top of your skin are constantly dropping off.

The dermis is full of nerves and blood vessels. The nerves send signals to your brain when you touch something. The dermis gives your skin its toughness and strength. It also helps keep your body cool in hot weather and warm in cold weather. A scrape only bleeds if it’s deep enough to go through the epidermis and into the dermis.
There is a layer of fat under the dermis. This layer is thicker than both top layers of skin.

WHAT GIVES SKIN ITS COLOR?

The top layer of skin has a chemical called melanin. Melanin gives your skin its color. The more melanin you have, the darker your skin is. Patches of skin with extra melanin make freckles.

Melanin protects your skin from the Sun’s harmful rays. Your skin makes more melanin when you are out in the Sun. More melanin gives you a tan.

Melanin has its limits. Too much sunlight is bad for your skin. Harmful rays from the Sun can burn your skin. They can cause skin cancer.

WHAT IS HAIR MADE OF?

Hair is made of skin cells. A hair grows from a root under the skin. The hair grows up inside a shaft through the layers of skin. The part of the hair that you see is made of dead cells.

The color of hair, like the color of skin, comes from melanin. Melanin is made in the hair root. The hair of older people turns gray because the root stops making melanin.

The shape of the hair shaft gives you straight or curly hair. A round shaft makes straight hair. An oval-shaped shaft makes wavy hair. A comma-shaped shaft makes curly hair.

WHAT ARE FINGERNAILS MADE OF?

Fingernails and toenails are also made of skin cells. These nail cells are very hard. Nail cells start growing inside your fingers and toes. The cells die. New cells push the dead cells outward. This makes nails on your fingers and toes grow.

WHAT CAUSES PIMPLES?

Plugged pores cause pimples (zits). Pores are openings in the skin. Dead skin cells can plug up a pore. The plug can make a blackhead or a whitehead on top of the skin.

Pores allow oil to get to the surface of your skin. This oil is the kind that gives you oily skin, not the kind that gets made into gasoline. The oil keeps your skin and hair from drying out. Groups of cells called glands make the oil. Oil glands are almost everywhere in your body. There are many oil glands on your face and scalp.

The oil cannot get out of a plugged pore. Soon a pimple or a red lump forms. The red lumps can leave scars. Squeezing a pimple can cause a scar.

Doctors can help teenagers with lots of pimples. Doctors can give them medicine that will help make the pimples go away.

Have you ever scraped your knee or cut your finger? Scabs grow over scrapes, cuts, and other wounds that bleed. The blood dries and hardens. The blood turns into a scab.

New cells grow under the scab. The cells join up and cover the cut. When the skin is healed, the scab drops off.

DINOSAURS

2011-06-13T02:56:00.000-07:00

Imagine walking through a prehistoric forest and coming face to face with a terrifying dinosaur. This could never have happened, of course. People and dinosaurs did not live on Earth at the same time. Dinosaurs died out long before people appeared. Dinosaurs lived from about 230 million years ago to about 65 million years ago.
HOW DO WE KNOW ABOUT DINOSAURS?
Paleontologists (scientists who study prehistoric life) learn about dinosaurs by studying fossils of their bones. These fossils are the remains of dead animals that have turned into rock.
People probably found fossils of dinosaur bones thousands of years ago but did not know what the bones were. In the early 1800s, people realized that the fossil bones belonged to prehistoric animals. The first dinosaurs that paleontologists studied were named Megalosaurus and Iguanodon. The bones looked like those of reptiles, such as lizards. The flat teeth of Iguanodon showed that it was a plant eater. The pointy teeth of Megalosaurus showed that it was a meat eater.
The early fossils came from England. British scientist Sir Richard Owen in 1842 named these animals dinosaurs. The word comes from two Greek words meaning “terrible” and “lizard.” Scientists now know that dinosaurs were not lizards.
KINDS OF DINOSAURS
Paleontologists have found fossils of hundreds of different kinds of dinosaurs that lived all over the world. Some dinosaurs were small like birds. Other dinosaurs were much bigger than an elephant.
Paleontologists divide dinosaurs into two groups, or orders, by the way their hips looked. One group had hips that were like birds’ hips. They called this order Ornithischia. The other group had hips like those of lizards. They called this order Saurischia.
There were three basic kinds of dinosaurs in the Saurischia order: theropods, prosauropods, and sauropods. There were five basic kinds of dinosaurs in the Ornithischia order: stegosaurs, ankylosaurs, ornithopods, pachycephalosaurs, and ceratopsians.
THEROPODS
All dinosaurs were plant eaters except for theropods. Theropods were meat eaters that hunted plant-eating dinosaurs and smaller theropods. Most theropods walked on their two hind legs. One of the most famous theropods is Tyrannosaurus rex. This dinosaur was about 39 feet (12 meters) long and weighed 5 metric tons.
Some theropods were called raptors. Velociraptor and other raptors had powerful claws, like the claws of an eagle. These dinosaurs probably hunted in packs.
PROSAUROPODS
Prosauropods had spoon-shaped teeth and long, slender necks. These large, plant-eating dinosaurs stood on two legs and grazed on tall bushes and trees. One type of prosauropod, Plateosaurus, was 30 feet (9 meters) long and weighed 1.8 metric tons.
SAUROPODS
Sauropods descended from prosauropods. Some of the best-known sauropods were Apatosaurus and Diplodocus. These dinosaurs had thick legs and feet like elephants’ feet, but with claws. They walked on four legs. At one time sauropods were the biggest dinosaurs on Earth. Some sauropods may have been more than 82 feet (25 meters) long and weighed about 90 metric tons.
STEGOSAURS
These ornithischians walked on four legs and had a row of bony plates down their back. Stegosaurus, a large stegosaur, also had spikes on its tail. It used its spiked tail for fighting off meat-eating theropods. Stegosaurus was about 30 feet (9 meters) long.
ANKYLOSAURS
These dinosaurs were covered with bony plates that acted as body armor to protect them against theropods. Some had a bony plate in each eyelid and large clubs on their tails. Bony rings and spines protected their necks. Ankylosaurus was about 33 feet (10 meters) long.
ORNITHOPODS
Ornithopods were once the most numerous plant-eating dinosaurs. There were many different kinds. Over time, ornithopods developed broad beaks. These later ornithopods are called duck-billed dinosaurs. Some ornithopods were small and ran fast. Others were huge. Iquanodon, for example, was 25 feet (7.5 meters) long.
PACHYCEPHALOSAURS
These dinosaurs walked on two feet. They had thick, dome-shaped skulls. Scientists think they may have used their thick heads to butt other dinosaurs.
CERATOPSIANS
These dinosaurs ware also called horned dinosaurs. One of the best-known ceratopsians was Triceratops. It had three horns on the top of its head: one horn on its snout and one horn above each eye. Triceratops could reach lengths of up to 26 feet (8 meters) and weighed more than 12 metric tons.
WHAT HAPPENED TO THE DINOSAURS?
There are several theories about why dinosaurs died out. Many scientists believe that there was a sudden, violent event. They think that an asteroid or comet collided with Earth. Fire from the impact burned large areas. Dust blocked sunlight from reaching the surface of Earth. Acid rain fell everywhere. Plants could not grow. There was no food for the plant-eating dinosaurs, so they died out. Dinosaurs that ate plant-eating animals also died out.
Other scientists think that the environment changed. Maybe the climate grew colder and dinosaurs slowly became extinct over several million years.
Many scientists think that birds descended from a small kind of dinosaur. If this is true, then dinosaurs, in a sense, are still alive in the form of modern birds.

WHY DO WE DANCE?

2011-06-13T02:53:00.000-07:00

Have you ever twirled in a circle? Stretched on your tiptoes and swept your arms above your head? Tapped your feet to snappy music? All people dance, because the human body is made to move. The world offers an exciting variety of dances!

WHAT IS DANCE?
Our bodies can twist, jump, stretch, and turn. Dance blends these movements together, usually with music. Dance uses space: What patterns do the dancers make across the floor? What designs do dancers’ arms and legs brush through the air? Dance uses time: Is the dance fast or slow? What rhythm pulses in the music? Dance uses weight: Are the steps light and quick, or heavy and limp? Dance uses energy: Does the dance have fast, choppy movements, or flowing, soft ones?
WHY DO WE DANCE?
People around the world dance for different reasons and in different ways. Some dances can express feelings like sadness, anger, or joy. Other dances can tell a story.
Dance may sparkle as an art form, as ballet does, and be performed for an audience. Ballet dancers train for years to learn to leap and turn across a stage.
People may dance as part of an important ceremony, even as part of their religion. Some cultures honor their ancestors through dance. Dances may celebrate important events, such as a birth, graduation, or marriage. A dance might be used to help work go faster, as in the Japanese rice-planting dance.
In some cultures a shaman, or healer, might dance to cure an illness. Some societies use dance to reach a state of trance so the dancers can perform acts of strength or courage, such as dancing on hot coals.
DANCING FOR FUN
We may gather together and dance simply for fun. Many countries have group dances-folk dances-that are passed down through generations.
Social dances encourage two people to dance together. These dances come and go: A new dance may be very popular one year, and out of fashion the next. In the 1800s, couples glided through a waltz or polka. Young people kicked up their heels doing the Charleston in the 1920s. Teenagers spun and swung to the 1940s jitterbug. Couples did not even have to touch hands for the 1960s dance craze, the twist. Disco dancing, popular in the 1970s, and today’s hip-hop are also social dances.
HOW LONG HAVE PEOPLE DANCED?
Dance probably has been around about as long as people have. Cave paintings thousands of years old show what look like dancing figures. Dancers appear in the art of ancient Egypt and Greece. Through dance, societies asked their gods for good crops or bravery in battle.
Hundreds of years ago the Christian church frowned upon dancing. But farmers and villagers still danced for fun. Many of these dances developed into folk dances. Ballet grew out of dances at the royal courts of France and Italy in the 1500s and 1600s.
Drama, acrobatics, and music are combined with dance in many cultures. People added makeup, costumes, and masks to turn dance into theater. These performances tell a story using movements rather than words.
HOW WILL DANCE CHANGE IN THE FUTURE?
Dance constantly evolves, or changes. People seek new forms of expression. Cultures borrow from one another, and from the past. Latin American dance blends Spanish and Native American styles. African and Asian dances influence dance in Europe and North America.
Like our ancestors long ago, we dance for important ceremonies. And like our ancestors, we also dance for the joy of movement, to express our emotions, and to share music and fun.

What is Money?

2011-06-09T04:52:00.000-07:00

Why is a dollar bill valuable? After all, you can’t eat it. You can’t wear it. It’s just a piece of paper. But you can trade dollars for things that you can eat or wear. The bills are worth something because everyone agrees that they have value.

WHAT IS MONEY?
Money is anything that is widely exchanged for goods people sell or work they do. It is a form of payment people will accept. Long ago, precious metals such as gold and silver were used as money. Today, paper bills and coins are a common form of money.
Money has other uses, too. One of them is to measure the value of things. Bicycles, clothes, even hamburgers have a certain value. That value is the price-how much money people will pay for it.
Money is also a way people store up wealth. People save their money in bank accounts or piggy banks. Saving money is a way of collecting and storing wealth, much like owning land, a home, or jewelry.
MONEY AROUND THE WORLD
Most countries have their own unit of money. The money used by a country is called its currency.
In the United States, the basic unit of money, or currency, is the dollar. Each dollar is divided into 100 cents. The value of anything you want to buy in the United States can be stated in dollars and cents.
Other countries have their own currencies. In the United Kingdom, the value of things is measured in money units called pounds, not dollars. Algerians use neither pounds nor dollars, but dinars. Indians and Pakistanese use rupees. Mexicans use pesos. Russians use rubles.
MANY KINDS OF MONEY
Money is more than just paper bills and metal coins. It can be just about anything, as long as everyone agrees.
Over the course of history, many items have been used as money. Shells, beads, furs, salt-even the teeth of dogs-have all been used as money. They were used much like we use bills and coins today.
HOW WAS MONEY INVENTED?
No one person came up with the idea of money. The idea developed slowly. Before money was invented, people traded goods using the barter system.
In the barter system, people trade things for other things directly. Suppose a man had a sheep and wanted clothes. He found someone with an extra suit of clothes who wanted a sheep.
But what if he only wanted a shirt? He might not want to trade his entire sheep for just one shirt. How could he get change for a sheep? Problems like this made bartering difficult. People invented money to make trading easier.
METALS AS MONEY
Eventually, people found they could use precious metals such as gold, silver, or copper to help them trade. Almost everyone wanted these metals. So people could trade what they had for precious metals, knowing they could exchange the metal for something else they wanted or needed.
Metals had other benefits, too. They were easy to store, lasted a long time, and could easily be divided into smaller pieces. If you wanted something small, you could offer just a bit of your metal.
COINS AND BILLS
Once people started trading metals as money, coins were soon invented. A Turkish kingdom called Lydia made the first metal coins around 600 bc. The coins were stamped with the king’s seal. About the same time, people in China began to use paper money.
In the past, paper money often stood for a precious metal like gold. You could go to the government or a bank and trade your paper bills for actual gold.
Today, in most countries, you can’t trade paper money for precious metals. People accept it because they have confidence everyone else will accept it, too.

Unidentified Flying Object

2011-06-09T04:38:00.000-07:00

You’re watching the sky after dark. It’s a clear night. Many stars are visible. Suddenly you see a streak of light. Perhaps it’s a shooting star. As you watch, it slows down. Now it’s a moving point of light. Maybe it’s a plane or a space shuttle. You see it slow to a stop.
Half a minute passes. Just when you think you’re looking at an ordinary star, it suddenly speeds away. In seconds, it disappears over the horizon.
Have you seen an unidentified flying object? Most certainly. Was it a spaceship from another planet? Almost certainly not.
WHAT UFOS ARE-AND ARE NOT
An unidentified flying object (UFO) is any light or object seen in the sky that can’t be explained. Hundreds of UFO sightings are reported every year. More than nine-tenths of them are later identified as ordinary objects. They might be planes, satellites, or planets. They might be balloons, kites, clouds, or birds. Some are deliberate fakes.
But some UFOs remain unidentified. So some people believe that they come from other planets. Some even claim to have met aliens and been brought aboard their spacecraft.
It is indeed possible that intelligent life might exist somewhere beyond the solar system. But no one has ever produced proof of visitors from outer space. No photograph of a spaceship has ever been accepted as genuine.
PROJECT BLUE BOOK
UFOs have been reported since ancient times. Modern reports of UFO sightings began in 1947. Some observers reported seeing saucer-like shapes in the sky. Since then, UFOs of any shape are often called flying saucers.
The United States Air Force took these reports seriously. Air Force officials did not necessarily believe in visitors from outer space. They wanted to be sure that UFOs were not a threat to our country. A UFO might, for example, be an enemy airplane.
Project Blue Book was the Air Force’s program for investigating UFOs. It ran from 1947 through 1969. The Air Force investigated 12,618 UFO sightings. All but 701 were identified.
The Air Force concluded that UFOs were no threat. All sightings could be explained by science. There was no evidence that UFOs came from other planets.
WHAT ARE YOU REALLY SEEING?
In 1997, the United States government released some information. It had been operating high-flying spy planes. These flights were secret. More than half the UFOs reported during the 1950s and 1960s were these planes.
Many UFOs appear in the sky opposite the Sun. Their shapes may appear strange. But they’re actually ordinary objects that reflect the Sun’s rays. They often prove to be planes or balloons. The vapor trails of jet planes can take on odd shapes. They can look like saucers. They may appear to hang motionless in the sky. Such appearances can fool even experienced scientists.
If you see a UFO, look at it carefully. Note what time it is. Where are you? In what direction does the object appear in the sky? Sketch the UFO’s shape. Does it change as it moves? Such careful observation can usually identify a UFO.