1.
Hectare
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The hectare is an SI accepted metric system unit of area equal to 100 ares and primarily used in the measurement of land as a metric replacement for the imperial acre. An acre is about 0.405 hectare and one hectare contains about 2.47 acres, in 1795, when the metric system was introduced, the are was defined as 100 square metres and the hectare was thus 100 ares or 1⁄100 km2. When the metric system was further rationalised in 1960, resulting in the International System of Units, the are was not included as a recognised unit. The hectare, however, remains as a non-SI unit accepted for use with the SI units, the metric system of measurement was first given a legal basis in 1795 by the French Revolutionary government. At the first meeting of the CGPM in 1889 when a new standard metre, manufactured by Johnson Matthey & Co of London was adopted, in 1960, when the metric system was updated as the International System of Units, the are did not receive international recognition. The units that were catalogued replicated the recommendations of the CGPM, many farmers, especially older ones, still use the acre for everyday calculations, and convert to hectares only for official paperwork. Farm fields can have long histories which are resistant to change, with names such as the six acre field stretching back hundreds of years. The names centiare, deciare, decare and hectare are derived by adding the standard metric prefixes to the base unit of area. The centiare is a synonym for one square metre, the deciare is ten square metres. The are is a unit of area, equal to 100 square metres and it was defined by older forms of the metric system, but is now outside of the modern International System of Units. It is commonly used to measure real estate, in particular in Indonesia, India, and in French-, Portuguese-, Slovakian-, Serbian-, Czech-, Polish-, Dutch-, in Russia and other former Soviet Union states, the are is called sotka. It is used to describe the size of suburban dacha or allotment garden plots or small city parks where the hectare would be too large, the decare is derived from deka, the prefix for 10 and are, and is equal to 10 ares or 1000 square metres. It is used in Norway and in the former Ottoman areas of the Middle East, the hectare, although not strictly a unit of SI, is the only named unit of area that is accepted for use within the SI. The United Kingdom, United States, Burma, and to some extent Canada instead use the acre, others, such as South Africa, published conversion factors which were to be used particularly when preparing consolidation diagrams by compilation. In many countries, metrication redefined or clarified existing measures in terms of metric units, non-SI units accepted for use with the International System of Units
2.
Uranium
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Uranium is a chemical element with symbol U and atomic number 92. It is a metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons, Uranium is weakly radioactive because all its isotopes are unstable. The most common isotopes in natural uranium are uranium-238 and uranium-235, Uranium has the highest atomic weight of the primordially occurring elements. Its density is about 70% higher than that of lead, and it occurs naturally in low concentrations of a few parts per million in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite. In nature, uranium is found as uranium-238, uranium-235, Uranium decays slowly by emitting an alpha particle. The half-life of uranium-238 is about 4.47 billion years, many contemporary uses of uranium exploit its unique nuclear properties. Uranium-235 is the naturally occurring fissile isotope, which makes it widely used in nuclear power plants. However, because of the amounts found in nature, uranium needs to undergo enrichment so that enough uranium-235 is present. Uranium-238 is fissionable by fast neutrons, and is fertile, meaning it can be transmuted to fissile plutonium-239 in a nuclear reactor, another fissile isotope, uranium-233, can be produced from natural thorium and is also important in nuclear technology. In sufficient concentration, these maintain a sustained nuclear chain reaction. This generates the heat in nuclear reactors, and produces the fissile material for nuclear weapons. Depleted uranium is used in kinetic energy penetrators and armor plating, Uranium is used as a colorant in uranium glass, producing lemon yellow to green colors. Uranium glass fluoresces green in ultraviolet light and it was also used for tinting and shading in early photography. The 1789 discovery of uranium in the mineral pitchblende is credited to Martin Heinrich Klaproth, eugène-Melchior Péligot was the first person to isolate the metal and its radioactive properties were discovered in 1896 by Henri Becquerel. An ensuing arms race during the Cold War between the United States and the Soviet Union produced tens of thousands of weapons that used uranium metal. The security of those weapons and their fissile material following the breakup of the Soviet Union in 1991 is a concern for public health. When refined, uranium is a white, weakly radioactive metal
3.
Lipid bilayer
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The lipid bilayer is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a barrier around all cells. The cell membranes of almost all living organisms and many viruses are made of a bilayer, as are the membranes surrounding the cell nucleus. The lipid bilayer is the barrier that keeps ions, proteins and other molecules where they are needed, Lipid bilayers are ideally suited to this role because, even though they are only a few nanometers in width, they are impermeable to most water-soluble molecules. Bilayers are particularly impermeable to ions, which allows cells to regulate salt concentrations, biological bilayers are usually composed of amphiphilic phospholipids that have a hydrophilic phosphate head and a hydrophobic tail consisting of two fatty acid chains. Phospholipids with certain groups can alter the surface chemistry of a bilayer and can, for example. Just like the heads, the tails of lipids can also affect membrane properties, the packing of lipids within the bilayer also affects its mechanical properties, including its resistance to stretching and bending. Many of these properties have been studied with the use of model bilayers produced in a lab. Vesicles made by model bilayers have also used clinically to deliver drugs. Biological membranes typically include several types of other than phospholipids. A particularly important example in animal cells is cholesterol, which strengthen the bilayer. Cholesterol also helps regulate the activity of certain integral membrane proteins, integral membrane proteins function when incorporated into a lipid bilayer, and they are held tightly to lipid bilayer with the help of an annular lipid shell. Because bilayers define the boundaries of the cell and its compartments, certain kinds of membrane proteins are involved in the process of fusing two bilayers together. This fusion allows the joining of two structures as in the fertilization of an egg by sperm or the entry of a virus into a cell. Because lipid bilayers are quite fragile and invisible in a traditional microscope, experiments on bilayers often require advanced techniques like electron microscopy and atomic force microscopy. When phospholipids are exposed to water, they self-assemble into a sheet with the hydrophobic tails pointing toward the center of the sheet. This arrangement results in two “leaflets” that are each a single molecular layer, the center of this bilayer contains almost no water and excludes molecules like sugars or salts that dissolve in water. The assembly process is driven by interactions between hydrophobic molecules, an increase in interactions between hydrophobic molecules allows water molecules to bond more freely with each other, increasing the entropy of the system
4.
Red blood cell
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RBCs take up oxygen in the lungs, or gills of fish, and release it into tissues while squeezing through the bodys capillaries. The cytoplasm of erythrocytes is rich in hemoglobin, a biomolecule that can bind oxygen and is responsible for the red color of the cells. In humans, mature red cells are flexible and oval biconcave disks. They lack a nucleus and most organelles, in order to accommodate maximum space for hemoglobin, they can be viewed as sacks of hemoglobin. Approximately 2.4 million new erythrocytes are produced per second in human adults, the cells develop in the bone marrow and circulate for about 100–120 days in the body before their components are recycled by macrophages. Each circulation takes about 60 seconds, approximately a quarter of the cells in the human body are red blood cells. Nearly half of the volume is red blood cells. Red blood cells are known as RBCs, red cells, red blood corpuscles, haematids. Packed red blood cells are red blood cells that have donated, processed. Almost all vertebrates, including all mammals and humans, have red blood cells, red blood cells are cells present in blood in order to transport oxygen. The only known vertebrates without red blood cells are the crocodile icefish, they live in very cold water. While they no longer use hemoglobin, remnants of hemoglobin genes can be found in their genome, oxygen can easily diffuse through the red blood cells cell membrane. Myoglobin, a related to hemoglobin, acts to store oxygen in muscle cells. The color of red cells is due to the heme group of hemoglobin. However, blood can appear bluish when seen through the vessel wall, pulse oximetry takes advantage of the hemoglobin color change to directly measure the arterial blood oxygen saturation using colorimetric techniques. Hemoglobin also has a high affinity for carbon monoxide, forming carboxyhemoglobin which is a very bright red in color. Flushed, confused patients with a reading of 100% on pulse oximetry are sometimes found to be suffering from carbon monoxide poisoning. The red blood cells of mammals are typically shaped as disks, flattened and depressed in the center, with a dumbbell-shaped cross section
5.
Computer monitor
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A computer monitor or a computer display is an electronic visual display for computers. A monitor usually comprises the display device, circuitry, casing, the display device in modern monitors is typically a thin film transistor liquid crystal display or a flat panel LED display, while older monitors used a cathode ray tubes. It can be connected to the computer via VGA, DVI, HDMI, DisplayPort, Thunderbolt, LVDS or other proprietary connectors, originally, computer monitors were used for data processing while television receivers were used for entertainment. From the 1980s onwards, computers have used for both data processing and entertainment, while televisions have implemented some computer functionality. The common aspect ratio of televisions, and computer monitors, has changed from 4,3 to 16,10, to 16,9. Early electronic computers were fitted with a panel of light bulbs where the state of each particular bulb would indicate the state of a particular register bit inside the computer. This allowed the operating the computer to monitor the internal state of the machine. As early monitors were only capable of displaying a limited amount of information. Instead, a printer was the primary output device, while the monitor was limited to keeping track of the programs operation. Multiple technologies have used for computer monitors. Until the 21st century most used cathode ray tubes but they have largely superseded by LCD monitors. The first computer monitors used cathode ray tubes, high-resolution CRT displays were developed for specialized military, industrial and scientific applications but they were far too costly for general use. Either computer could be connected to the terminals of an ordinary color TV set or used with a purpose-made CRT color monitor for optimum resolution. In 1984 IBM introduced the Enhanced Graphics Adapter which was capable of producing 16 colors and had a resolution of 640 x 350, by the end of the 1980s color CRT monitors that could clearly display 1024 x 768 pixels were widely available and increasingly affordable. During the following decade maximum display resolutions gradually increased and prices continued to fall, CRT technology remained dominant in the PC monitor market into the new millennium partly because it was cheaper to produce and offered viewing angles close to 180 degrees. CRTs still offer some image quality advantages over LCDs but improvements to the latter have made much less obvious. There are multiple technologies that have used to implement liquid crystal displays. Commonly, the laptop would be offered with an assortment of display options at increasing price points, monochrome
6.
Mechanical pencil
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A mechanical pencil or a propelling pencil is a pencil with a replaceable and mechanically extendable solid pigment core called a lead /ˈlɛd/. The lead, often made of graphite, is not bonded to the outer casing, other names include automatic pencil, drafting pencil, technical pencil, click pencil, clutch pencil, leadholder, pen pencil, lead pencil, and pacer. Mechanical pencils are used to provide lines of constant width without sharpening in technical drawing and they have also been used for fine-art drawing. Mechanical pencils were first used in the 18th century, with many designs patented in the 19th and 20th centuries, conrad Gesner described a leadholder pencil in 1565, but the lead had to be manually adjusted to sharpen it. The earliest extant example of a pencil was found aboard the wreckage of HMS Pandora. The first patent for a pencil with lead-propelling mechanism was issued to Sampson Mordan. After buying out Hawkins patent rights, Mordan entered into a partnership with Gabriel Riddle from 1823 to 1837. The earliest Mordan pencils are thus hallmarked SMGR, after 1837, Sampson Mordan ended the partnership with Riddle and continued to manufacture pencils as S. MORDAN & CO. His company continued to manufacture pencils and a range of silver objects until World War II. Between 1822 and 1874, more than 160 patents were registered pertaining to a variety of improvements to mechanical pencils, the first spring-loaded mechanical pencil was patented in 1877 and a twist-feed mechanism was developed in 1895. The 0.9 mm lead was introduced in 1938, eventually,1.3 and 1.4 mm mechanisms were available, and 0.4 and 0.2 versions are now produced. The mechanical pencil became successful in Japan with some improvements in 1915 by Tokuji Hayakawa and it was introduced as the Ever-Ready Sharp Pencil. Success was not immediate, since the metal shaft—essential for the pencils long life—was unfamiliar to users, however, the Ever-Ready Sharp began selling in huge numbers after a company from Tokyo and Osaka made large orders. Later, Tokuji Hayakawas company got its name from that pencil, at nearly the same time in the US, Charles R. Keeran was developing a similar pencil that would be the precursor of most of todays pencils. Keerans design was ratchet-based, whereas Hayakawas was screw-based and these two development histories – Hayakawa and Keeran – are often mistakenly combined into one. Keeran patented his lead pencil in 1915 and soon afterwards arranged production, after some improvements, his design was marketed as the Eversharp pencil by the Wahl Adding Machine Company, by the early 1920s, Wahl had sold more than 12,000,000 Eversharps. Mechanical pencils can be divided into two types, those that both hold the lead and can actively propel it forward, and those that only hold the lead in position. Screw-based pencils advance the lead by twisting a screw, which moves a slider down the barrel of the pencil and this was the most common type in the earlier part of the twentieth century
7.
Postage stamp
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Postage stamp may also refer to a formatting artifact in the display of film or video, Windowbox. A postage stamp is a piece of paper that is purchased and displayed on an item of mail as evidence of payment of postage. Typically, stamps are printed on special paper, show a national designation and a denomination on the front. They are sometimes a source of net profit to the issuing agency, stamps are usually rectangular, but triangles or other shapes are occasionally used. The stamp is affixed to an envelope or other postal cover the customer wishes to send, the item is then processed by the postal system, where a postmark, sometimes known as a cancellation mark, is usually applied in overlapping manner to stamp and cover. This procedure marks the stamp as used to prevent its reuse, in modern usage, postmarks generally indicate the date and point of origin of the mailing. The mailed item is delivered to the address the customer has applied to the envelope or parcel. Postage stamps have facilitated the delivery of mail since the 1840s, before then, ink and hand-stamps, usually made from wood or cork, were often used to frank the mail and confirm the payment of postage. The first adhesive postage stamp, commonly referred to as the Penny Black, was issued in the United Kingdom in 1840, there are varying accounts of the inventor or inventors of the stamp. The postage stamp resolved this issue in a simple and elegant manner, concurrently with the first stamps, the UK offered wrappers for mail. S. Postal service for priority or express mailing, the postage stamp afforded convenience for both the mailer and postal officials, more effectively recovered costs for the postal service, and ultimately resulted in a better, faster postal system. With the conveniences stamps offered, their use resulted in greatly increased mailings during the 19th and 20th centuries, as postage stamps with their engraved imagery began to appear on a widespread basis, historians and collectors began to take notice. The study of stamps and their use is referred to as philately. Stamp collecting can be both a hobby and a form of study and reference, as government-issued postage stamps. The postage for the item was prepaid by the use of a hand-stamp to frank the mailed item. Though this stamp was applied to a letter instead of a piece of paper it is considered by many historians as the worlds first postage stamp. Rowland Hill The Englishman Sir Rowland Hill began interest in postal reform in 1835, in 1836, a Member of Parliament, Robert Wallace, provided Hill with numerous books and documents, which Hill described as a half hundred weight of material. Hill commenced a study of these documents, leading him to the 1837 publication of a pamphlet entitled Post Office Reform its Importance
8.
Cigarette
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A cigarette, or cigaret, is a small cylinder of finely cut tobacco leaves rolled in thin paper for smoking. Most modern manufactured cigarettes are filtered, and also include reconstituted tobacco, the term cigarette, as commonly used, refers to a tobacco cigarette, but can apply to similar devices other substances, such as cannabis. A cigarette is distinguished from a cigar by its size, use of processed leaf, and paper wrapping. Cigars are typically composed entirely of whole-leaf tobacco, rates of cigarette smoking vary widely throughout the world and have changed considerably since cigarettes were first widely used in the mid-19th century. While rates of smoking have over time leveled off or declined in the developed world, Cigarettes carry serious health risks, which are more prevalent than with other tobacco products. Nicotine, the psychoactive chemical in tobacco and therefore cigarettes, is very addictive. About half of cigarette smokers die of tobacco-related disease and lose on average 14 years of life, cigarette use by pregnant women has also been shown to cause birth defects, including low birth weight, fetal abnormalities, and premature birth. Second-hand smoke from cigarettes has been shown to be injurious to bystanders, Cigarettes produce an aerosol containing over 4,000 chemical compounds, including nicotine, carbon monoxide, acrolein, and other harmful substances. Over 50 of these are carcinogenic, the earliest forms of cigarettes were similar to their predecessor, the cigar. Cigarettes appear to have had antecedents in Mexico and Central America around the 9th century in the form of reeds, the Maya, and later the Aztecs, smoked tobacco and other psychoactive drugs in religious rituals and frequently depicted priests and deities smoking on pottery and temple engravings. The cigarette and the cigar were the most common methods of smoking in the Caribbean, Mexico, and Central and South America until recent times. The North American, Central American, and South American cigarette used various plant wrappers, when it was back to Spain, maize wrappers were introduced. The resulting product was called papelate and is documented in Goyas paintings La Cometa, La Merienda en el Manzanares, by 1830, the cigarette had crossed into France, where it received the name cigarette, and in 1845, the French state tobacco monopoly began manufacturing them. The first patented cigarette machine was by Juan Nepomuceno Adorno of Mexico in 1847 and this was helped by the development of tobaccos suitable for cigarette use, and by the development of the Egyptian cigarette export industry. Cigarettes may have initially used in a manner similar to pipes, cigars. As cigarette tobacco became milder and more acidic, inhaling may have perceived as more agreeable. However, Moltke noticed in the 1830s that Ottomans inhaled the Turkish tobacco, the widespread smoking of cigarettes in the Western world is largely a 20th-century phenomenon. At the start of the 20th century, the per capita consumption in the USA was 54 cigarettes
9.
Basketball
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Basketball is a non-contact team sport played on a rectangular court by two teams of five players each. The objective is to shoot a ball through a hoop 18 inches in diameter and 10 feet high that is mounted to a backboard at each end of the court. The game was invented in 1891 by Dr. James Naismith, a team can score a field goal by shooting the ball through the basket being defended by the opposition team during regular play. A field goal scores three points for the team if the player shoots from behind the three-point line. A team can also score via free throws, which are worth one point, the team with the most points at the end of the game wins, but additional time is mandated when the score is tied at the end of regulation. The ball can be advanced on the court by passing it to a teammate and it is a violation to lift, or drag, ones pivot foot without dribbling the ball, to carry it, or to hold the ball with both hands then resume dribbling. The game has many techniques for displaying skill—ball-handling, shooting, passing, dribbling, dunking, shot-blocking. The point guard directs the on court action of the team, implementing the coachs game plan, Basketball is one of the worlds most popular and widely viewed sports. Outside North America, the top clubs from national leagues qualify to continental championships such as the Euroleague, the FIBA Basketball World Cup attracts the top national teams from around the world. Each continent hosts regional competitions for teams, like EuroBasket. The FIBA Womens Basketball World Cup features the top womens basketball teams from continental championships. The main North American league is the WNBA, whereas the EuroLeague Women has been dominated by teams from the Russian Womens Basketball Premier League, in early December 1891, Canadian Dr. He sought a vigorous indoor game to keep his students occupied, 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 elevated track. Basketball was originally played with a soccer ball and these laces could cause bounce passes and dribbling to be unpredictable. Eventually a lace-free ball construction method was invented, and this change to the game was endorsed by Naismith, dribbling was not part of the original game except for the bounce pass to teammates. Passing the ball was the means of ball movement. Dribbling was eventually introduced but limited by the shape of early balls. Dribbling only became a part of the game around the 1950s
10.
Volleyball
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Volleyball is a team sport in which two teams of six players are separated by a net. Each team tries to points by grounding a ball on the other teams court under organized rules. It has been a part of the program of the Summer Olympic Games since 1964. The receiving team must not let the ball be grounded within their court, the team may touch the ball up to 3 times but individual players may not touch the ball twice consecutively. The team that wins the rally is awarded a point, the ball is usually played with the hands or arms, but players can legally strike or push the ball with any part of the body. A number of consistent techniques have evolved in volleyball, including spiking and blocking as well as passing, setting, the game took some of its characteristics from tennis and handball. Another indoor sport, basketball, was catching on in the area, having been invented just ten miles away in the city of Springfield, Massachusetts, only four years before. Mintonette was designed to be a sport, less rough than basketball, for older members of the YMCA. The first rules, written down by William G Morgan, called for a net 6 ft 6 in high, a 25 ft ×50 ft court, and any number of players. A match was composed of nine innings with three serves for each team in each inning, and no limit to the number of contacts for each team before sending the ball to the opponents court. In case of an error, a second try was allowed. Hitting the ball into the net was considered a foul —except in the case of the first-try serve, Volleyball rules were slightly modified by the International YMCA Training School and the game spread around the country to various YMCAs. The first official ball used in volleyball is disputed, some say that Spalding created the first official ball in 1896. In 1917, the game was changed from 21 to 15 points, in 1919, about 16,000 volleyballs were distributed by the American Expeditionary Forces to their troops and allies, which sparked the growth of volleyball in new countries. The first country outside the United States to adopt volleyball was Canada in 1900, an international federation, the Fédération Internationale de Volleyball, was founded in 1947, and the first World Championships were held in 1949 for men and 1952 for women. The sport is now popular in Brazil, in Europe, in Russia, and in countries including China. Beach volleyball, a variation of the played on sand. Volleyball is also a sport at the Paralympics managed by the World Organization Volleyball for Disabled, nudists were early adopters of the game with regular organized play in clubs as early as the late 1920s
11.
Suburb
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A suburb is a residential area or a mixed use area, either existing as part of a city or urban area or as a separate residential community within commuting distance of a city. In some areas, such as Australia, China, New Zealand, the United Kingdom, and a few U. S. states, new suburbs are routinely annexed by adjacent cities. In others, such as Arabia, Canada, France, and much of the United States, Suburbs first emerged on a large scale in the 19th and 20th centuries as a result of improved rail and road transport, which led to an increase in commuting. Suburbs tend to proliferate around cities that have an abundance of adjacent flat land, the English word is derived from the Old French subburbe, which is in turn derived from the Latin suburbium, formed from sub and urbs. The first recorded usage of the term in English, was made by John Wycliffe in 1380, in Australia and New Zealand, suburbs have become formalised as geographic subdivisions of a city and are used by postal services in addressing. In rural areas in both countries, their equivalents are called localities, the terms inner suburb and outer suburb are used to differentiate between the higher-density suburbs in proximity to the city center, and the lower-density suburbs on the outskirts of the urban area. The term middle suburbs is also used, Suburbs, in this sense, can range from areas that seem more like residential areas of a city proper to areas separated by open countryside from the city centre. In large cities such as London, suburbs include formerly separate towns and villages that have been gradually absorbed during a growth and expansion. In the United States and Canada, suburb can refer either to an residential area of a city or town or to a separate municipality or unincorporated area outside a town or city. The earliest appearance of suburbs coincided with the spread of the first urban settlements, large walled towns tended to be the focus around which smaller villages grew up in a symbiotic relationship with the market town. The word suburbani was first used by the Roman statesman Cicero in reference to the large villas, as populations grew during the Early Modern Period in Europe, urban towns swelled with a steady influx of people from the countryside. In some places, nearby settlements were swallowed up as the city expanded. The peripheral areas on the outskirts of the city were generally inhabited by the very poorest, by the mid-19th century, the first major suburban areas were springing up around London as the city became more overcrowded and unsanitary. A major catalyst in suburban growth came from the opening of the Metropolitan Railway in the 1860s, the line joined the capitals financial heart in the City to what were to become the suburbs of Middlesex. Harrow was reached in 1880, and the line extended as far as Verney Junction in Buckinghamshire, more than 50 miles from Baker Street. Unlike other railway companies, which were required to dispose of surplus land, in 1912, it was suggested that a specially formed company should take over from the Surplus Lands Committee and develop suburban estates near the railway. However, World War I delayed these plans and it was only in 1919, with expectation of a housing boom. The term Metro-land was coined by the Mets marketing department in 1915 when the Guide to the Extension Line became the Metro-land guide and this promoted the land served by the Met for the walker, visitor and later the house-hunter
12.
Tennis court
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A tennis court is the venue where the sport of tennis is played. It is a rectangular surface with a low net stretched across the center. The same surface can be used to play doubles and singles matches. A variety of surfaces can be used to create a tennis court, Tennis is played on a rectangular flat surface, usually of grass, clay or hard material. The dimensions of a court are defined and regulated by the International Tennis Federation governing body and are written down in the annual Rules of Tennis document. The court is 78 feet long and its width is 27 feet for singles matches and 36 feet for doubles matches. The service line is 21 feet from the net, additional clear space around the court is needed in order for players to reach overrun balls for a total of 60 feet wide and 120 feet long. A net is stretched across the width of the court, parallel with the baselines. The net is 3 feet 6 inches high at the posts, the net posts are 3 feet outside the doubles court on each side or, for a singles net,3 feet outside the singles court on each side. Tennis is played on a variety of surfaces and each surface has its own characteristics which affect the style of the game. There are four types of courts depending on the materials used for the court surface, clay courts, hard courts, grass courts. The Australian Open switched to hard courts in 1988 and in its years the French championship alternated between clay and sand/rubble courts. ITF uses the classification for tennis court surface types, Clay courts are made of crushed shale, stone. The French Open is the only Grand Slam tournament to use clay courts, Clay courts slow down the ball and produce a high bounce in comparison to grass courts or hard courts. For this reason, the court takes away many of the advantages of big serves. Clay courts are cheaper to construct than other types of tennis courts, Clay courts need to be rolled to preserve flatness. The clays water content must be balanced, green courts generally require the courts to be sloped to allow water run-off, Clay courts are more common in Europe and Latin America than in North America and tend to heavily favour baseline players. Grass courts are the fastest type of courts in common use and they consist of grass grown on very hard-packed soil, which adds additional variables, bounces depend on how healthy the grass is, how recently it has been mown, and the wear and tear of recent play
. PMID 16055528. Retrieved 2011-09-27.
