Tree

A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance.[1] A minimum height specification at maturity is cited by some authors, varying from 3 m[2] to 6 m;[3] some authors set a minimum of 10 cm trunk diameter (30 cm girth).[4] Woody plants that do not meet these definitions by having multiple stems and/or small size, are called shrubs. Compared with most other plants, trees are long-lived, some reaching several thousand years old and growing to up to 115 m (379 ft) high.[5]

Trees are an important component of the natural landscape because of their prevention of erosion and the provision of a weather-sheltered ecosystem in and under their foliage. Trees also play an important role in producing oxygen and reducing carbon dioxide in the atmosphere, as well as moderating ground temperatures. They are also elements in landscaping and agriculture, both for their aesthetic appeal and their orchard crops (such as apples). Wood from trees is a building material, as well as a primary energy source in many developing countries. Trees also play a role in many of the world's mythologies (see trees in mythology). 

A tree is a plant form that occurs in many different orders and families of plants. Trees show a variety of growth forms, leaf type and shape, bark characteristics, and reproductive organs. The tree form has evolved separately in unrelated classes of plants, in response to similar environmental challenges, making it a classic example of parallel evolution. With an estimate of 100,000 tree species, the number of tree species worldwide might total 25 percent of all living plant species.[7] The majority of tree species grow in tropical regions of the world and many of these areas have not been surveyed yet by botanists, making species diversity and ranges poorly understood.[8]

The earliest trees were tree ferns, horsetails and lycophytes, which grew in forests in the Carboniferous Period; tree ferns still survive, but the only surviving horsetails and lycophytes are not of tree form. Later, in the Triassic Period, conifers, ginkgos, cycads and other gymnosperms appeared, and subsequently flowering plants in the Cretaceous Period. Most species of trees today are flowering plants (Angiosperms) and conifers. For the listing of examples of well-known trees and how they are classified, see List of tree genera.

Plants

Plants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. About 350,000 species of plants, defined as seed plants, bryophytes, ferns and fern allies, are estimated to exist currently. As of 2004, some 287,655 species had been identified, of which 258,650 are flowering and 18,000 bryophytes (see table below). Green plants, sometimes called metaphytes or viridiplantae, obtain most of their energy from sunlight via a process called photosynthesis.

Aristotle divided all living things between plants (which generally do not move), and animals (which often are mobile to catch their food). In Linnaeus' system, these became the Kingdoms Vegetabilia (later Metaphyta or Plantae) and Animalia (also called Metazoa). Since then, it has become clear that the Plantae as originally defined included several unrelated groups, and the fungi and several groups of algae were removed to new kingdoms. However, these are still often considered plants in many contexts, both technical and popular.

When the name Plantae or plants is applied to a specific taxon, it is usually referring to one of three concepts. From smallest to largest in inclusiveness, these three groupings are: Informally, other creatures that carry out photosynthesis are called plants as well, but they do not constitute a formal taxon and represent species that are not closely related to true plants. There are around 375,000 species of plants, and each year more are found and described by science.

Most algae are no longer classified within the Kingdom Plantae.[2][3] The algae comprise several different groups of organisms that produce energy through photosynthesis, each of which arose independently from separate non-photosynthetic ancestors. Most conspicuous among the algae are the seaweeds, multicellular algae that may roughly resemble terrestrial plants, but are classified among the green, red, and brown algae. Each of these algal groups also includes various microscopic and single-celled organisms.

Musical instrument

A musical instrument is a device constructed or modified for the purpose of making music. In principle, anything that produces sound can serve as a musical instrument. The term "musical instrument", however, is generally reserved for items that have a specific musical purpose such as a piano. The academic study of musical instruments is called organology.

Scholars agree that there are no completely reliable methods of determining the exact chronology of musical instruments across cultures. Comparing and organizing instruments based on their complexity is misleading, since advancements in musical instruments have sometimes reduced complexity. For example, construction of early slit drums involved felling and hollowing out large trees; later slit drums were made by opening bamboo stalks, a much simpler task.[1] It is likewise misleading to arrange the development of musical instruments by workmanship since all cultures advance at different levels and have access to different materials. For example, anthropologists attempting to compare musical instruments made by two cultures that existed at the same time but who differed in organization, culture, and handicraft cannot determine which instruments are more "primitive".[2] Ordering instruments by geography is also partially unreliable, as one cannot determine when and how cultures contacted one another and shared knowledge. German musicologist Curt Sachs, one of the most prominent musicologists in modern times,[3] proposed that a geographical chronology is preferable, however, due to its limited subjectivity.[4]

Archaeological evidence of musical instruments was discovered in excavations at the Royal Cemetery in the Sumerian city of Ur. These instruments include nine lyres, two harps, a silver double flute, sistra and cymbals. These excavations, carried out by Leonard Woolley in the 1920s, uncovered non-degradable fragments of instruments and the voids left by the degraded segments which, together, have been used to reconstruct them.[5] The graves to which these instruments were related have been carbon dated to between 2600 and 2500 BCE, providing evidence that these instruments were being used in Sumeria by this time.[6]

A cuneiform tablet from Nippur in Mesopotamia dated to 2000 BCE indicates the names of strings on the lyre and represents the earliest known example of music notation.[7] Until the 19th century AD, written music histories began with mythological accounts of how musical instruments were invented. Such accounts included Jubal, descendant of Cain and "father of all such as handle the harp and the organ", musical instrument" is completely subjective to both the scholar and the would-be inventor. For example, a Homo habilis slapping his body could be the makings of a musical instrument regardless of the being's intent. 

Toy

A toy is an object used in play. Toys are usually associated with children and pets, but it is not unusual for adult humans and some non-domesticated animals to play with toys. Many items are manufactured to serve as toys, but items produced for other purposes can also be used as toys. A child may pick up a household item and 'fly' it around pretending that it is an airplane, or an animal might play with a pinecone by batting at it, biting it, chasing it, or by throwing it up in the air. Some toys are produced primarily as collector's items and are not intended to be played with.

The origin of toys is prehistoric; dolls representing infants, animals, and soldiers, as well as representations of tools used by adults are readily found at archaeological sites. The origin of the word "toy" is unknown, but it is believed that it was first used in the 14th century.[1] Toys, and play in general, are important when it comes to growing up and learning about the world around us. The young use toys and play to discover their identity, help their bodies grow strong, learn cause and effect, explore relationships, and practice skills they will need as adults. Adults use toys and play to form and strengthen social bonds, teach, remember and reinforce lessons from their youth, discover their identity, exercise their minds and bodies, explore relationships, practice skills, and decorate their living spaces.

Toys are more than simple amusement, they and the ways that they are used profoundly influence many aspects of life.[ Most young mammals will play with whatever they can find, turning such things as pinecones, rocks, and food into toys. It simply makes sense then that toys have a history as old as human civilization itself. Toys and games have been unearthed from the sites of ancient civilizations. They have been written about in some of our oldest literature. Toys excavated from the Indus valley civilization (3000-1500 BCE) include small carts, whistles shaped like birds, and toy monkeys which could slide down a string.[2]

The earliest toys were made from materials found in nature, such as rocks, sticks, and clay. Thousands of years ago, Egyptian children played with dolls that had wigs and movable limbs which were made from stone, pottery, and wood.[3] In Ancient Greece and Ancient Rome, children played with dolls made of wax or terra cotta, sticks, bows and arrows, and yo-yos. When Greek children, especially girls, came of age it was customary for them to sacrifice the toys of their childhood to the gods. On the eve of their wedding, young girls around fourteen would offer their dolls in a temple as a rite of passage into adulthood.[4][5]

Art

Art is the process or product of deliberately arranging elements in a way that appeals to the sense or emotions. Art encompasses a diverse range of human activities, creations, and modes of expression, including music and literature. Aesthetics is the branch of philosophy which studies art. Traditionally, the term art was used to refer to any skill or mastery. This conception changed during the Romantic period, when art came to be seen as "a special faculty of the human mind to be classified with religion and science".[1] Generally art is made with the intention of stimulating thoughts and emotions.

Visual art is defined as the arrangement of colors, forms, or other elements "in a manner that affects the sense of beauty, specifically the production of the beautiful in a graphic or plastic medium".[2] The nature of art has been described by Wollheim as "one of the most elusive of the traditional problems of human culture".[3] The most common usage of the word "art," which rose to prominence after 1750, is understood to denote skill used to produce an aesthetic result.[7] Britannica Online defines it as "the use of skill and imagination in the creation of aesthetic objects, environments, or experiences that can be shared with others."[8] 

By any of these definitions of the word, artistic works have existed for almost as long as humankind: from early pre-historic art to contemporary art; however, some theories restrict the concept to modern Western societies.[9] Much has been written about the concept of "art".[10] Where Adorno said in 1970 "It is now taken for granted that nothing which concerns art can be taken for granted any more[...],"[11],[12] The first and broadest sense of art is the one that has remained closest to the older Latin meaning, which roughly translates to "skill" or "craft," and also from an Indo-European root meaning "arrangement" or "to arrange". 

The second and more recent sense of the word art is as an abbreviation for creative art or fine art. Fine art means that a skill is being used to express the artist’s creativity, or to engage the audience’s aesthetic sensibilities, or to draw the audience towards consideration of the finer things. Often, if the skill is being used in a common or practical way, people will consider it a craft instead of art. Likewise, if the skill is being used in a commercial or industrial way, it will be considered Commercial art instead of fine art. On the other hand, crafts and design are sometimes considered applied art. Some art followers have argued that the difference between fine art and applied art has more to do with value judgments made about the art than any clear definitional difference.[13] However, even fine art often has goals beyond pure creativity and self-expression. sense of beauty (see aesthetics); to explore the nature of perception; for pleasure; or to generate strong emotions. The purpose may also be seemingly nonexistent.

Animation

Animation is the rapid display of a sequence of images of 2-D or 3-D artwork or model positions in order to create an illusion of movement. It is an optical illusion of motion due to the phenomenon of persistence of vision, and can be created and demonstrated in a number of ways. The most common method of presenting animation is as a motion picture or video program, although several other forms of presenting animation also exist.

Early examples of attempts to capture the phenomenon of motion drawing can be found in paleolithic cave paintings, where animals are depicted with multiple legs in superimposed positions, clearly attempting to convey the perception of motion. A 5,200 year old earthen bowl found in Iran in Shahr-i Sokhta has five images of a goat painted along the sides.This has been claimed to be an example of early animation.[1][2][3] However, since no equipment existed to show the images in motion, such a series of images cannot be called animation in a true sense of the word.[4][5]

The phenakistoscope, praxinoscope, as well as the common flip book were early popular animation devices invented during the 1800s, while a Chinese zoetrope-type device was invented already in 180 AD.[6][7][8][9] These devices produced movement from sequential drawings using technological means, but animation did not really develop much further until the advent of cinematography. There is no single person who can be considered the "creator" of the art of film animation, as there were several people doing several projects which could be considered various types of animation all around the same time.

Georges Méliès was a creator of special-effect films; he was generally one of the first people to use animation with his technique. He discovered a technique by accident which was to stop the camera rolling to change something in the scene, and then continue rolling the film. This idea was later known as stop-motion animation. Méliès discovered this technique accidentally when his camera broke down while shooting a bus driving by. When he had fixed the camera, a hearse happened to be passing by just as Méliès restarted rolling the film, his end result was that he had managed to make a bus transform into a hearse. This was just one of the great contributors to animation in the early years.

Sun

The Sun (Latin: Sol), a yellow dwarf, is the star at the center of the Solar System. The Earth and other matter (including other planets, asteroids, meteoroids, comets, and dust) orbit the Sun,[9] which by itself accounts for about 99.8% of the Solar System's mass. The mean distance of the Sun from the Earth is approximately 149,600,000 kilometers, or 92,960,000 miles, and its light travels this distance in 8.3 minutes. Energy from the Sun, in the form of sunlight, supports almost all life on Earth via photosynthesis, and drives the Earth's climate and weather.

The surface of the Sun consists of hydrogen (about 74% of its mass, or 92% of its volume), helium (about 24% of mass, 7% of volume), and trace quantities of other elements, including iron, nickel, oxygen, silicon, sulfur, magnesium, carbon, neon, calcium, and chromium.[10] The Sun has a spectral class of G2V. G2 means that it has a surface temperature of approximately 5,780 K (5,500 C) giving it a white color that often, because of atmospheric scattering, appears yellow when seen from the surface of the Earth. This is a subtractive effect, as the preferential scattering of shorter wavelength light removes enough violet and blue light, leaving a range of frequencies that is perceived by the human eye as yellow. It is this scattering of light at the blue end of the spectrum that gives the surrounding sky its color. When the Sun is low in the sky, even more light is scattered so that the Sun appears orange or even red.[11]

The Sun's spectrum contains lines of ionized and neutral metals as well as very weak hydrogen lines. The V (Roman five) in the spectral class indicates that the Sun, like most stars, is a main sequence star. This means that it generates its energy by nuclear fusion of hydrogen nuclei into helium. There are more than 100 million G2 class stars in our galaxy. Once regarded as a small and relatively insignificant star, the Sun is now known to be brighter than 85% of the stars in the galaxy, most of which are red dwarfs.[12]

The Sun orbits the center of the Milky Way galaxy at a distance of approximately 24,000 to 26,000 light years from the galactic center, moving generally in the direction of Cygnus and completing one revolution in about 225–250 million years (one Galactic year). Its orbital speed was thought to be 220±20 km/s, but a new estimate gives 251 km/s[13]. This is equivalent to about one light-year every 1,190 years, and about one AU every 7 days. These measurements of galactic distance and speed are as accurate as we can get given our current knowledge, but may change as we learn more.[14] Since our galaxy is moving with respect to the cosmic microwave background radiation (CMB) in the direction of Hydra with a speed of 550 km/s, the sun's resultant velocity with respect to the CMB is about 370 km/s in the direction of Crater or Leo.[15]

Planet

A planet, as defined by the International Astronomical Union (IAU), is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.[a][1][2]

The term planet is ancient, with ties to history, science, myth, and religion. The planets were originally seen by many early cultures as divine, or as emissaries of the gods. Even today, many people believe in astrology, which holds that the movement of the planets affects people's lives, although such a causation is rejected by the scientific community. As scientific knowledge advanced, human perception of the planets changed, incorporating a number of disparate objects. Even now there is no uncontested definition of what a planet is. In 2006, the IAU officially adopted a resolution defining planets within the Solar System. This definition has been both praised and criticized, and remains disputed by some scientists.

The planets were thought by Ptolemy to orbit the Earth in deferent and epicycle motions. Though the idea that the planets orbited the Sun had been suggested many times, it was not until the 17th century that this view was supported by evidence from the first telescopic astronomical observations, performed by Galileo Galilei. By careful analysis of the observation data, Johannes Kepler found the planets' orbits to be not circular, but elliptical. As observational tools improved, astronomers saw that, like Earth, the planets rotated around tilted axes, and some share such features as ice-caps and seasons. Since the dawn of the Space Age, close observation by probes has found that Earth and the other planets share characteristics such as volcanism, hurricanes, tectonics, and even hydrology. Since 1992, through the discovery of hundreds of extrasolar planets (planets around other stars), scientists are beginning to understand that planets throughout the Milky Way Galaxy share characteristics in common with our own.

Planets are generally divided into two main types: large, low-density gas giants, and smaller, rocky terrestrials. Under IAU definitions, there are eight planets in the Solar System. In order from the Sun, they are the four terrestrials, Mercury, Venus, Earth, and Mars, then the four gas giants, Jupiter, Saturn, Uranus, and Neptune. Many of these planets are orbited by one or more moons, which can be larger than small planets. As of January 13th 2009, there are 335 known extrasolar planets, ranging from the size of gas giants to that of terrestrial planets.[3] This brings the total number of identified planets to at least 343. The Solar System also contains at least five dwarf planets: Ceres, Pluto (formerly considered to be the Solar System's ninth planet), Makemake, Haumea and Eris. No extrasolar dwarf planets have yet been detected.

Medicine

Medicine is the art and science of healing. It encompasses a range of health care practices evolved to maintain and restore health by the prevention and treatment of illness. Early records on medicine have been discovered from early Ayurvedic medicine in the Indian subcontinent, ancient Egyptian medicine, traditional Chinese medicine, the Americas, and ancient Greek medicine. Early Grecian doctors Hippocrates, who is also called the Father of Medicine,[4][5] and Galen laid a foundation for later developments in a rational approach to medicine. After the fall of Rome and the onset of the Dark Ages.

Islamic physicians made major medical breakthroughs, supported by the translation of Hippocrates' and Galen's works into Arabic. Notable Islamic medical pioneers include polymath Avicenna, who is also called the Father of Modern Medicine,[6][7] Abulcasis, the father of surgery, Avenzoar, the father of experimental surgery, Ibn al-Nafis, the father of circulatory physiology, and Averroes.[8] Rhazes, who is called the father of pediatrics, first disproved the Grecian theory of humorism, which nevertheless remained influential in Western medieval medicine. While major developments in medicine were occurring in the Islamic world during the medieval period, the Western world remained dependent upon the Greco-Roman theory of humorism, which led to questionable treatments such as bloodletting. 

Islamic medicine and medieval medicine collided during the crusades, with Islamic doctors receiving mixed impressions.[9] As the medieval ages ended, important early figures in medicine emerged in Europe, including Gabriele Falloppio and William Harvey. The major shift in medical thinking was the gradual rejection, especially during the Black Death in the 14th and 15th centuries, of what may be called the 'traditional authority' approach to science and medicine. This was the notion that because some prominent person in the past said something must be so, then that was the way it was, and anything one observed to the contrary was an anomaly (which was paralleled by a similar shift in European society in general - see Copernicus's rejection of Ptolemy's theories on astronomy). Physicians like 

Modern scientific biomedical research (where results are testable and reproducible) began to replace early Western traditions based on herbalism, the Greek "four humours" and other such pre-modern notions. The modern era really began with Robert Koch's discoveries around 1880 of the transmission of disease by bacteria, and then the discovery of antibiotics around 1900. The post-18th century modernity period brought more groundbreaking researchers from Europe. From Germany and Austrian doctors such as Rudolf Virchow, Wilhelm Conrad Röntgen, Karl Landsteiner, and Otto Loewi) made contributions. In the United Kingdom Alexander Fleming, Joseph Lister, Francis Crick, and Florence Nightingale are considered.

Baseball

Baseball is a bat-and-ball sport played between two teams of nine players each. The goal of baseball is to score runs by hitting a thrown ball with a bat and touching a series of four markers called bases arranged at the corners of a ninety-foot square, or diamond. Players on one team (the batting team) take turns hitting while the other team (the fielding team) tries to stop them from scoring runs by getting hitters out in any of several ways. A player on the batting team can stop at any of the bases and hope to score on a teammate's hit. The teams switch between batting and fielding whenever the fielding team gets three outs. One turn at bat for each team constitutes an inning; nine innings make up a professional game. The team with the most runs at the end of the game wins.

Evolving from older bat-and-ball games, an early form of baseball was being played in England by the mid-eighteenth century. This game, as well as the related game of rounders, were brought by British and Irish immigrants to North America, where the modern version of baseball developed. By the late nineteenth century, baseball was widely recognized as the national sport of the United States. Baseball on the professional, amateur, and youth levels is now popular in North America, Central America, parts of South America and the Caribbean, and parts of East Asia and Southeast Asia.

In North America, professional Major League Baseball teams are divided into the National League (NL) and American League (AL). Each league has three divisions: East, West, and Central. Every year, the champion of Major League Baseball is determined by playoffs culminating in the World Series. Four teams make the playoffs from each league: the three regular season division winners, plus one wild card team. The wild card is the team with the best record among the non–division winners in the league. In the National League, the pitcher is required to bat, per the traditional rules. In the American League, there is a tenth player, a designated hitter, who bats for the pitcher. Each major league team has a "farm system" of minor league teams at various levels. 

The distinct evolution of baseball from among the various bat-and-ball games is difficult to trace with precision. A French manuscript from 1344 contains an illustration of clerics playing a game, possibly la soule, with certain similarities to baseball; two other old French games, théque and la balle empoisonée, also appear to be related.[1] Consensus used to hold that today's baseball is a North American development from the older game rounders, popular in Great Britain and Ireland. However a 2005 book.

Basketball

Basketball is a team sport in which two teams of five active players each try to score points against one another by propelling a ball through a 10 feet (3 m) high hoop (the goal) under organized rules. Basketball is one of the most popular and widely viewed sports in the world.[1] Points are scored by shooting the ball through the basket above; the team with more points at the end of the game wins. The ball can be advanced on the court by bouncing it (dribbling) or passing it between teammates. Disruptive physical contact (foul) is not permitted and there are restrictions on how the ball can be handled (violations).

Through time, basketball has developed to involve common techniques of shooting, passing and dribbling, as well as players' positions, and offensive and defensive structures. Typically, the tallest members of a team will play center or one of two forward positions, while shorter players or those who possess the best ball handling skills and speed, play the guard positions. While competitive basketball is carefully regulated, numerous variations of basketball have developed for casual play. In some countries, basketball is also a popular spectator sport.While competitive basketball is primarily an indoor sport, played on a basketball court, less regulated variations have become exceedingly popular as an outdoor sport among both inner city and rural groups.

In early December 1891, Dr. James Naismith,[2] a Canadian physical education professor from McGill University of Montréal and instructor at YMCA Training School[3] (today, Springfield College) in Springfield, Massachusetts, USA, sought a vigorous indoor game to keep his students occupied and at proper levels of fitness during the long New England winters. After rejecting other ideas as either too rough or poorly suited to walled-in gymnasiums, he wrote the basic rules and nailed a peach basket onto a 10-foot (3.05 m) elevated track. In contrast with modern basketball nets, this peach basket retained its bottom, and balls had to be retrieved manually after each "basket" or point scored; this proved inefficient, however, so a hole was drilled into the bottom of the basket, allowing the balls to be poked out with a long dowel each time. The peach baskets were used until 1906 when they were finally replaced by metal hoops with backboards. A further change was soon made, so the ball merely passed through, paving the way for the game we know today.

 A soccer ball was used to shoot goals. Whenever a person got the ball in the basket, his team would gain a point. Whichever team got the most points won the game.[4] The baskets were originally nailed to the mezzanine balcony of the playing court, but this proved impractical when spectators on the balcony began to interfere with shots. The backboard was introduced to prevent this interference; it had the additional effect of allowing rebound shots.[5]  

Chess

Chess is a recreational and competitive game played between two players. Sometimes called Western chess or international chess to distinguish it from its predecessors and other chess variants, the current form of the game emerged in Southern Europe during the second half of the 15th century after evolving from similar, much older games of Indian and Persian origin. Today, chess is one of the world's most popular games, played by millions of people worldwide at home, in clubs, online, by correspondence, and in tournaments.

The game is played on a square chequered chessboard with 64 squares arranged in an eight-by-eight grid. At the start, each player (one controlling the white pieces, the other controlling the black pieces) controls sixteen pieces: one king, one queen, two rooks, two knights, two bishops, and eight pawns. The object of the game is to checkmate the opponent's king, whereby the king is under immediate attack (in "check") and there is no way to remove it from attack on the next move.

The tradition of organized competitive chess started in the 16th century and has developed extensively. Chess today is a recognized sport of the International Olympic Committee. The first official World Chess Champion, Wilhelm Steinitz, claimed his title in 1886; Viswanathan Anand is the current World Champion. Theoreticians have developed extensive chess strategies and tactics since the game's inception. Aspects of art are found in chess composition. One of the goals of early computer scientists was to create a chess-playing machine. Today's chess is deeply influenced by the abilities of current chess programs and the ability to play against others online. In 1997, Deep Blue became the first computer to beat the reigning World Champion in a match when it defeated Garry Kasparov.

Chess is played on a square board of eight rows (called ranks and denoted with numbers 1 to 8) and eight columns (called files and denoted with letters a to h) of squares. The colors of the sixty-four squares alternate and are referred to as "light squares" and "dark squares". The chessboard is placed with a light square at the right hand end of the rank nearest to each player, and the pieces are set out as shown in the diagram, with each queen on its own color.

Cricket

Cricket is a bat-and-ball team sport that originated in England, possibly as early as 1300, and is now played in more than 100 countries.[citation needed] There are several forms of cricket, at its highest level is Test cricket, in which the current world leading team is Australia,[1] followed by One Day International cricket, whose last World Cup was also won by Australia; the tournament was televised in over 200 countries to a viewing audience estimated at more than two billion viewers.[2][3]

A cricket match is contested by two teams, usually of eleven players each[4] and is played on a grass field in the centre of which is a flat strip of ground 22 yards (20 m) long called a pitch. A wicket, usually made of wood, is placed at each end of the pitch and used as a target. The bowler, a player from the fielding team, bowls a hard leather, fist-sized, 5.5 ounces (160 g) cricket ball from the vicinity of one wicket towards the other, which is guarded by the batsman, a player from the opposing team. The ball usually bounces once before reaching the batsman. In defence of his wicket, the batsman plays the ball with a wooden cricket bat. Meanwhile, the other members of the bowler's team stand in various positions around the field as fielders, players who retrieve the ball in an effort to stop the batsman scoring runs, and if possible to get him or her out. The batsman — if he or she does not get out — may run between the wickets, exchanging ends with a second batsman (the "non-striker"), who has been stationed at the other end of the pitch. Each completed exchange of ends scores one run. 

There are several variations as to how long a game of cricket can last. In professional cricket this can be anything from a match limited to 20 overs per side to a game played over 5 days. Depending on the length of the game being played, there are different rules that govern how a game is won, lost, drawn or tied. Cricket is essentially an outdoor sport, certainly at major level, and some games are played under floodlights. For example, it is played during the summer in the United Kingdom, Australia, New Zealand and South Africa, while in the West Indies, India, Pakistan, Sri Lanka and Bangladesh it is played mostly during the winter after the monsoon season.

Governance rests primarily with the International Cricket Council (ICC), based in Dubai, which organises the sport worldwide via the domestic controlling bodies of the member countries. The ICC administers both men's and women's cricket, both versions being played at international level. Although men cannot play women's cricket, the rules do not disqualify women from playing in a men's team.The rules are in the form of a code known as The Laws of Cricket [5] and these are maintained by the Marylebone Cricket Club (MCC), based in London, in consultation with the ICC and the domestic boards of control.

Plastic

Plastic is the general common term for a wide range of synthetic or semisynthetic organic solid materials suitable for the manufacture of industrial products. Plastics are typically polymers of high molecular weight, and may contain other substances to improve performance and/or reduce costs. The word derives from the Greek πλαστικός (plastikos), "fit for molding", from πλαστός (plastos) "molded" [1] [2]. It refers to their malleability, or plasticity during manufacture, that allows them to be cast, pressed, or extruded into an enormous variety of shapes—such as films, fibers, plates, tubes, bottles, boxes, and much more.

The common word "plastic" should not be confused with the technical adjective "plastic", which is applied to any material which undergoes a permanent change of shape (a "plastic deformation") when strained beyond a certain point. Aluminum, for instance, is "plastic" in this sense, but not "a plastic" in the common sense; while some plastics, in their finished forms, will break before deforming — and therefore are not "plastic" in the technical sense. Plastics can be classified by their chemical structure, namely the molecular units that make up the polymer's backbone and side chains. Some important groups in these classifications are the acrylics, polyesters, silicones, polyurethanes, and halogenated plastics. Plastics can also be classified by the chemical process used in their synthesis, e.g. as condensation, polyaddition, cross-linking, etc.[3]

Other classifications are based on qualities that are relevant for manufacturing or product design. Examples of such classes are the thermoplastic and thermoset, elastomer, structural, biodegradable, electrically conductive, etc. containers that is made of plastic can also be used as water containers. Due to their relatively low cost, ease of manufacture, versatility, and imperviousness to water, plastics are used in an enormous and expanding range of products, from paper clips to spaceships. They have already displaced many traditional materials—such as wood, stone, horn and bone, leather, paper, metal, glass and ceramic—in most of their former uses.

The use of plastics is constrained chiefly by their organic chemistry, which seriously limits their hardness, density, and their ability to resist heat, organic solvents, oxidation, and ionizing radiation. In particular, most plastics will melt or decompose when heated to a few hundred celsius. While plastics can be made electrically conductive to some extent, they are still no match for metals like copper or aluminum. Plastics are still too expensive to replace wood, concrete and ceramic in bulky items like ordinary buildings, bridges, dams, pavement, railroad ties, etc.

Factory

A factory (previously manufactory) or manufacturing plant is an industrial building where workers manufacture goods or supervise machines processing one product into another. Most modern factories have large warehouses or warehouse-like facilities that contain heavy equipment used for assembly line production. Archetypally, factories gather and concentrate resources — workers, capital and plant.

Many [1] believed that ancient China had been the first to create factories. In ancient China, imperial and private workshops, mills, and small manufactories had been employed since the Eastern Zhou Dynasty (771-221 BC), as noted in the historical text of the Zhou Li.[2] During the medieval Song Dynasty (960-1279 AD), independent and government sponsored industries were developed to meet the needs of a growing population that had reached over 100 million. For example, for the printing of paper money alone, the Song court established several government-run factories in the cities of Huizhou, Chengdu, Hangzhou, and Anqi.[3] 

The size of the workforce employed in these paper money factories were quite large, as it was recorded in 1175 AD that the factory at Hangzhou alone employed more than a thousand workers a day.[3] The Chinese iron industry was also expanded during the Song Dynasty, with a sixfold increase in per capita cast iron output between the years 806 and 1078 AD, meaning an overall weight of 127,000,000 kg (125,000 t) of cast iron product from state-run facilities was forged in the latter year alone.[4]

The first industrial complex for glass and pottery production was built in Ar-Raqqah, Syria, in the 8th century. Extensive experimentation was carried out at the complex, which was two kilometres in length, and a variety of innovative high-purity glass were developed there. Two other similar complexes have also been discovered, and nearly three hundred new chemical recipes for glass are known to have been produced at all three sites.[5] The first glass factories were thus built by Muslim craftsmen in the medieval Islamic world. The first glass factories in Europe were later built in the 11th century by Egyptian craftsmen in Corinth, Greece.[6]

Powder

A powder is a dry, bulk solid composed of a large number of very fine particles that may flow freely when shaken or tilted. Powders are a special sub-class of granular materials, although the terms powder and granular are sometimes used to distinguish separate classes of material. In particular, powders refer to those granular materials that have the finer grain sizes, and that therefore have a greater tendency to form clumps when flowing. Granulars refers to the coarser granular materials that do not tend to form clumps except when wet.

Typically, a powder can be compacted or loosened into a vastly larger range of bulk densities than can a coarser granular material. When deposited by sprinkling, a powder may be very light and fluffy. When vibrated or compressed it may become very dense and even lose its ability to flow. The bulk density of coarse sand, on the other hand, does not vary over an appreciable range. The clumping behavior of a powder arises because of the molecular Van der Waals force that causes individual grains to cling to one another. Actually, this force is present not just in powders, but in sand and gravel, too. However, in such coarse granular materials the weight and the inertia of the individual grains are much larger than the very weak Van der Waals forces, and therefore the tiny clinging between grains does not have a dominant effect on the bulk behavior of the material. Only when the grains are very small and lightweight does the Van der Waals force become predominant, causing the material clump like a powder.

Many other powder behaviors are common to all granular materials. These include segregation, stratification, jamming and unjamming, fragility, loss of kinetic energy, frictional shearing, compaction and Reynolds' dilatancy. Powders are transported in the atmosphere differently than a coarse granular material. For one thing, tiny particles have relatively little inertia compared to the drag force of the gas that surrounds them, and so they tend to go with the flow instead of traveling in straight lines. For this reason, powders may be an inhalation hazard. 

Larger particles cannot weave through the body's defenses in the nose and sinus, but will strike and stick to the mucous membranes. The body then moves the mucous out of the body to expel the particles. The smaller particles on the other hand can travel all the way to the lungs from which they cannot be expelled. Serious and sometimes fatal diseases such as silicosis are a result from working with certain powders without adequate respiratory protection.

Cosmetics

Cosmetics pronunciation: cosmetic (help•info)) are substances used to enhance or protect the appearance or odor of the human body. Cosmetics include skin-care creams, lotions, powders, perfumes, lipsticks, fingernail and toe nail polish, eye and facial makeup, permanent waves, colored contact lenses, hair colors, hair sprays and gels, deodorants, baby products, bath oils, bubble baths, bath salts, butters and many other types of products. Their use is widespread, especially among women in Western countries. A subset of cosmetics is called "make-up," which refers primarily to colored products intended to alter the user’s appearance. Many manufacturers distinguish between decorative cosmetics and care cosmetics.

The manufacture of cosmetics is currently dominated by a small number of multinational corporations that originated in the early 20th century, but the distribution and sale of cosmetics is spread among a wide range of different businesses. The U.S. Food and Drug Administration (FDA) which regulates cosmetics in the United States[1] defines cosmetics as: "intended to be applied to the human body for cleansing, beautifying, promoting attractiveness, or altering the appearance without affecting the body's structure or functions." This broad definition includes, as well, any material intended for use as a component of a cosmetic product. The FDA specifically excludes soap from this category

The first archaeological evidence of cosmetics usage is found in Egypt around 3500 BC.[citation needed] The Ancient Greeks and Romans also used cosmetics. The Romans and Ancient Egyptians used cosmetics containing poisonous mercury and often lead. The ancient kingdom of Israel was influenced by cosmetics as recorded in the Old Testament—2 Kings 9:30 where Jezebel painted her eyes—approximately 840 BC. The Biblical book of Esther describes various beauty treatments as well. In the western world, the advent of cosmetics was in the middle ages, although typically restricted to use within the upper classes.

Cosmetic use was frowned upon at some points in Western history. For example, in the 1800s, make-up was used primarily by prostitutes, and Queen Victoria publicly declared makeup improper, vulgar, and acceptable only for use by actors.[3] Adolf Hitler told women that face painting was for clowns and not for the women of the Master Race.[citation needed] Cosmetics have been in use for thousands of years. The absence of regulation of the manufacture and use of cosmetics has led to negative side effects, deformities, blindness, and even death through the ages. Examples of this were the prevalent use of ceruse(white lead), to cover the face during the Renaissance, and blindness caused by the mascara Lash Lure during the early 1900s.

Soap

Soap is an anionic surfactant used in conjunction with water for washing and cleaning that historically comes in solid bars but also in the form of a thick liquid. Soap, consisting of sodium (soda ash) or potassium (potash) salts of fatty acids is obtained by reacting fat with lye in a process known as saponification. The fats are hydrolyzed by the base, yielding alkali salts of fatty acids (crude soap) and glycerol.

Many cleaning agents today are technically not soaps, but detergents, which are less expensive and easier to manufacture. Soaps are useful for cleaning because soap molecules attach readily to both nonpolar molecules (such as grease or oil) and polar molecules (such as water). Although grease will normally adhere to skin or clothing, the soap molecules can attach to it as a "handle" and make it easier to rinse away. Applied to a soiled surface, soapy water effectively holds particles in suspension so the whole of it can be rinsed off with clean water.

The hydrocarbon ("fatty") portion dissolves dirt and oils, while the ionic end makes it soluble in water. Therefore, it allows water to remove normally-insoluble matter by emulsification The most popular soapmaking process today is the cold process method, where fats such as olive oil react with lye. Soapmakers sometimes use the melt and pour process, where a premade soap base is melted and poured in individual molds. While some people think that this is not really soap-making, the Hand Crafted Soap Makers Guild considers it a form of soap making or soap crafting. Some soapers also practice other processes, such as the historical hot process, and make special soaps such as clear soap (glycerin soap), which must be made through the melt-and-pour process.

Handmade soap differs from industrial soap in that, usually, an excess of fat is sometimes used to consume the alkali (superfatting), and in that the glycerin is not removed leaving a naturally moisturising soap and not pure detergent. Superfatted soap, soap which contains excess fat, is more skin-friendly than industrial soap. However, if not properly formulated, superfatted soaps can leave users with a "greasy" feel to their skin. Often, emollients such as jojoba oil or shea butter are added 'at trace' (the point at which the saponification process is sufficiently advanced that the soap has begun to thicken), after most of the oils have saponified, so that they remain unreacted in the finished soap. Superfatting can also be accomplished through a process called superfat discount, where, instead of putting in extra fats, the soap maker puts in less lye.

Insurance

Insurance, in law and economics, is a form of risk management primarily used to hedge against the risk of a contingent loss. Insurance is defined as the equitable transfer of the risk of a loss, from one entity to another, in exchange for a premium, and can be thought of as a guaranteed small loss to prevent a large, possibly devastating loss. An insurer is a company selling the insurance; an insured is the person or entity buying the insurance. The insurance rate is a factor used to determine the amount, called the premium, to be charged for a certain amount of insurance coverage. Risk management, the practice of appraising and controlling risk, has evolved as a discrete field of study and practice.

A large number of homogeneous exposure units. The vast majority of insurance policies are provided for individual members of very large classes. Automobile insurance, for example, covered about 175 million automobiles in the United States in 2004.[2] The existence of a large number of homogeneous exposure units allows insurers to benefit from the so-called “law of large numbers,” which in effect states that as the number of exposure units increases, the actual results are increasingly likely to become close to expected results. There are exceptions to this criterion. Lloyd's of London is famous for insuring the life or health of actors, actresses and sports figures. Satellite Launch insurance covers events that are infrequent. Large commercial property policies may insure exceptional properties for which there are no ‘homogeneous’ exposure units.

Definite Loss. The event that gives rise to the loss that is subject to insurance should, at least in principle, take place at a known time, in a known place, and from a known cause. The classic example is death of an insured person on a life insurance policy. Fire, automobile accidents, and worker injuries may all easily meet this criterion. Other types of losses may only be definite in theory and cause of a loss should be clear enough that a reasonable person, with sufficient information, could objectively verify all three elements.

Accidental Loss. The event that constitutes the trigger of a claim should be fortuitous, or at least outside the control of the beneficiary of the insurance. The loss should be ‘pure,’ in the sense that it results from an event for which there is only the opportunity for cost. Events that contain speculative elements, such as ordinary business risks, are generally not considered insurable. Large Loss. The size of the loss must be meaningful from the perspective of the insured. Insurance premiums need to cover both the expected cost of losses, plus the cost of issuing and administering the policy, adjusting losses, and supplying the capital needed to reasonably assure that the insurer will be able to pay claims.

Health care

Health care, or healthcare, is the prevention, treatment, and management of illness, and the preservation of health through services offered by the medical, dental, nursing, and allied health professions. Health care embraces all the goods and services designed to promote health, including “preventive, curative and palliative interventions, whether directed to individuals or to populations”.[1] The organised provision of such services may constitute a health care system. This can include specific governmental organizations such as, in the UK, the National Health Service or a cooperation across the National Health Service and Social Services as in Shared Care. Before the term health care became popular, English-speakers referred to medicine or to the health sector and spoke of the treatment and prevention of illness and disease.

In most developed countries and many developing countries health care is provided to everyone regardless of their ability to pay. The National Health Service, established in 1948 by Clement Atlee's Labour government in the United Kingdom, was the world's first universal health care system provided by government and paid for from general taxation. Alternatively, compulsory government funded health insurance with nominal fees can be provided, as in Italy. Universal health care contrasts to the systems like health care in the United States or South Africa, though South Africa is one of the many countries attempting health care reform.[2] The United States is the only wealthy, industrialized nation that does not provide universal health care.

The health care industry is considered an industry or profession which includes peoples' exercise of skill or judgment or the providing of a service related to the preservation or improvement of the health of individuals or the treatment or care of individuals who are injured, sick, disabled, or infirm. The delivery of modern health care depends on an expanding group of trained professionals coming together as an interdisciplinary team.[5][6]

Consuming over 10 percent of gross domestic product of most developed nations, health care can form an enormous part of a country's economy. In 2003, health care costs paid to hospitals, physicians, nursing homes, diagnostic laboratories, pharmacies, medical device manufacturers and other components of the health care system, consumed 16.3 percent[7] of the GDP of the United States, the largest of any country in the world. For the United States, the health share of gross domestic product (GDP) is expected to hold steady in 2006 before resuming its historical upward trend, reaching 19.5 percent of GDP by 2016.[8] In 2001, for the OECD countries the average was 8.4 percent[9] with the United States (13.9%), Switzerland (10.9%), and Germany (10.7%) being the top three.

Welfare

Welfare is financial assistance paid to people by governments. Some welfare is general, while specific and can only be invoked under certain circumstances, such as a scholarship. Welfare payments can be made to individuals or to companies or entities--these latter payments are often considered corporate welfare. Individuals may apply for welfare due to disability, lack of education or job training, a low demand for unskilled labor, substance abuse, or other reasons. Assistance may also take the form of other relief, such as tax credits for working mothers.

Welfare is known by a variety of names in different countries, all with the avowed purpose of providing an economic or social safety net for somehow disadvantaged members of society. Almost all developed nations provide some kind of safety net of this kind; nations where such programs are especially prominent are known as welfare states. The desired outcome and purpose of welfare varies. For welfare for the non-disabled, the purpose often is to prevent complete destitution. Welfare or assistance for the disabled, in contrast, does not eventually expect non-dependency, and the justification is more philosophical.

"Corporate welfare," usually in the form of favorable tax policy, is sometimes used in order to provide capital to an industry that the government perceives needs financial assistance in order to survive or to expand, or which the government wishes to support for political or economic purposes. Some of these ideal outcomes and purposes, as well as welfare's effectiveness have been challenged by political groups, such as those who oppose big government and "forced charity", such as minarchists or libertarians.

The amounts paid to recipients are typically modest, and may fall below the poverty line. Recipients must usually demonstrate a low level of income such as by way of "means testing", or financial hardship, or that they satisfy some other requirement such as childcare responsibilities or disability. Those receiving unemployment benefits may also have to regularly demonstrate that they are periodically searching for employment. Some countries assign specific jobs to recipients who must work in these roles in order for welfare payments to continue. In the United States and Canada, such programs are known as workfare.

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are often used, such as based on similarity of DNA or morphology. Presence of specific locally adapted traits may further subdivide species into subspecies.

The commonly used names for plant and animal taxa sometimes correspond to species: for example, "lion," "walrus," and "Camphor tree" – each refers to a species. In other cases common names do not: for example, "deer" refers to a family of 34 species, including Eld's Deer, Red Deer and Elk (Wapiti). The last two species were once considered a single species, illustrating how species boundaries may change with increased scientific knowledge.

Each species is placed within a single genus. This is a hypothesis that the species is more closely related to other species within its genus than to species of other genera. All species are given a binomial name consisting of the generic name and specific name (or specific epithet). For example, Pinus palustris (commonly known as the Longleaf Pine). The taxonomic ranks are life, domain, kingdom, phylum, class, order, family, genus, and species. A usable definition of the word "species" and reliable methods of identifying particular species are essential for stating and testing biological theories and for measuring biodiversity. Traditionally, multiple examples of a proposed species must be studied for unifying characters before it can be regarded as a species. Extinct species known only from fossils are generally difficult to give precise taxonomic rankings to.

Because of the difficulties with both defining and tallying the total numbers of different species in the world, it is estimated that there are anywhere between 2 and 100 million different species.[1] In scientific classification, a species is assigned a two-part name, treated as Latin, although roots from any language can be used as well as names of locales or individuals. The genus is listed first (with its leading letter capitalized), followed by a second term: for example, gray wolves belong to the species Canis lupus, coyotes to Canis latrans, golden jackals to Canis aureus, etc., and all of those belong to the genus Canis (which also contains many other species). The name of the species is the whole binomial, not just the second term (which may be called specific name for animals).

Environmental disaster

An environmental disaster is a disaster that is due to human activity and should not be confused with natural disasters. In this case, the impact of humans' alteration of the ecosystem has led to widespread and/or long-lasting consequences. It can include the deaths of animals (including humans) and plant systems, or severe disruption of human life, possibly requiring migration. Some might view, for example, the Three Gorges Dam as an environmental disaster, requiring the migration of 1 million people. Others might see it as beneficial to stop flooding.

Some might see the destruction of most of the North American forests as beneficial, as it cleared land for farming and other uses. In Ireland, the clearing of forest led to the formation of bogs, which some people like for their beauty, as well as their products such as peat moss. Others might see this deforestation as negative.

More cynical examples would be, for example, that Saddam Hussein felt it was beneficial to get rid of the Madan people by draining the Al-Hawizeh marsh, because they had joined the United States in the first Gulf War. Another example is the depopulation of the American Bison. It was thought by General William Sherman and others to be a good way to get rid of the American Indians living in the Great Plains, and would make way for the exploding population of the United States of America to take over the area.

The pulverization of the Twin Towers with the Collapse of the World Trade Center and the release of Ground Zero dust propelled fine toxic dust into the vicinity; some have challenged whether this was an industrial disaster since this was a commercial site.

Volcano

A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot, molten rock, ash, and gases to escape from below the surface. Volcanic activity involving the extrusion of rock tends to form mountains or features like mountains over a period of time. Volcanoes are generally found where tectonic plates are diverging or converging. A mid-oceanic ridge, for example the Mid-Atlantic Ridge, has examples of volcanoes caused by "divergent tectonic plates" pulling apart; the Pacific Ring of Fire has examples of volcanoes caused by "convergent tectonic plates" coming together. By contrast, volcanoes are usually not created where two tectonic plates slide past one another. Volcanoes can also form where there is stretching and thinning of the Earth's crust (called "non-hotspot intraplate volcanism"), such as in the African Rift Valley, the Wells Gray-Clearwater volcanic field and the Rio Grande Rift in North America and the European Rhine Graben with its Eifel volcanoes.

Volcanoes can be caused by "mantle plumes". These so-called "hotspots" , for example at Hawaii, can occur far from plate boundaries. Hotspot volcanoes are also found elsewhere in the solar system, especially on rocky planets and moons. At the mid-oceanic ridges, two tectonic plates diverge from one another. New oceanic crust is being formed by hot molten rock slowly cooling and solidifying. The crust is very thin at mid-oceanic ridges due to the pull of the tectonic plates.

Subduction zones are places where two plates, usually an oceanic plate and a continental plate, collide. In this case, the oceanic plate subducts, or submerges under the continental plate forming a deep ocean trench just offshore. Water released from the subducting plate lowers the melting temperature of the overlying mantle wedge, creating magma. This magma tends to be very viscous due to its high silica content, so often does not reach the surface and cools at depth. When it does reach the surface, a volcano is formed. Typical examples for this kind of volcano are Mount Etna and the volcanoes in the Pacific Ring of Fire.

Hotspots are not usually located on the ridges of tectonic plates, but above mantle plumes, where the convection of the Earth's mantle creates a column of hot material that rises until it reaches the crust, which tends to be thinner than in other areas of the Earth. The temperature of the plume causes the crust to melt and form pipes, which can vent magma. Because the tectonic plates move whereas the mantle plume remains in the same place, each volcano becomes dormant after a while and a new volcano is then formed as the plate shifts over the hotspot. The Hawaiian Islands are thought to be formed in such a manner, as well as the Snake River Plain, with the Yellowstone Caldera being the part of the North American plate currently above the hotspot.

Cyclone

In meteorology, a cyclone refers to an area of closed, circular fluid motion rotating in the same direction as the Earth[1][2]. This is usually characterized by inward spiraling winds that rotate counter clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere of the Earth. Large-scale cyclonic circulations are almost always centred on areas of low atmospheric pressure[3][4]. The largest low-pressure systems are cold-core polar cyclones and extratropical cyclones which lie on the synoptic scale. Warm-core cyclones such as tropical cyclones, mesocyclones, and polar lows lie within the smaller mesoscale. Subtropical cyclones are of intermediate size.[5][6] Cyclones have also been seen on other planets outside of the Earth, such as Mars and Neptune.[7][8]

Cyclogenesis describes the process of cyclone formation and intensification [9]. Extratropical cyclones form as waves in large regions of enhanced midlatitude temperature contrasts called baroclinic zones. These zones contract to form weather fronts as the cyclonic circulation closes and intensifies. Later in their life cycle, cyclones occlude as cold core systems. A cyclone's track is guided over the course of its 2 to 6 day life cycle by the steering flow of the polar or subtropical jetstream.

Weather fronts separate two masses of air of different densities and are associated with the most prominent meteorological phenomena. Air masses separated by a front may differ in temperature or humidity. Strong cold fronts typically feature narrow bands of thunderstorms and severe weather, and may on occasion be preceded by squall lines or dry lines. They form west of the circulation center and generally move from west to east. Warm fronts form east of the cyclone center and are usually preceded by stratiform precipitation and fog. They move poleward ahead of the cyclone path. Occluded fronts form late in the cyclone life cycle near the enter of the cyclone and often wrap around the storm center.

Tropical cyclogenesis describes the process of development of tropical cyclones. Tropical cyclones form due to latent heat driven by significant thunderstorm activity, and are warm core.[10] Cyclones can transition between extratropical, subtropical, and tropical phases under the right conditions. Mesocyclones form as warm core cyclones over land, and can lead to tornado formation.[11] Waterspouts can also form from mesocyclones, but more often develop from environments of high instability and low vertical wind shear.[12]

Waste management

Waste management is the collection, transport, processing, recycling or disposal of waste materials. The term usually relates to materials produced by human activity, and is generally undertaken to reduce their effect on health, the environment or aesthetics. Waste management is also carried out to recover resources from it. Waste management can involve solid, liquid, gaseous or radioactive substances, with different methods and fields of expertise for each.

Waste management practices differ for developed and developing nations, for urban and rural areas, and for residential and industrial, producers. Management for non-hazardous residential and institutional waste in metropolitan areas is usually the responsibility of local government authorities, while management for non-hazardous commercial and industrial waste is usually the responsibility of the generator. Waste management methods vary widely between areas for many reasons, including type of waste material, nearby land uses, and the area available.

Disposing of waste in a landfill involves burying waste to dispose of it, and this remains a common practice in most countries. Landfills were often established in abandoned or unused quarries, mining voids or borrow pits. A properly-designed and well-managed landfill can be a hygienic and relatively inexpensive method of disposing of waste materials. Older, poorly-designed or poorly-managed landfills can create a number of adverse environmental impacts such as wind-blown litter, attraction of vermin, and generation of liquid leachate. Another common byproduct of landfills is gas (mostly composed of methane and carbon dioxide), which is produced as organic waste breaks down anaerobically. This gas can create odor problems, kill surface vegetation, and is a greenhouse gas.

Design characteristics of a modern landfill include methods to contain leachate such as clay or plastic lining material. Deposited waste is normally compacted to increase its density and stability, and covered to prevent attracting vermin (such as mice or rats). Many landfills also have landfill gas extraction systems installed to extract the landfill gas. Gas is pumped out of the landfill using perforated pipes and flared off or burnt in a gas engine to generate electricity.

Finance

The field of finance refers to the concepts of time, money and risk and how they are interrelated. Banks are the main facilitators of funding through the provision of credit, although private equity, mutual funds, hedge funds, and other organizations have become important. Financial assets, known as investments, are financially managed with careful attention to financial risk management to control financial risk. Financial instruments allow many forms of securitized assets to be traded on securities exchanges such as stock exchanges, including debt such as bonds as well as equity in publicly-traded corporations.

An entity whose income exceeds its expenditure can lend or invest the excess income. On the other hand, an entity whose income is less than its expenditure can raise capital by borrowing or selling equity claims, decreasing its expenses, or increasing its income. The lender can find a borrower, a financial intermediary such as a bank, or buy notes or bonds in the bond market. The lender receives interest, the borrower pays a higher interest than the lender receives, and the financial intermediary pockets the difference.

A bank aggregates the activities of many borrowers and lenders. A bank accepts deposits from lenders, on which it pays the interest. The bank then lends these deposits to borrowers. Banks allow borrowers and lenders, of different sizes, to coordinate their activity. Banks are thus compensators of money flows in space. A specific example of corporate finance is the sale of stock by a company to institutional investors like investment banks, who in turn generally sell it to the public. The stock gives whoever owns it part ownership in that company. If you buy one share of XYZ Inc, and they have 100 shares outstanding (held by investors), you are 1/100 owner of that company. Of course, in return for the stock, the company receives cash, which it uses to expand its business; this process is known as "equity financing". Equity financing mixed with the sale of bonds (or any other debt financing) is called the company's capital structure.

Finance is used by individuals (personal finance), by governments (public finance), by businesses (corporate finance), as well as by a wide variety of organizations including schools and non-profit organizations. In general, the goals of each of the above activities are achieved through the use of appropriate financial instruments, with consideration to their institutional setting. Finance is one of the most important aspects of business management. Without proper financial planning a new enterprise is unlikely to be successful. Managing money (a liquid asset) is essential to ensure a secure future, both for the individual and an organization.

Desert

A desert is a landscape or region that receives very little precipitation. Deserts can be defined as areas that receive an average annual precipitation of less than 250 mm (10 in),[1][2] or as areas in which more water is lost than falls as precipitation.[3] In the Köppen climate classification system, deserts are classed as BWh (hot desert) or BWk (temperate desert). In the Thornthwaite climate classification system, deserts would be classified as arid megathermal climates.

Deserts are part of a wider classification of regions that, on an average annual basis, have a moisture deficit (i.e. they can potentially lose more than is received). Deserts are located where vegetation cover is sparse to almost nonexistent Deserts take up about one third of the Earth's land surface.[1] Hot deserts usually have a large diurnal and seasonal temperature range, with high daytime temperatures, and low nighttime temperatures (due to extremely low humidity). In hot deserts the temperature in the daytime can reach 45 °C/113 °F or higher in the summer, and dip to 0 °C/32°F or lower in the winter. Water acts to trap infrared radiation from both the sun and the ground, and dry desert air is incapable of blocking sunlight during the day or trapping heat during the night. Thus, during daylight most of the sun's heat reaches the ground, and as soon as the sun sets the desert cools quickly by radiating its heat into space. Urban areas in deserts lack large (more than 14 °C/25 °F) daily temperature variations, partially due to the urban heat island effect.

Many deserts are formed by rain shadows; mountains blocking the path of precipitation to the desert. Deserts are often composed of sand and rocky surfaces. Sand dunes called ergs and stony surfaces called hamada surfaces compose a minority of desert surfaces. Exposures of rocky terrain are typical, and reflect minimal soil development and sparseness of vegetation
Bottomlands may be salt-covered flats.

Eolian processes are major factors in shaping desert landscapes. Cold deserts (also known as polar deserts) have similar features, except the main form of precipitation is snow rather than rain. Antarctica is the world's largest cold desert (composed of about 98 percent thick continental ice sheet and 2 percent barren rock). Some of the barren rock is to be found in the so-called Dry Valleys of Antarctica that almost never get snow, which can have ice-encrusted saline lakes that suggest evaporation far greater than the rare snowfall due to the strong katabatic winds that evaporate even ice.

Island

An island (IPA: /ˈaɪlənd/) or isle (/ˈaɪl/) is any piece of land that is completely surrounded by water in two dimensions, above high tide, and isolated from other significant landmasses. Very small islands such as emergent land features on atolls are called islets. A key or cay is another name for a small island or islet. An island in a river or lake may be called an eyot, /ˈaɪət/. There are two main types of islands: continental islands and oceanic islands. There are also artificial islands. A grouping of geographically and/or geologically related islands is called an archipelago.

The word island comes from Old English ī(e)gland (literally, "watery land"). However, the spelling of the word was modified in the 15th century by association with the etymologically unrelated Old French loanword isle.[1] There is no standard of size which distinguishes islands from islets and continents.

When defining islands as pieces of land that are completely surrounded by water, narrow bodies of water like rivers and canals are generally left out of consideration[citation needed]. For instance, in France the Canal du Midi connects the Garonne river to the Mediterranean Sea, thereby completing a continuous water connection from the Atlantic Ocean to the Mediterranean Sea. So technically, the land mass that includes the Iberian Peninsula and the part of France that is south of the Garonne River and the Canal du Midi is completely surrounded by water. For a completely natural example, the Orinoco River splits into two branches near Tamatama, in Amazonas state, Venezuela. The southern branch flows south and joins the Rio Negro, and then the Amazon. Thus, all of the Guianas (Guyana, Suriname, and French Guiana) and substantial parts of Brazil and Venezuela are surrounded by (river or ocean) water. These instances are not generally considered islands.

This also helps explain why Africa-Eurasia can be seen as one continuous landmass (and thus technically the biggest island): generally the Suez Canal is not seen as something that divides the land mass in two. Australia is often considered the largest island because it is covered on all sides by water while not being connected to another body of land. On the other hand, an island may still be described as such despite the presence of a land bridge, e.g., Singapore and its causeway or the various Dutch delta Islands, such as IJsselmonde. The retaining of the island description may therefore be to some degree simply due to historical reasons - though the land bridges are often of a different geological nature (for example sand instead of stone), and thus the islands remain islands in a more scientific sense as well.

Flood

A flood is an overflow of an expanse of water that submerges land, a deluge.[1] In the sense of "flowing water", the word may also be applied to the inflow of the tide. Flooding may result from the volume of water within a body of water, such as a river or lake, which overflows, with the result that some of the water escapes its normal boundaries.[2] While the size of a lake or other body of water will vary with seasonal changes in precipitation and snow melt, it is not a significant flood unless such escapes of water endangers land areas used by man like a village, city or other inhabited area.

Floods can also occur in rivers, when the strength of the river is so high it flows out of the river channel, particularly at bends or meanders and cause damage to homes and businesses along such rivers. While flood damage can be virtually eliminated by moving away from rivers and other bodies of water, since time out of mind, man has lived and worked by the water to seek sustenance and capitalize on the gains of cheap and easy travel and commerce by being near water. That humans continue to inhabit areas threatened by flood damage is only evidence that the value of being near the water far exceeds the costs of repeated periodic flooding.

The word comes from the Old English flod, a word common to Teutonic languages (compare German Flut, Dutch vloed from the same root as is seen in flow, float). The term "The Flood," capitalized, usually refers to the great Universal School described in the Bible, in Genesis, and is treated at Deluge. In many countries across the world, rivers prone to floods are often carefully managed. Defences such as levees,[5] bunds, reservoirs, and weirs are used to prevent rivers from bursting their banks. Coastal flooding has been addressed in Europe and the Americas with coastal defences, such as sea walls, beach nourishment, and barrier islands.

There are many disruptive effects of flooding on human settlements and economic activities. However, flooding can bring benefits, such as making soil more fertile and providing nutrients in which it is deficient. Periodic flooding was essential to the well-being of ancient communities along the Tigris-Euphrates Rivers, the Nile River, the Indus River, the Ganges and the Yellow River, among others. The viability for hydrological based renewable sources of energy is higher in flood prone regions.

Earthquake

An earthquake (also known as a tremor or temblor) is the result of a sudden release of energy in the Earth's crust that creates seismic waves. Earthquakes are recorded with a seismometer, also known as a seismograph. The moment magnitude of an earthquake is conventionally reported, or the related and mostly obsolete Richter magnitude, with magnitude 3 or lower earthquakes being mostly imperceptible and magnitude 7 causing serious damage over large areas. Intensity of shaking is measured on the modified Mercalli scale.

At the Earth's surface, earthquakes manifest themselves by shaking and sometimes displacing the ground. When a large earthquake epicenter is located offshore, the seabed sometimes suffers sufficient displacement to cause a tsunami. The shaking in earthquakes can also trigger landslides and occasionally volcanic activity. In its most generic sense, the word earthquake is used to describe any seismic event—whether a natural phenomenon or an event caused by humans—that generates seismic waves. Earthquakes are caused mostly by rupture of geological faults, but also by volcanic activity, landslides, mine blasts, and nuclear experiments. An earthquake's point of initial rupture is called its focus or hypocenter. The term epicenter refers to the point at ground level directly above this.

Tectonic earthquakes will occur anywhere within the earth where there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane. In the case of transform or convergent type plate boundaries, which form the largest fault surfaces on earth, they will move past each other smoothly and aseismically only if there are no irregularities or asperities along the boundary that increase the frictional resistance. Most boundaries do have such asperities and this leads to a form of stick-slip behaviour. Once the boundary has locked, continued relative motion between the plates leads to increasing stress and therefore, stored strain energy in the volume around the fault surface. This continues until the stress has risen sufficiently to break through the asperity, suddenly allowing sliding over the locked portion of the fault, releasing the stored energy.

This energy is released as a combination of radiated elastic strain seismic waves, frictional heating of the fault surface, and cracking of the rock, thus causing an earthquake. This process of gradual build-up of strain and stress punctuated by occasional sudden earthquake failure is referred to as the Elastic-rebound theory. It is estimated that only 10 percent or less of an earthquake's total energy is radiated as seismic energy. Most of the earthquake's energy is used to power the earthquake fracture growth or is converted into heat generated by friction.

Metric Spcae

In mathematics, a metric space is a set where a notion of distance (called a metric) between elements of the set is defined. The metric space which most closely corresponds to our intuitive understanding of space is the 3-dimensional Euclidean space. In fact, the notion of "metric" is a generalization of the Euclidean metric arising from the four long known properties of the Euclidean distance. The Euclidean metric defines the distance between two points as the length of the straight line connecting them.

The geometric properties of the space depends on the metric chosen, and by using a different metric we can construct interesting non-Euclidean geometries such as those used in the theory of general relativity. A metric space also induces topological properties like open and closed sets which leads to the study of even more abstract topological spaces.

A metric space M is called bounded if there exists some number r, such that d(x,y) ≤ r for all x and y in M. The smallest possible such r is called the diameter of M. The space M is called precompact or totally bounded if for every r > 0 there exist finitely many open balls of radius r whose union covers M. Since the set of the centres of these balls is finite, it has finite diameter, from which it follows (using the triangle inequality) that every totally bounded space is bounded. The converse does not hold, since any infinite set can be given the discrete metric (one of the examples above) under which it is bounded and yet not totally bounded.

Note that in the context of intervals in the space of real numbers and occasionally regions in a Euclidean space Rn a bounded set is referred to as "a finite interval" or "finite region". However boundedness should not in general be confused with "finite", which refers to the number of elements, not to how far the set extends; finiteness implies boundedness, but not conversely.

Solar Energy

Solar energy is the light and radiant heat from the Sun that drives the Earth's climate, plant, marine and terrestrial life and cycles. Humans have tried since ancient times to harness solar energy using a range of ever-evolving technologies. From cultivating food using the seasonal cycles to using direct sunlight to dry food for storage to the use of photovoltaic cells to generate electricity and now giant mirrors to generate concentrated radiant heat, has been a non-stop quest to capture this practically unlimited source. Solar energy is also a perishable commodity. Direct solar energy is neither geographically nor temporally available at points of use in adequate quantities.

Solar radiation, along with secondary solar resources such as wind and tidal power or wave power, gravity driven river flows and biomass, accounts for most of the available renewable energy on Earth. Once this energy is captured in the form of heat or electricity, it is like any other energy source and can be put to all the uses that human ingenuity can devise. Of all the renewable energy resources only bio-mass, once created, is a natural storehouse of energy. This is a property it shares with fossil fuels. Most of the cost and operational problems associated with alternative energy sources arise from the fact that once the energy is converted to heat or electricity, it has to be used right away or stored at enormous cost and trouble. Even for hydro-electricity, the water has to be stored using barriers built at enormous cost and risk. Also the timing cycles of the water needs of down-stream farmers often clash with the power needs of the rest.

The Earth receives 174 petawatts (PW) of incoming solar radiation (insolation) at the upper atmosphere.[1] Approximately 30% is reflected back to space while the rest is absorbed by clouds, oceans and land masses. The spectrum of solar light at the Earth's surface is mostly spread across the visible and near-infrared ranges with a small part in the near-ultraviolet.[2] The absorbed solar light heats the land surface, oceans and atmosphere. The warm air containing evaporated water from the oceans rises, driving atmospheric circulation or convection. When this air reaches a high altitude, where the temperature is low, water vapor condenses into clouds, which rain onto the earth's surface, completing the water cycle.

The latent heat of water condensation amplifies convection, producing atmospheric phenomena such as cyclones and anti-cyclones. Wind is a manifestation of the atmospheric circulation driven by solar energy.[3] Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14 °C.[4] The conversion of solar energy into chemical energy via photosynthesis produces food, wood and the biomass from which fossil fuels are derived

Energy Resources

In order to directly compare world energy resources and consumption of energy, this article uses SI units and prefixes and measures energy rate (or power) in watts (W) and amounts of energy in joules (J). One watt is one joule per second. In 2005, total worldwide energy consumption was 500 EJ (= 5 x 1020 J) with 86.5% derived from the combustion of fossil fuels, although there is at least 10% uncertainty in that figure.[1] This is equivalent to an average energy consumption rate of 16 TW (= 1.6 x 1013 W). Not all of the world's economies track their energy consumption with the same rigor, and the exact energy content of a barrel of oil or a ton of coal will vary with quality.

Most of the world's energy resources are from the sun's rays hitting earth - some of that energy has been preserved as fossil energy, some is directly or indirectly usable e.g. via wind, hydro or wave power. The term solar constant is the amount of incoming solar electromagnetic radiation per unit area, measured on the outer surface of Earth's atmosphere, in a plane perpendicular to the rays. The solar constant includes all types of solar radiation, not just visible light. It is measured by satellite to be roughly 1366 watts per square meter, though it fluctuates by about 6.9% during a year - from 1412 W/m2 in early January to 1321 W/m2 in early July, due to the earth's varying distance from the sun, and by a few parts per thousand from day to day. For the whole Earth, with a cross section of 127,400,000 km², the total energy rate is 1.740×1017 W, plus or minus 3.5%. This 174 PW is the total rate of solar energy received by the planet; about half, 89 PW, reaches the earth's surface.

The estimates of remaining worldwide energy resources vary, with the remaining fossil fuels totaling an estimated 0.4 YJ (1 YJ = 1024J) and the available nuclear fuel such as uranium exceeding 2.5 YJ. Fossil fuels range from 0.6-3 YJ if estimates of reserves of methane clathrates are accurate and become technically extractable. Mostly thanks to the Sun, the world also has a renewable usable energy flux that exceeds 120 PW (8,000 times 2004 total usage), or 3.8 YJ/yr

Coal fueled the industrial revolution in the 18th and 19th century. With the advent of the automobile, airplanes and the spreading use of electricity, oil became the dominant fuel during the twentieth century. The growth of oil as the largest fossil fuel was further enabled by steadily dropping prices from 1920 until 1973. After the oil shocks of 1973 and 1979, during which the price of oil increased from 5 to 45 US dollars per barrel, there was a shift away from oil.[12] Coal and nuclear became the fuels of choice for electricity generation and conservation measures increased energy efficiency. In the US the average car more than doubled the number of miles

Magnetism

In physics, magnetism is one of the phenomena by which materials exert attractive or repulsive forces on other materials. Some well-known materials that exhibit easily detectable magnetic properties (called magnets) are nickel, iron, cobalt, and their alloys; however, all materials are influenced to greater or lesser degree by the presence of a magnetic field. Aristotle attributes the first of what could be called a scientific discussion on magnetism to Thales, who lived from about 625 BC to about 545 BC.[1] Around the same time in ancient India, the Indian surgeon, Sushruta, was the first to make use of the magnet for surgical purposes.[2] In ancient China, the earliest literary reference to magnetism lies in a 4th century BC book called Book of the Devil Valley Master "The lodestone makes iron come or it attracts it."[3] The earliest mention of the attraction of a needle appears in a work composed between AD 20 and 100 (Louen-heng):

"A lodestone attracts a needle."[4] The ancient Chinese scientist Shen Kuo (1031-1095) was the first person to write of the magnetic needle compass and that it improved the accuracy of navigation by employing the astronomical concept of true north (Dream Pool Essays, AD 1088 ), and by the 12th century the Chinese were known to use the lodestone compass for navigation. Alexander Neckham, by 1187, was the first in Europe to describe the compass and its use for navigation. In 1269, Peter Peregrinus de Maricourt wrote the Epistola de magnete, the first extant treatise describing the properties of magnets. In 1282, the properties of magnets and the dry compass were discussed by Al-Ashraf, a Yemeni physicist, astronomer and geographer.[5]

In 1600, William Gilbert published his De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure (On the Magnet and Magnetic Bodies, and on the Great Magnet the Earth). In this work he describes many of his experiments with his model earth called the terrella. From his experiments, he concluded that the Earth was itself magnetic and that this was the reason compasses pointed north (previously, some believed that it was the pole star (Polaris) or a large magnetic island on the north pole that attracted the compass).

An understanding of the relationship between electricity and magnetism began in 1819 with work by Hans Christian Oersted, a professor at the University of Copenhagen, who discovered more or less by accident that an electric current could influence a compass needle. This landmark experiment is known as Oersted's Experiment. Several other experiments followed, with André-Marie Ampère, Carl Friedrich Gauss, Michael Faraday, and others finding further links between magnetism and electricity.

Electricity

Electricity (from the Greek word ηλεκτρον, (elektron), meaning amber, and finally from New Latin ēlectricus, "amber-like") is a general term that encompasses a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena such as lightning and static electricity, but in addition, less familiar concepts such as the electromagnetic field and electromagnetic induction.

In general usage, the word 'electricity' is adequate to refer to a number of physical effects. However, in scientific usage, the term is vague, and these related, but distinct, concepts are better identified by more precise terms: Electric charge – a property of some subatomic particles, which determines their electromagnetic interactions. Electrically charged matter is influenced by, and produces, electromagnetic fields. Electric current – a movement or flow of electrically charged particles, typically measured in amperes. Electric field – an influence produced by an electric charge on other charges in its vicinity. the capacity of an electric field to do work, typically measured in volts.

Electromagnetism – a fundamental interaction between the magnetic field and the presence and motion of an electric charge. Electrical phenomena have been studied since antiquity, though advances in the science were not made until the seventeenth and eighteenth centuries. Practical applications for electricity however remained few, and it would not be until the late nineteenth century that engineers were able to put it to industrial and residential use. The rapid expansion in electrical technology at this time transformed industry and society. Electricity's extraordinary versatility as a source of energy means it can be put to an almost limitless set of applications which include transport, heating, lighting, communications, and computation. The backbone of modern industrial society is, and for the foreseeable future can be expected to remain, the use of electrical power.

Long before any knowledge of electricity existed people were aware of shocks from electric fish. Ancient Egyptian texts dating from 2750 BC referred to these fish as the "Thunderer of the Nile", and described them as the "protectors" of all other fish. They were again reported millennia later by ancient Greek, Roman and Arabic naturalists and physicians.[2] Several ancient writers, such as Pliny the Elder and Scribonius Largus, attested to the numbing effect of electric shocks delivered by catfish and torpedo rays, and knew that such shocks could travel along conducting objects.[3] Patients suffering from ailments such as gout or headache were directed to touch electric fish in the hope that the powerful jolt might cure them.[4]

Superconductivity

Superconductivity is a phenomenon occurring in certain materials generally at very low temperatures, characterized by exactly zero electrical resistance and the exclusion of the interior magnetic field (the Meissner effect). The electrical resistivity of a metallic conductor decreases gradually as the temperature is lowered. However, in ordinary conductors such as copper and silver, impurities and other defects impose a lower limit. Even near absolute zero a real sample of copper shows a non-zero resistance. The resistance of a superconductor, despite these imperfections, drops abruptly to zero when the material is cooled below its "critical temperature".

An electric current flowing in a loop of superconducting wire can persist indefinitely with no power source. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum mechanical phenomenon. It cannot be understood simply as the idealization of "perfect conductivity" in classical physics. Superconductivity occurs in a wide variety of materials, including simple elements like tin and aluminium, various metallic alloys and some heavily-doped semiconductors. Superconductivity does not occur in noble metals like gold and silver, nor in pure samples of ferromagnetic metals.

In 1986 the discovery of a family of cuprate-perovskite ceramic materials known as high-temperature superconductors, with critical temperatures in excess of 90 kelvins, spurred renewed interest and research in superconductivity for several reasons. As a topic of pure research, these materials represented a new phenomenon not explained by the current theory. In addition, because the superconducting state persists up to more manageable temperatures, past the economically-important boiling point of liquid nitrogen (77 kelvins), more commercial applications are feasible, especially if materials with even higher critical temperatures could be discovered. Most of the physical properties of superconductors vary from material to material, such as the heat capacity and the critical temperature, critical field, and critical current density at which superconductivity is destroyed.

On the other hand, there is a class of properties that are independent of the underlying material. For instance, all superconductors have exactly zero resistivity to low applied currents when there is no magnetic field present. The existence of these "universal" properties implies that superconductivity is a thermodynamic phase, and thus possess certain distinguishing properties which are largely independent of microscopic details.

Rainwater harvesting

Rainwater harvesting is a technology used for collecting and storing rainwater from rooftops, the land surface or rock catchments using simple techniques such as jars and pots as well as more complex techniques such as underground check dams. The techniques usually found in Asia and Africa arise from practices employed by ancient civilizations within these regions and still serve as a major source of drinking water supply in rural areas. Commonly used systems are constructed of three principal components; namely, the catchment area, the collection device, and the conveyance system.

Rooftop catchments: In the most basic form of this technology, rainwater is collected in simple vessels at the edge of the roof. Variations on this basic approach include collection of rainwater in gutters which drain to the collection vessel through down-pipes constructed for this purpose, and/or the diversion of rainwater from the gutters to containers for settling particulates before being conveyed to the storage container for the domestic use. As the rooftop is the main catchment area, the amount and quality of rainwater collected depends on the area and type of roofing material. Reasonably pure rainwater can be collected from roofs constructed with galvanized corrugated iron, aluminium or asbestos cement sheets, tiles and slates, although thatched roofs tied with bamboo gutters and laid in proper slopes can produce almost the same amount of runoff less expensively (Gould, 1992).

However, the bamboo roofs are least suitable because of possible health hazards. Similarly, roofs with metallic paint or other coatings are not recommended as they may impart tastes or colour to the collected water. Roof catchments should also be cleaned regularly to remove dust, leaves and bird droppings so as to maintain the quality of the product water (see figure 1). Land surface catchments: Rainwater harvesting using ground or land surface catchment areas is less complex way of collecting rainwater. It involves improving runoff capacity of the land surface through various techniques including collection of runoff with drain pipes and storage of collected water. Compared to rooftop catchment techniques, ground catchment techniques provide more opportunity for collecting water from a larger surface area.

By retaining the flows (including flood flows) of small creeks and streams in small storage reservoirs (on surface or underground) created by low cost (e.g., earthen) dams, this technology can meet water demands during dry periods. There is a possibility of high rates of water loss due to infiltration into the ground, and, because of the often marginal quality of the water collected, this technique is mainly suitable for storing water for agricultural purposes.