title: Vehicle content: is very important in many vehicles. The main sources of friction are rolling friction and fluid drag (air drag or water drag). Wheels have low bearing friction and pneumatic tyres give low rolling friction. Steel wheels on steel tracks are lower still. Aerodynamic drag can be reduced by streamlined design features. Friction is desirable and important in supplying traction to facilitate motion on land. Most land vehicles rely on friction for accelerating, decelerating and changing direction. Sudden reductions in traction can cause loss of control and accidents. Most vehicles, with the notable exception of railed vehicles, have at least one


title: Vehicle content: steering mechanism. Wheeled vehicles steer by angling their front or rear wheels. The B-52 Stratofortress has a special arrangement in which all four main wheels can be angled. Skids can also be used to steer by angling them, as in the case of a snowmobile. Ships, boats, submarines, dirigibles and aeroplanes usually have a rudder for steering. On an airplane, ailerons are used to bank the airplane for directional control, sometimes assisted by the rudder. With no power applied, most vehicles come to a stop due to friction. But it is often required to stop a vehicle faster than by


title: Vehicle content: friction alone: so almost all vehicles are equipped with a braking system. Wheeled vehicles are typically equipped with friction brakes, which use the friction between brake pads (stators) and brake rotors to slow the vehicle. Many airplanes have high performance versions of the same system in their landing gear for use on the ground. A Boeing 757 brake, for example, has 3 stators and 4 rotors. The Space Shuttle also uses frictional brakes on its wheels. As well as frictional brakes, hybrid/electric cars, trolleybuses and electric bicycles can also use regenerative brakes to recycle some of the vehicle's potential energy.


title: Vehicle content: High-speed trains sometimes use frictionless Eddy-current brakes; however widespread application of the technology has been limited by overheating and interference issues. Aside from landing gear brakes, most large aircraft have other ways of decelerating. In aircraft, air brakes are aerodynamic surfaces that create friction, with the air flow causing the vehicle to slow. These are usually implemented as flaps that oppose air flow when extended and are flush with aircraft when retracted. Reverse thrust is also used in many aeroplane engines. Propeller aircraft achieve reverse thrust by reversing the pitch of the propellers, while jet aircraft do so by redirecting


title: Vehicle content: their engine exhaust forwards. On aircraft carriers, arresting gears are used to stop an aircraft. Pilots may even apply full forward throttle on touchdown, in case the arresting gear does not catch and a go around is needed. Parachutes are used to slow down vehicles travelling very fast. Parachutes have been used in land, air and space vehicles such as the ThrustSSC, Eurofighter Typhoon and Apollo Command Module. Some older Soviet passenger jets had braking parachutes for emergency landings. Boats use similar devices called sea anchors to maintain stability in rough seas. To further increase the rate of deceleration or


title: Vehicle content: where the brakes have failed, several mechanisms can be used to stop a vehicle. Cars and rolling stock usually have hand brakes that, while designed to secure an already parked vehicle, can provide limited braking should the primary brakes fail. A secondary procedure called forward-slip is sometimes used to slow airplanes by flying at an angle, causing more drag. Motor vehicle and trailer categories are defined according to the following international classification: In the European Union the classifications for vehicle types are defined by: European Community, is based on the Community's WVTA (whole vehicle type-approval) system. Under this system, manufacturers


title: Vehicle content: can obtain certification for a vehicle type in one Member State if it meets the EC technical requirements and then market it EU-wide with no need for further tests. Total technical harmonization already has been achieved in three vehicle categories (passenger cars, motorcycles, and tractors) and soon will extend to other vehicle categories (coaches and utility vehicles). It is essential that European car manufacturers be ensured access to as large a market as possible. While the Community type-approval system allows manufacturers to benefit fully from internal market opportunities, worldwide technical harmonization in the context of the United Nations Economic Commission


title: Vehicle content: for Europe (UNECE) offers a market beyond European borders. In many cases, it is unlawful to operate a vehicle without a license or certification. The least strict form of regulation usually limits what passengers the driver may carry or prohibits them completely (e.g., a Canadian ultra-light license without endorsements). The next level of licensing may allow passengers, but without any form of compensation or payment. A private driver's license usually has these conditions. Commercial licenses that allow the transport of passengers and cargo are more tightly regulated. The most strict form of licensing is generally reserved for school buses, hazardous


title: Vehicle content: materials transports and emergency vehicles. The driver of a motor vehicle is typically required to hold a valid driver's license while driving on public lands, whereas the pilot of an aircraft must have a license at all times, regardless of where in the jurisdiction the aircraft is flying. Vehicles are often required to be registered. Registration may be for purely legal reasons, for insurance reasons or to help law enforcement recover stolen vehicles. Toronto Police Service, for example, offers free and optional bicycle registration online. On motor vehicles, registration often takes the form of a vehicle registration plate, which makes


title: Vehicle content: it easy to identify a vehicle. In Russia, trucks and buses have their licence plate numbers repeated in large black letters on the back. On aircraft, a similar system is used where a tail number is painted on various surfaces. Like motor vehicles and aircraft, watercraft also have registration numbers in most jurisdictions, however the vessel name is still the primary means of identification as has been the case since ancient times. For this reason, duplicate registration names are generally rejected. In Canada, boats with an engine power of or greater require registration, leading to the ubiquitous "" engine. Registration


title: Vehicle content: may be conditional on the vehicle being approved for use on public highways, as in the case of the UK and Ontario. Many US states also have requirements for vehicles operating on public highways. Aircraft have more stringent requirements, as they pose a high risk of damage to people and property in event of an accident. In the US, the FAA requires aircraft to have an airworthiness certificate. Because US aircraft must be flown for some time before they are certified, there is a provision for an experimental airworthiness certificate. FAA experimental aircraft are restricted in operation, including no overflights


title: Vehicle content: of populated areas, in busy airspace or with unessential passengers. Materials and parts used in FAA certified aircraft must meet the criteria set forth by the "technical standard orders". In many jurisdictions, the operator of a vehicle is legally obligated to carry safety equipment with or on them. Common examples include seat belts in cars, helmets on motorcycles and bicycles, fire extinguishers on boats, buses and airplanes and life jackets on boats and commercial aircraft. Passenger aircraft carry a great deal of safety equipment including inflatable slides are rafts, oxygen masks, oxygen tanks, life jackets, satellite beacons and first aid


title: Vehicle content: kits. Some equipment such as life jackets has led to debate regarding their usefulness. In the case of Ethiopian Airlines Flight 961, the life jackets saved many people but also led to many deaths when passengers inflated their vests prematurely. There are specific real-estate arrangements made to allow vehicles to travel from one place to another. The most common such arrangements are public highways, where appropriately licensed vehicles can navigate without hindrance. These highways are on public land and are maintained by the government. Similarly, toll routes are open to the public after paying a toll. These routes and the


title: Vehicle content: land they rest on may be government or privately owned or a combination of both. Some routes are privately owned but grant access to the public. These routes often have a warning sign stating that the government does not maintain the way. An example of this are byways in England and Wales. In Scotland, land is open to un-motorised vehicles if the land meets certain criteria. Public land is sometimes open to use by off-road vehicles. On US public land, the Bureau of Land Management (BLM) decides where vehicles may be used. Railways often pass over land not owned by


title: Vehicle content: the railway company. The right to this land is granted to the railway company through mechanisms such as easement. Watercraft are generally allowed to navigate public waters without restriction as long as they do not cause a disturbance. Passing through a lock, however, may require paying a toll. Despite the common law tradition "Cuius est solum, eius est usque ad coelum et ad inferos" of owning all the air above one's property, the US Supreme Court ruled that aircraft in the US have the right to use air above someone else's property without their consent. While the same rule generally


title: Vehicle content: applies in all jurisdictions, some countries such as Cuba and Russia have taken advantage of air rights on a national level to earn money. There are some areas that aircraft are barred from overflying. This is called prohibited airspace. Prohibited airspace is usually strictly enforced due to potential damage from espionage or attack. In the case of Korean Air Lines Flight 007, the airliner entered prohibited airspace over Soviet territory and was shot down as it was leaving. For a comparison of transportation fatality rates, see: Air safety statistics. Several different metrics used to compare and evaluate the safety of


title: Vehicle content: different vehicles. The main three are "deaths per billion passenger-journeys", "deaths per billion passenger-hours" and "deaths per billion passenger-kilometers". Vehicle A vehicle (from ) is a machine that transports people or cargo. Vehicles include wagons, bicycles, motor vehicles (motorcycles, cars, trucks, buses), railed vehicles (trains, trams), watercraft (ships, boats), amphibious vehicles (screw-propelled vehicle, hovercraft), aircraft (airplanes, helicopters) and spacecraft. Land vehicles are classified broadly by what is used to apply steering and drive forces against the ground: wheeled, tracked, railed or skied. ISO 3833-1977 is the standard, also internationally used in legislation, for road vehicles types, terms and definitions. There


title: Violin content: Violin The violin, also known informally as a fiddle, is a wooden string instrument in the violin family. Most violins have a hollow wooden body. It is the smallest and highest-pitched instrument in the family in regular use. Smaller violin-type instruments are known, including the violino piccolo and the kit violin, but these are virtually unused. The violin typically has four strings tuned in perfect fifths, and is most commonly played by drawing a bow across its strings, though it can also be played by plucking the strings with the fingers (pizzicato) and by striking the strings with the wooden


title: Violin content: side of the bow (col legno). Violins are important instruments in a wide variety of musical genres. They are most prominent in the Western classical tradition, both in ensembles (from chamber music to orchestras) and as solo instruments and in many varieties of folk music, including country music, bluegrass music and in jazz. Electric violins with solid bodies and piezoelectric pickups are used in some forms of rock music and jazz fusion, with the pickups plugged into instrument amplifiers and speakers to produce sound. Further, the violin has come to be played in many non-Western music cultures, including Indian music


title: Violin content: and Iranian music. The name "fiddle" is often used regardless of the type of music played on it. The violin was first known in 16th-century Italy, with some further modifications occurring in the 18th and 19th centuries to give the instrument a more powerful sound and projection. In Europe, it served as the basis for the development of other stringed instruments used in Western classical music, such as the viola. Violinists and collectors particularly prize the fine historical instruments made by the Stradivari, Guarneri and Amati families from the 16th to the 18th century in Brescia and Cremona (Italy) and


title: Violin content: by Jacob Stainer in Austria. According to their reputation, the quality of their sound has defied attempts to explain or equal it, though this belief is disputed. Great numbers of instruments have come from the hands of less famous makers, as well as still greater numbers of mass-produced commercial "trade violins" coming from cottage industries in places such as Saxony, Bohemia, and Mirecourt. Many of these trade instruments were formerly sold by Sears, Roebuck and Co. and other mass merchandisers. The parts of a violin are usually made from different types of wood (although electric violins may not be made


title: Violin content: of wood at all, since their sound may not be dependent on specific acoustic characteristics of the instrument's construction, but rather an electronic pickup, amplifier and speaker). Violins can be strung with gut, Perlon or other synthetic, or steel strings. A person who makes or repairs violins is called a luthier or violinmaker. One who makes or repairs bows is called an "archetier" or bowmaker. The word "violin" was first used in English in the 1570s. The word "violin" comes from "Italian "violino", [a] diminutive of viola". The term "viola" comes from the expression for "tenor violin" in 1797, from


title: Violin content: Italian "viola", from Old Provençal "viola", [which came from] Medieval Latin "vitula"" as a term which means "stringed instrument," perhaps [coming] from Vitula, Roman goddess of joy..., or from related Latin verb "vitulari", "to exult, be joyful." The related term ""Viola da gamba"" means "bass viol" (1724) is from Italian, literally "a viola for the leg" (i.e. to hold between the legs)." A violin is the "modern form of the smaller, medieval viola da braccio." The violin is often called a fiddle, either when used in a folk music context, or even in Classical music scenes, as an informal nickname


title: Violin content: for the instrument. The word "fiddle" was first used in English in the late 14th century. The word "fiddle" comes from "fedele, fydyll, fidel, earlier fithele, from Old English "fiðele" "fiddle," which is related to Old Norse "fiðla", Middle Dutch "vedele", Dutch "vedel", Old High German "fidula", German "Fiedel", "a fiddle;" all of uncertain origin." As to the origin of the word "fiddle", the "...usual suggestion, based on resemblance in sound and sense, is that it is from Medieval Latin "vitula"." The "Online Etymology Dictionary" states that the term "fiddle" has "...been relegated to colloquial usage by its more proper


title: Violin content: cousin, violin, a process encouraged by phraseology such as 'fiddlesticks' (1620s), [the] contemptuous nonsense word 'fiddle-de-dee' (1784), and [expressions like] 'fiddle-faddle'." The earliest stringed instruments were mostly plucked (for example, the Greek lyre). Two-stringed, bowed instruments, played upright and strung and bowed with horsehair, may have originated in the nomadic equestrian cultures of Central Asia, in forms closely resembling the modern-day Mongolian Morin huur and the Kazakh Kobyz. Similar and variant types were probably disseminated along East-West trading routes from Asia into the Middle East, and the Byzantine Empire. The first makers of violins probably borrowed from various developments of


title: Violin content: the Byzantine lyra. These included the rebec, the Arabic "rebab" (ربابة), the vielle (also known as the "fidel" or "viuola") and the "lira da braccio". The violin in its present form emerged in early 16th-century northern Italy. The earliest pictures of violins, albeit with three strings, are seen in northern Italy around 1530, at around the same time as the words "violino" and "vyollon" are seen in Italian and French documents. One of the earliest explicit descriptions of the instrument, including its tuning, is from the "Epitome musical" by Jambe de Fer, published in Lyon in 1556. By this time,


title: Violin content: the violin had already begun to spread throughout Europe. The violin proved very popular, both among street musicians and the nobility; the French king Charles IX ordered Andrea Amati to construct 24 violins for him in 1560. One of these "noble" instruments, the "Charles IX", is the oldest surviving violin. The finest Renaissance carved and decorated violin in the world is the Gasparo da Salò (1574) owned by Ferdinand II, Archduke of Austria and later, from 1841, by the Norwegian virtuoso Ole Bull, who used it for forty years and thousands of concerts, for its very powerful and beautiful tone,


title: Violin content: similar to that of a Guarneri. "The Messiah" or ""Le Messie"" (also known as the "Salabue") made by Antonio Stradivari in 1716 remains pristine. It is now located in the Ashmolean Museum of Oxford. The most famous (luthiers) between the 16th century and the 18th century include: Significant changes occurred in the construction of the violin in the 18th century, particularly in the length and angle of the neck, as well as a heavier bass bar. The majority of old instruments have undergone these modifications, and hence are in a significantly different state than when they left the hands of


title: Violin content: their makers, doubtless with differences in sound and response. But these instruments in their present condition set the standard for perfection in violin craftsmanship and sound, and violin makers all over the world try to come as close to this ideal as possible. To this day, instruments from the so-called Golden Age of violin making, especially those made by Stradivari, Guarneri del Gesù and Montagnana are the most sought-after instruments by both collectors and performers. The current record amount paid for a Stradivari violin is £9.8 million (US$15.9 million), when the instrument known as the Lady Blunt was sold by


title: Violin content: Tarisio Auctions in an online auction on June 20, 2011. A violin generally consists of a spruce top (the soundboard, also known as the "top plate", "table", or "belly"), maple ribs and back, two endblocks, a neck, a bridge, a soundpost, four strings, and various fittings, optionally including a chinrest, which may attach directly over, or to the left of, the tailpiece. A distinctive feature of a violin body is its hourglass-like shape and the arching of its top and back. The hourglass shape comprises two upper bouts, two lower bouts, and two concave C-bouts at the "waist", providing clearance


title: Violin content: for the bow. The "voice" or sound of a violin depends on its shape, the wood it is made from, the graduation (the thickness profile) of both the top and back, the varnish that coats its outside surface and the skill of the luthier in doing all of these steps. The varnish and especially the wood continue to improve with age, making the fixed supply of old well-made violins built by famous luthiers much sought-after. The majority of glued joints in the instrument use animal hide glue rather than common white glue for a number of reasons. Hide glue is


title: Violin content: capable of making a thinner joint than most other glues, it is reversible (brittle enough to crack with carefully applied force, and removable with very warm water) when disassembly is needed, and since fresh hide glue sticks to old hide glue, more original wood can be preserved when repairing a joint. (More modern glues must be cleaned off entirely for the new joint to be sound, which generally involves scraping off some wood along with the old glue.) Weaker, diluted glue is usually used to fasten the top to the ribs, and the nut to the fingerboard, since common repairs


title: Violin content: involve removing these parts. The purfling running around the edge of the spruce top provides some protection against cracks originating at the edge. It also allows the top to flex more independently of the rib structure. Painted-on faux purfling on the top is usually a sign of an inferior instrument. The back and ribs are typically made of maple, most often with a matching striped figure, referred to as "flame", "fiddleback", or "tiger stripe". The neck is usually maple with a flamed figure compatible with that of the ribs and back. It carries the fingerboard, typically made of ebony, but


title: Violin content: often some other wood stained or painted black on cheaper instruments. Ebony is the preferred material because of its hardness, beauty, and superior resistance to wear. Fingerboards are dressed to a particular transverse curve, and have a small lengthwise "scoop," or concavity, slightly more pronounced on the lower strings, especially when meant for gut or synthetic strings. Some old violins (and some made to appear old) have a grafted scroll, evidenced by a glue joint between the pegbox and neck. Many authentic old instruments have had their necks reset to a slightly increased angle, and lengthened by about a centimeter.


title: Violin content: The neck graft allows the original scroll to be kept with a Baroque violin when bringing its neck into conformance with modern standards. The bridge is a precisely cut piece of maple that forms the lower anchor point of the vibrating length of the strings and transmits the vibration of the strings to the body of the instrument. Its top curve holds the strings at the proper height from the fingerboard in an arc, allowing each to be sounded separately by the bow. The sound post, or "soul post", fits precisely inside the instrument between the back and top, below


title: Violin content: the treble foot of the bridge, which it helps support. It also transmits vibrations between the top and the back of the instrument. The tailpiece anchors the strings to the lower bout of the violin by means of the tailgut, which loops around an ebony button called the tailpin (sometimes confusingly called the "endpin", like the cello's spike), which fits into a tapered hole in the bottom block. Very often the E string will have a fine tuning lever worked by a small screw turned by the fingers. Fine tuners may also be applied to the other strings, especially on


title: Violin content: a student instrument, and are sometimes built into the tailpiece. The fine tuners enable the performer to make small changes in the pitch of a string. At the scroll end, the strings wind around the wooden tuning pegs in the pegbox. The tuning pegs are tapered and fit into holes in the peg box. The tuning pegs are held in place by the friction of wood on wood. Strings may be made of metal or less commonly gut or gut wrapped in metal. Strings usually have a colored silk wrapping at both ends, for identification of the string (e.g., G


title: Violin content: string, D string, A string or E string) and to provide friction against the pegs. The tapered pegs allow friction to be increased or decreased by the player applying appropriate pressure along the axis of the peg while turning it. Strings were first made of sheep gut (commonly known as catgut, which despite the name, did not come from cats), or simply gut, which was stretched, dried, and twisted. In the early years of the 20th century, strings were made of either gut or steel. Modern strings may be gut, solid steel, stranded steel, or various synthetic materials such as


title: Violin content: perlon, wound with various metals, and sometimes plated with silver. Most E strings are unwound, either plain or plated steel. Gut strings are not as common as they once were, but many performers use them to achieve a specific sound especially in historically informed performance of Baroque music. Strings have a limited lifetime. Eventually, when oil, dirt, corrosion, and rosin accumulate, the mass of the string can become uneven along its length. Apart from obvious things, such as the winding of a string coming undone from wear, players generally change a string when it no longer plays "true" (with good


title: Violin content: intonation on the harmonics), losing the desired tone, brilliance and intonation. String longevity depends on string quality and playing intensity. A violin is tuned in fifths, in the notes G, D, A, E. The lowest note of a violin, tuned normally, is G, or G below middle C. (On rare occasions, the lowest string may be tuned down by as much as a fourth, to D.) The highest note is less well defined: E, the E two octaves above the open string (which is tuned to E) may be considered a practical limit for orchestral violin parts, but it is


title: Violin content: often possible to play higher, depending on the length of the fingerboard and the skill of the violinist. Yet higher notes (up to C) can be sounded by stopping the string, reaching the limit of the fingerboard, or by using artificial harmonics. The arched shape, the thickness of the wood, and its physical qualities govern the sound of a violin. Patterns of the node made by sand or glitter sprinkled on the plates with the plate vibrated at certain frequencies, called "Chladni patterns", are occasionally used by luthiers to verify their work before assembling the instrument. Apart from the standard,


title: Violin content: "full" () size, violins are also made in so-called "fractional" sizes of , , , , , , , and even . These smaller instruments are commonly used by young players, whose fingers are not long enough to reach the correct positions on full-sized instruments. While related in some sense to the dimensions of the instruments, the fractional sizes are not intended to be literal descriptions of relative proportions. For example, a -sized instrument is not three-quarters the length of a full size instrument. The body length (not including the neck) of a full-size, or , violin is , smaller


title: Violin content: in some 17th-century models. A violin's body length is , and a size is . With the violin's closest family member, the viola, size is specified as body length in inches or centimeters rather than fractional sizes. A full-size viola averages . However, each individual adult will determine which size of viola to use. Occasionally, an adult with a small frame may use a so-called size violin instead of a full-size instrument. Sometimes called a "lady's violin", these instruments are slightly shorter than a full size violin, but tend to be high-quality instruments capable of producing a sound that is


title: Violin content: comparable to that of fine full size violins. 5 String violin sizes may differ from the normal 4 string. The instrument which corresponds to the violin in the violin octet is the mezzo violin, tuned the same as a violin but with a slightly longer body. The strings of the mezzo violin are the same length as those of the standard violin. Violins are tuned by turning the pegs in the pegbox under the scroll, or by adjusting the "fine tuner" screws at the tailpiece. All violins have pegs; fine tuners (also called "fine adjusters") are optional. Most fine tuners


title: Violin content: consist of a metal screw that moves a lever attached to the string end. They permit very small pitch adjustments much more easily than the pegs. By turning one clockwise, the pitch becomes sharper (as the string is under more tension) and turning one counterclockwise, the pitch becomes flatter (as the string is under less tension). Fine tuners on all four of the strings are very helpful when using those that have a steel core, and some players use them with synthetic strings as well. Since modern E strings are steel, a fine tuner is nearly always fitted for that


title: Violin content: string. Fine tuners are not used with gut strings, which are more elastic than steel or synthetic-core strings and do not respond adequately to the very small movements of fine tuners. To tune a violin, the A string is first tuned to a standard pitch (usually 440 Hz). (When accompanying or playing with a fixed-pitch instrument such as a piano or accordion, the violin tunes to it.) The other strings are then tuned against each other in intervals of perfect fifths by bowing them in pairs. A minutely higher tuning is sometimes employed for solo playing to give the instrument


title: Violin content: a brighter sound; conversely, Baroque music is sometimes played using lower tunings to make the violin's sound more gentle. After tuning, the instrument's bridge may be examined to ensure that it is standing straight and centered between the inner nicks of the f-holes; a crooked bridge may significantly affect the sound of an otherwise well-made violin. After extensive playing, the holes into which the tuning pegs are inserted can become worn, which can lead the peg to slip under tension. This can lead to the pitch of the string dropping, or if the peg becomes completely loose, to the string


title: Violin content: completely losing tension. A violin in which the tuning pegs are slipping needs to be repaired by a luthier or violin repairperson. Peg dope or peg compound, used regularly, can delay the onset of such wear, while allowing the pegs to turn smoothly. The tuning G–D–A–E is used for most violin music, both in Classical music, jazz and folk music. Other tunings are occasionally employed; the G string, for example, can be tuned up to A. The use of nonstandard tunings in classical music is known as "scordatura"; in some folk styles, it is called "cross tuning". One famous example


title: Violin content: of scordatura in classical music is Camille Saint-Saëns' "Danse Macabre", where the solo violin's E string is tuned down to E to impart an eerie dissonance to the composition. Other examples are the third movement of "Contrasts", by Béla Bartók, where the E string is tuned down to E and the G tuned to a G, and the Mystery Sonatas by Biber, in which each movement has different scordatura tuning. In Indian classical music and Indian light music, the violin is likely to be tuned to D–A–D–A in the South Indian style. As there is no concept of absolute pitch


title: Violin content: in Indian classical music, any convenient tuning maintaining these relative pitch intervals between the strings can be used. Another prevalent tuning with these intervals is B–F–B–F, which corresponds to Sa–Pa–Sa–Pa in the Indian carnatic classical music style. In the North Indian Hindustani style, the tuning is usually Pa-Sa-Pa-Sa instead of Sa–Pa–Sa–Pa. This could correspond to F–B–F–B, for instance. In Iranian classical music and Iranian light music, the violin ls different tunings in any Dastgah, the violin is likely to be tuned (E–A–E–A) in Dastgah-h Esfahan or in Dastgāh-e Šur is (E–A–D–E) and (E–A–E–E), in Dastgāh-e Māhur is (E–A–D–A). In Arabic


title: Violin content: classical music, the A and E strings are lowered by a whole step i.e. G–D–G–D. This is to ease playing Arabic maqams, especially those containing quarter tones. While most violins have four strings, there are violins with additional strings. Some have as many as seven strings. Seven strings is generally thought to be the maximum number of strings that can be put on a bowed string instrument, because with more than seven strings, it would be impossible to play a particular inner string individually with the bow. Instruments with seven strings are very rare. The extra strings on such violins


title: Violin content: typically are lower in pitch than the G-string; these strings are usually tuned to C, F, and B. If the instrument's playing length, or string length from nut to bridge, is equal to that of an ordinary full-scale violin; i.e., a bit less than , then it may be properly termed a violin. Some such instruments are somewhat longer and should be regarded as violas. Violins with five strings or more are typically used in jazz or folk music. Some custom-made instruments have extra strings which are not bowed, but which sound sympathetically, due to the vibrations of the bowed


title: Violin content: strings. A violin is usually played using a bow consisting of a stick with a ribbon of horsehair strung between the tip and frog (or nut, or heel) at opposite ends. A typical violin bow may be overall, and weigh about . Viola bows may be about shorter and heavier. At the frog end, a screw adjuster tightens or loosens the hair. Just forward of the frog, a leather thumb cushion, called the grip, and winding protect the stick and provide a strong grip for the player's hand. Traditional windings are of wire (often silver or plated silver), silk, or


title: Violin content: baleen ("whalebone", now substituted by alternating strips of tan and black plastic.) Some fiberglass student bows employ a plastic sleeve as grip and winding. Bow hair traditionally comes from the tail of a grey male horse (which has predominantly white hair). Some cheaper bows use synthetic fiber. Solid rosin is rubbed onto the hair, to render it slightly sticky; when the bow is drawn across a string, the friction between them makes the string vibrate. Traditional materials for the more costly bow sticks include snakewood, and brazilwood (which is also known as Pernambuco wood). Some recent bow design innovations use


title: Violin content: carbon fiber (CodaBows) for the stick, at all levels of craftsmanship. Inexpensive bows for students are made of less costly timbers, or from fiberglass (Glasser). The violin is played either seated or standing up. Solo players (whether playing alone, with a piano or with an orchestra) play mostly standing up (unless prevented by a physical disability such as in the case of Itzhak Perlman), while in the orchestra and in chamber music it is usually played seated. In the 2000s and 2010s, some orchestras performing Baroque music (such as the Freiburg Baroque Orchestra) have had all of their violins and


title: Violin content: violas, solo and ensemble, perform standing up. The standard way of holding the violin is with the left side of the jaw resting on the chinrest of the violin, and supported by the left shoulder, often assisted by a shoulder rest (or a sponge and an elastic band for younger players who struggle with shoulder rests). The jaw and the shoulder must hold the violin firmly enough to allow it to remain stable when the left hand goes from a high position (a high pitched note far up on the fingerboard) to a low one (nearer to the pegbox). In


title: Violin content: the Indian posture, the stability of the violin is guaranteed by its scroll resting on the side of the foot. While teachers point out the vital importance of good posture both for the sake of the quality of the playing and to reduce the chance of repetitive strain injury, advice as to what good posture is and how to achieve it differs in details. However all insist on the importance of a natural relaxed position without tension or rigidity. Things which are almost universally recommended is keeping the left wrist straight (or very nearly so) to allow the fingers of


title: Violin content: the left hand to move freely and to reduce the chance of injury and keeping either shoulder in a natural relaxed position and avoiding raising either of them in an exaggerated manner. This, like any other unwarranted tension, would limit freedom of motion, and increase the risk of injury. Hunching can hamper good playing, because it throws the body off balance and makes the shoulders rise. Another sign that comes from unhealthy tension is pain in the left hand, which indicates too much pressure when holding the violin. The left hand determines the sounding length of the string, and thus


title: Violin content: the pitch of the string, by "stopping" it (pressing it) against the fingerboard with the fingertips, producing different pitches. As the violin has no frets to stop the strings, as is usual with the guitar, the player must know exactly where to place the fingers on the strings to play with good intonation (tuning). Beginning violinists play open strings and the lowest position, nearest to the nut. Students often start with relatively easy keys, such as A Major and G major. Students are taught scales and simple melodies. Through practice of scales and arpeggios and ear training, the violinist's left


title: Violin content: hand eventually "finds" the notes intuitively by muscle memory. Beginners sometimes rely on tapes placed on the fingerboard for proper left hand finger placement, but usually abandon the tapes quickly as they advance. Another commonly used marking technique uses dots of white-out on the fingerboard, which wear off in a few weeks of regular practice. This practice, unfortunately, is used sometimes in lieu of adequate ear-training, guiding the placement of fingers by eye and not by ear. Especially in the early stages of learning to play, the so-called "ringing tones" are useful. There are nine such notes in first position,


title: Violin content: where a stopped note sounds a unison or octave with another (open) string, causing it to resonate sympathetically. Students often use these ringing tones to check the intonation of the stopped note by seeing if it is harmonious with the open string. For example, when playing the stopped pitch "A" on the G string, the violinist could play the open D string at the same time, to check the intonation of the stopped "A". If the "A" is in tune, the "A" and the open D string should produce a harmonious perfect fourth. Violins are tuned in perfect fifths, like


title: Violin content: all the orchestral strings (violin, viola, cello) except the double bass, which is tuned in perfect fourths. Each subsequent note is stopped at a pitch the player perceives as the most harmonious, "when unaccompanied, [a violinist] does not play consistently in either the tempered or the natural [just] scale, but tends on the whole to conform with the Pythagorean scale." When violinists are playing in a string quartet or a string orchestra, the strings typically "sweeten" their tuning to suit the key they are playing in. When playing with an instrument tuned to equal temperament, such as a piano, skilled


title: Violin content: violinists adjust their tuning to match the equal temperament of the piano to avoid discordant notes. The fingers are conventionally numbered 1 (index) through 4 (little finger) in music notation, such as sheet music and etude books. Especially in instructional editions of violin music, numbers over the notes may indicate which finger to use, with "0" or "O" indicating an open string. The chart to the right shows the arrangement of notes reachable in first position. Not shown on this chart is the way the spacing between note positions becomes closer as the fingers move up (in pitch) from the


title: Violin content: nut. The bars at the sides of the chart represent the usual possibilities for beginners' tape placements, at 1st, high 2nd, 3rd, and 4th fingers. The placement of the left hand on the fingerboard is characterized by "positions". First position, where most beginners start (although some methods start in third position), is the most commonly used position in string music. Music composed for beginning youth orchestras is often mostly in first position. The lowest note available in this position in standard tuning is an open G; the highest note in first position is played with the fourth finger on the


title: Violin content: E-string, sounding a B. Moving the hand up the neck, so the first finger takes the place of the second finger, brings the player into "second position". Letting the first finger take the first-position place of the third finger brings the player to "third position", and so on. A change of positions, with its associated movement of the hand, is referred to as a "shift," and effective shifting maintaining accurate intonation and a smooth legato (connected) sound is a key element of technique at all levels. Often a "guide finger" is used; the last finger to play a note in


title: Violin content: the old position continuously lightly touches the string during the course of the shift to end up on its correct place in the new position. In elementary shifting exercises the "guide finger" is often voiced while it glides up and down the string, so the player can establish by ear whether they are landing in the correct place, however outside of these exercises it should rarely be audible (unless the performer is consciously applying a portamento effect for expressive reasons). In the course of a shift in low positions, the thumb of the left hand moves up or down the


title: Violin content: neck of the instrument so as to remain in the same position relative to the fingers (though the movement of the thumb may occur slightly before, or slightly after, the movement of the fingers). In such positions, the thumb is often thought of as an 'anchor' whose location defines what position the player is in. In very high positions, the thumb is unable to move with the fingers as the body of the instrument gets in the way. Instead, the thumb works around the neck of the instrument to sit at the point at which the neck meets the right


title: Violin content: bout of the body, and remains there while the fingers move between the high positions. A note played outside of the normal compass of a position, without any shift, is referred to as an "extension". For instance, in third position on the A string, the hand naturally sits with the first finger on D and the fourth on either G or G. Stretching the first finger back down to a C, or the fourth finger up to an A, forms an extension. Extensions are commonly used where one or two notes are slightly out of an otherwise solid position, and


title: Violin content: give the benefit of being less intrusive than a shift or string crossing. The lowest position on the violin is referred to as "half position". In this position the first finger is on a "low first position" note, e.g. B on the A string, and the fourth finger is in a downward extension from its regular position, e.g. D on the A string, with the other two fingers placed in between as required. As the position of the thumb is typically the same in "half position" as in first position, it is better thought of as a backwards extension of


title: Violin content: the whole hand than as a genuine position. The upper limit of the violin's range is largely determined by the skill of the player, who may easily play more than two octaves on a single string, and four octaves on the instrument as a whole. Position names are mostly used for the lower positions and in method books and etudes; for this reason, it is uncommon to hear references to anything higher than seventh position. The highest position, practically speaking, is 13th position. Very high positions are a particular technical challenge, for two reasons. Firstly, the difference in location of


title: Violin content: different notes becomes much narrower in high positions, making the notes more challenging to locate and in some cases to distinguish by ear. Secondly, the much shorter sounding length of the string in very high positions is a challenge for the right arm and bow in sounding the instrument effectively. The finer (and more expensive) an instrument, the better able it is to sustain good tone right to the top of the fingerboard, at the highest pitches on the E string. All notes (except those below the open D) can be played on more than one string. This is a


title: Violin content: standard design feature of stringed instruments; however, it differs from the piano, which has only one location for each of its 88 notes. For instance, the note of open A on the violin can be played as the open A, or on the D string (in first to fourth positions) or even on the G string (very high up in sixth to ninth positions). Each string has a different tone quality, because of the different weights (thicknesses) of the strings and because of the resonances of other open strings. For instance, the G string is often regarded as having a


title: Violin content: very full, sonorous sound which is particularly appropriate to late Romantic music. This is often indicated in the music by the marking, for example, "sul G" or "IV" (a Roman numeral indicating to play on the fourth string; by convention, the strings are numbered from thinnest, highest pitch (I) to the lowest pitch (IV). Even without an explicit instructions in the score, an advanced violinist will use her/his discretion and artistic sensibility to select which string to play specific notes or passages. If a string is bowed or plucked without any finger stopping it, it is said to be an


title: Violin content: "open string". This gives a different sound from a stopped string, since the string vibrates more freely at the nut than under a finger. Further, it is impossible to use vibrato fully on an open string (though a partial effect can be achieved by stopping a note an octave up on an adjacent string and vibrating that, which introduces an element of vibrato into the overtones). In the classical tradition, violinists will often use a string crossing or shift of position to allow them to avoid the change of timbre introduced by an open string. This is particularly true for


title: Violin content: the open E which is often regarded as having a harsh sound. However, there are also situations where an open string may be specifically chosen for artistic effect (particularly in modern music), in classical music which is imitating the drone of an organ (J. S. Bach, in his Partita in E for solo violin, achieved this), fiddling (e.g., "Hoedown") or where taking steps to avoid the open string is musically inappropriate (for instance in Baroque music where shifting position was less common). In quick passages of scales or arpeggios an open E string may simply be used for convenience if


title: Violin content: the note does not have time to ring and develop a harsh timbre. In folk music, fiddling and other traditional music genres, open strings are commonly used for their resonant timbre. Playing an open string simultaneously with a stopped note on an adjacent string produces a bagpipe-like drone, often used by composers in imitation of folk music. Sometimes the two notes are identical (for instance, playing a fingered A on the D string against the open A string), giving a ringing sort of "fiddling" sound. Playing an open string simultaneously with an identical stopped note can also be called for


title: Violin content: when more volume is required, especially in orchestral playing. Some classical violin parts have notes for which the composer requests the violinist to play an open string, because of the specific sonority created by an open string. Double stopping is when two separate strings are stopped by the fingers, and bowed simultaneously, producing a sixth, third, fifth, etc. harmony. Double-stops can be indicated in any position, though the widest interval that can be double-stopped naturally in one position is an octave (with the first finger on the lower string and the fourth finger on the higher string). Nonetheless, intervals of


title: Violin content: tenths or even more are sometimes required to be double-stopped in advanced playing, resulting in a very stretched left-hand position with both fingers extended. The term "double stop" is often used to encompass sounding an open string alongside a fingered note. Where three or four more simultaneous notes are written, the violinist will typically "split" the chord, choosing the lower one or two notes to play first before promptly continuing onto the upper one or two notes. A "triple stop" with three simultaneous notes is possible in some circumstances. The bow will not naturally strike three strings at once, but


title: Violin content: if there is sufficient pressure in the bowstroke the middle string can be bent down temporarily so all three can sound. This is accomplished with a heavy stroke, typically quite near the heel, and quite loud. Double stops in orchestra are divided between the players if they are not at ease with them, with half of the musicians playing the lower note and the other half playing the higher note. Sometimes, the composer will write "divisi" when he intends the two lines to be played separately. Playing double stops is common when the violins do accompaniement and another instrument plays


title: Violin content: the melody. In some Baroque music neither split-chord nor triple-stop is appropriate and violinists will arpeggiate all chords (and even what appear to be regular double stops), playing all notes individually as if they had been written as a slurred figure. In some musical styles, a sustained open string drone can be played during a passage mainly written on an adjacent string, to provide a basic accompaniment. This is more often seen in folk traditions than in classical music. However, in Baroque violins, triple-stopping came more naturally due to the bridge being less curved, so it could be played that


title: Violin content: way. Vibrato is a technique of the left hand and arm in which the pitch of a note varies subtly in a pulsating rhythm. While various parts of the hand or arm may be involved in the motion, the end result is a movement of the fingertip bringing about a slight change in vibrating string length, which causes an undulation in pitch. Some violinists oscillate backwards, or lower in pitch from the actual note when using vibrato, since it is believed that perception favors the highest pitch in a varying sound. Vibrato does little, if anything, to disguise an out-of-tune


title: Violin content: note; in other words, misapplied vibrato is a poor substitute for good intonation. Scales and other exercises meant to work on intonation are typically played without vibrato to make the work easier and more effective. Music students are often taught that unless otherwise marked in music, vibrato is assumed. However, it has to be noted that this is only a trend; there is nothing on the sheet music that compels violinists to add vibrato. This can be an obstacle to a classically trained violinist wishing to play in a style that uses little or no vibrato at all, such as


title: Violin content: baroque music played in period style and many traditional fiddling styles. Vibrato can be produced by a proper combination of finger, wrist and arm motions. One method, called "hand vibrato", involves rocking the hand back at the wrist to achieve oscillation, while another method, "arm vibrato", modulates the pitch by rocking at the elbow. A combination of these techniques allows a player to produce a large variety of tonal effects. The "when" and "what for" and "how much" of violin vibrato are artistic matters of style and taste. Different teachers, music schools and styles of music favour different vibrato styles.


title: Violin content: For example, overdone vibrato may become distracting. In acoustic terms, the interest that vibrato adds to the sound has to do with the way that the overtone mix (or tone color, or timbre) and the directional pattern of sound projection change with changes in pitch. By "pointing" the sound at different parts of the room in a rhythmic way, vibrato adds a "shimmer" or "liveliness" to the sound of a well-made violin. Vibrato is, in a large part, left to the discretion of the violinist. Different types of vibrato will bring different moods to the piece, and the varying degrees


title: Violin content: and styles of vibrato are often characteristics that stand out in well-known violinists. Vibrato can also be used for a fast trill. A trill initiated from just hammering the finger up and down on the fingerboard will create a harsher quality than with a vibrato trill. For example, if trilling on the first finger, the second finger is placed very slightly off the string and vibrato is implemented. The second finger will lightly touch the string above the first finger causing the pitch to change. This has a softer quality and many think it is nicer-sounding than a hammered trill.


title: Violin content: Note: this trill technique only works well for semi-tonal trills, it is far more difficult to vibrato trill for an interval of a tone or more. Lightly touching the string with a fingertip at a harmonic node, but without fully pressing the string, and then plucking or bowing the string, creates harmonics. Instead of the normal tone, a higher pitched note sounds. Each node is at an integer division of the string, for example half-way or one-third along the length of the string. A responsive instrument will sound numerous possible harmonic nodes along the length of the string. Harmonics are


title: Violin content: marked in music either with a little circle above the note that determines the pitch of the harmonic, or by diamond-shaped note heads. There are two types of harmonics: natural harmonics and artificial harmonics (also known as "false harmonics"). Natural harmonics are played on an open string. The pitch of the open string when it is plucked or bowed is called the fundamental frequency. Harmonics are also called "overtones" or "partials". They occur at whole-number multiples of the fundamental, which is called the first harmonic. The second harmonic is the first overtone (the octave above the open string), the third


title: Violin content: harmonic is the second overtone, and so on. The second harmonic is in the middle of the string and sounds an octave higher than the string's pitch. The third harmonic breaks the string into thirds and sounds an octave and a fifth above the fundamental, and the fourth harmonic breaks the string into quarters sounding two octaves above the first. The sound of the second harmonic is the clearest of them all, because it is a common node with all the succeeding even-numbered harmonics (4th, 6th, etc.). The third and succeeding odd-numbered harmonics are harder to play because they break


title: Violin content: the string into an odd number of vibrating parts and do not share as many nodes with other harmonics. Artificial harmonics are more difficult to produce than natural harmonics, as they involve both stopping the string and playing a harmonic on the stopped note. Using the "octave frame" (the normal distance between the first and fourth fingers in any given position) with the fourth finger just touching the string a fourth higher than the stopped note produces the fourth harmonic, two octaves above the stopped note. Finger placement and pressure, as well as bow speed, pressure, and sounding point are


title: Violin content: all essential in getting the desired harmonic to sound. And to add to the challenge, in passages with different notes played as false harmonics, the distance between stopping finger and harmonic finger must constantly change, since the spacing between notes changes along the length of the string. The "harmonic finger" can also touch at a major third above the pressed note (the fifth harmonic), or a fifth higher (a third harmonic). These harmonics are less commonly used; in the case of the major third, both the stopped note and touched note must be played slightly sharp otherwise the harmonic does


title: Violin content: not speak as readily. In the case of the fifth, the stretch is greater than is comfortable for many violinists. In the general repertoire fractions smaller than a sixth are not used. However, divisions up to an eighth are sometimes used and, given a good instrument and a skilled player, divisions as small as a twelfth are possible. There are a few books dedicated solely to the study of violin harmonics. Two comprehensive works are Henryk Heller's seven-volume "Theory of Harmonics", published by Simrock in 1928, and Michelangelo Abbado's five-volume "Tecnica dei suoni armonici" published by Ricordi in 1934. Elaborate


title: Violin content: passages in artificial harmonics can be found in virtuoso violin literature, especially of the 19th and early 20th centuries. Two notable examples of this are an entire section of Vittorio Monti's "Csárdás" and a passage towards the middle of the third movement of Pyotr Ilyich Tchaikovsky's Violin Concerto. A section of the third movement of Violin Concerto No. 1 (Paganini) consists of double-stopped thirds in harmonics. When strings are worn, dirty and old, the harmonics may no longer be accurate in pitch. For this reason, violinists change their strings regularly. The strings may be sounded by drawing the hair of


title: Violin content: the bow held by the right hand across them ("arco") or by plucking them ("pizzicato") most often with the right hand. In some cases, the violinist will pluck strings with the left hand. This is done to facilitate transitions from pizz to arco playing. It is also used in some virtuoso showpieces. Left hand pizzes are usually open strings. Pizz is used on all of the violin family instruments; however, the systematic study of advanced pizzicato techniques is most developed in jazz bass, a style in which the instrument is mostly played pizzicato. The right arm, hand, and bow and


title: Violin content: the bow speed are responsible for tone quality, rhythm, dynamics, articulation, and most (but not all) changes in timbre. The player draws the bow over the string, causing the string to vibrate and produce a sustained tone. The bow is a wooden stick with tensioned horsetail hair, which has been rosined with a bar of rosin. The natural texture of the horsehair and the stickiness of the rosin help the bow to "grip" the string, and thus when the bow is drawn over the string, the bow causes the string to sound a pitch. Bowing can be used to produce


title: Violin content: long sustained notes or melodies. With a string section, if the players in a section change their bows at different times, a note can seem to be endlessly sustainable. As well, the bow can be used to play short, crisp little notes, such as repeated notes, scales and arpeggios, which provide a propulsive rhythm in many styles of music. The most essential part of bowing technique is the bow grip. It is usually with the thumb bent in the small area between the frog and the winding of the bow. The other fingers are spread somewhat evenly across the top


title: Violin content: part of the bow. The pinky finger is curled with the tip of the finger placed on the wood next to the screw. The violin produces louder notes with greater bow speed or more weight on the string. The two methods are not equivalent, because they produce different timbres; pressing down on the string tends to produce a harsher, more intense sound. One can also achieve a louder sound by placing the bow closer to the bridge. The sounding point where the bow intersects the string also influences timbre (or "tone colour"). Playing close to the bridge ("sul ponticello") gives


title: Violin content: a more intense sound than usual, emphasizing the higher harmonics; and playing with the bow over the end of the fingerboard ("sul tasto") makes for a delicate, ethereal sound, emphasizing the fundamental frequency. Dr. Suzuki referred to the sounding point as the "Kreisler highway"; one may think of different sounding points as "lanes" in the highway. Various methods of attack with the bow produce different articulations. There are many bowing techniques that allow for every range of playing style and many teachers, players, and orchestras spend a lot of time developing techniques and creating a unified technique within the group.


title: Violin content: These techniques include legato-style bowing (a smooth, connected, sustained sound suitable for melodies), collé, and a variety of bowings which produce shorter notes, including ricochet, sautillé, martelé, spiccato, and staccato. A note marked "pizz." (abbreviation for "pizzicato") in the written music is to be played by plucking the string with a finger of the right hand rather than by bowing. (The index finger is most commonly used here.) Sometimes in orchestra parts or virtuoso solo music where the bow hand is occupied (or for show-off effect), "left-hand pizzicato" will be indicated by a + (plus sign) below or above the


title: Violin content: note. In left-hand pizzicato, two fingers are put on the string; one (usually the index or middle finger) is put on the correct note, and the other (usually the ring finger or little finger) is put above the note. The higher finger then plucks the string while the lower one stays on, thus producing the correct pitch. By increasing the force of the pluck, one can increase the volume of the note that the string is producing. Pizzicato is used in orchestral works and in solo showpieces. In orchestral parts, violinists often have to make very quick shifts from arco


title: Violin content: to pizzicato, and vice versa. A marking of "col legno" (Italian for "with the wood") in the written music calls for striking the string(s) with the stick of the bow, rather than by drawing the hair of the bow across the strings. This bowing technique is somewhat rarely used, and results in a muted percussive sound. The eerie quality of a violin section playing "col legno" is exploited in some symphonic pieces, notably the "Witches' Dance" of the last movement of Berlioz's Symphonie Fantastique. Saint-Saëns's symphonic poem "Danse Macabre" includes the string section using the "col legno" technique to imitate


title: Violin content: the sound of dancing skeletons. "Mars" from Gustav Holst's "The Planets" uses "col legno" to play a repeated rhythm in time signature. Benjamin Britten's "The Young Person's Guide to the Orchestra" demands its use in the "Percussion" Variation. Dmitri Shostakovich uses it in his Fourteenth Symphony in the movement 'At the Sante Jail'. Some violinists, however, object to this style of playing as it can damage the finish and impair the value of a fine bow, but most of such will compromise by using a cheap bow for at least the duration of the passage in question. Detaché A smooth


title: Violin content: and even stroke during which bow speed and weight are the same from beginning of the stroke to the end. Literally "hammered", a strongly accented effect produced by releasing each bowstroke forcefully and suddenly. Martelé can be played in any part of the bow. It is sometimes indicated in written music by an arrowhead. Tremolo is the very rapid repetition (typically of a single note, but occasionally of multiple notes), usually played at the tip of the bow. Tremolo is marked with three short, slanted lines across the stem of the note. Tremolo is often used as a sound effect


title: Violin content: in orchestral music, particularly in the Romantic music era (1800-1910) and in opera music. Attaching a small metal, rubber, leather, or wooden device called a "mute", or "sordino", to the bridge of the violin gives a softer, more mellow tone, with fewer audible overtones; the sound of an entire orchestral string section playing with mutes has a hushed quality. The mute changes both the loudness and the timbre ("tone colour") of a violin. The conventional Italian markings for mute usage are "con sord.", or "con sordino", meaning 'with mute'; and "senza sord.", meaning 'without mute'; or "via sord.", meaning 'mute


title: Violin content: off'. Larger metal, rubber, or wooden mutes are widely available, known as "practice mutes" or "hotel mutes". Such mutes are generally not used in performance, but are used to deaden the sound of the violin in practice areas such as hotel rooms. (For practicing purposes there is also the mute violin, a violin without a sound box.) Some composers have used practice mutes for special effect, for example, at the end of Luciano Berio's "Sequenza VIII" for solo violin. Since the Baroque era, the violin has been one of the most important of all instruments in classical music, for several


title: Violin content: reasons. The tone of the violin stands out above other instruments, making it appropriate for playing a melody line. In the hands of a good player, the violin is extremely agile, and can execute rapid and difficult sequences of notes. Violins make up a large part of an orchestra, and are usually divided into two sections, known as the first and second violins. Composers often assign the melody to the first violins, typically a more difficult part using higher positions, while second violins play harmony, accompaniment patterns or the melody an octave lower than the first violins. A string quartet


title: Violin content: similarly has parts for first and second violins, as well as a viola part, and a bass instrument, such as the cello or, rarely, the double bass. The earliest references to jazz performance using the violin as a solo instrument are documented during the first decades of the 20th century. Joe Venuti, one of the first jazz violinists, is known for his work with guitarist Eddie Lang during the 1920s. Since that time there have been many improvising violinists including Stéphane Grappelli, Stuff Smith, Eddie South, Regina Carter, Johnny Frigo, John Blake, Adam Taubitz, Leroy Jenkins, and Jean-Luc Ponty. While


title: Violin content: not primarily jazz violinists, Darol Anger and Mark O'Connor have spent significant parts of their careers playing jazz. The Swiss-Cuban violinist Yilian Cañizares mixes jazz with Cuban music. Violins also appear in ensembles supplying orchestral backgrounds to many jazz recordings. The Indian violin, while essentially the same instrument as that used in Western music, is different in some senses. The instrument is tuned so that the IV and III strings (G and D on a western-tuned violin) and the II and I (A and E) strings are sa–pa (do–sol) pairs and sound the same but are offset by an octave,


title: Violin content: resembling common scordatura or fiddle cross-tunings such as G–D–G–D or A–E–A–E. The tonic sa (do) is not fixed, but variably tuned to accommodate the vocalist or lead player. The way the musician holds the instrument varies from Western to Indian music. In Indian music the musician sits on the floor cross-legged with the right foot out in front of them. The scroll of the instrument rests on the foot. This position is essential to playing well due to the nature of Indian music. The hand can move all over the fingerboard and there is no set position for the left


title: Violin content: hand, so it is important for the violin to be in a steady, unmoving position. Up through at least the 1970s, most types of popular music used bowed string sections. They were extensively used in popular music throughout the 1920s and early 1930s. With the rise of swing music, however, from 1935 to 1945, the string sound was often used to add to the fullness of big band music. Following the swing era, from the late 1940s to the mid-1950s, strings began to be revived in traditional pop music. This trend accelerated in the late 1960s, with a significant revival


title: Violin content: of the use of strings, especially in soul music. Popular Motown recordings of the late 1960s and 1970s relied heavily on strings as part of their trademark texture. The rise of disco music in the 1970s continued this trend with the heavy use of string instruments in popular disco orchestras (e.g., Love Unlimited Orchestra, Biddu Orchestra, Monster Orchestra, Salsoul Orchestra, MFSB). With the rise of electronically created music in the 1980s, violins declined in use, as synthesized string sounds played by a keyboardist with a synthesizer took their place. However, while the violin has had very little usage in mainstream


title: Violin content: rock music, it has some history in progressive rock (e.g., Electric Light Orchestra, King Crimson, Kansas, Gentle Giant). The 1973 album "" by Italy's RDM plays violins off against synthesizers at its finale ("La grande fuga"). The instrument has a stronger place in modern jazz fusion bands, notably The Corrs. The fiddle is sometimes a part of British folk rock music, as exemplified by the likes of Fairport Convention and Steeleye Span. The popularity of crossover music beginning in the last years of the 20th century has brought the violin back into the popular music arena, with both electric and


title: Violin content: acoustic violins being used by popular bands. Dave Matthews Band features violinist Boyd Tinsley. The Flock featured violinist Jerry Goodman who later joined the jazz-rock fusion band, The Mahavishnu Orchestra. James' Saul Davies, who is also a guitarist, was enlisted by the band as a violinist. For their first three albums and related singles, the British group No-Man made extensive use of electric and acoustic solo violin as played by band member Ben Coleman (who played violin exclusively). Pop-Punk band Yellowcard has made a mainstay of violin in its music. Violinist Sean Mackin has been a member of the band


title: Violin content: since 1997. Los Salvadores also combine punk and ska influences with a violin. Doom metal band My Dying Bride have used violin as a part of their line-up throughout many of their albums. The violin appears prominently in the music of Spanish folk metal group Mägo de Oz (for example, in their 1998 hit "Molinos de viento"). The violinist (Carlos Prieto a.k.a. "Mohamed") has been one of the group's most popular members with fans since 1992. The instrument is also used often in symphonic metal, particularly by bands such as Therion, Nightwish, Within Temptation, Haggard, and Epica, although it can


title: Violin content: also be found in Gothic Metal bands such as Tristania and Theater of Tragedy. The alternative rock band Hurt's vocalist plays violin for the band, making them one of few rock bands to feature violin without hiring a session worker. The folk metal band Ithilien use violin extensively along their discography. Progressive metal band Ne Obliviscaris feature a violin player, Tim Charles, in their line-up. Independent artists, such as Owen Pallett, The Shondes, and Andrew Bird, have also spurred increased interest in the instrument. Indie bands have often embraced new and unusual arrangements, allowing them more freedom to feature the


title: Violin content: violin than many mainstream musical artists. It has been used in the post-rock genre by bands such as A Genuine Freakshow, Sigur Rós, Zox, Broken Social Scene, and A Silver Mt. Zion. The electric violin has even been used by bands like The Crüxshadows within the context of keyboard based music. Lindsey Stirling plays the violin in conjunction with electronic/dubstep/trance rifts and beats. Eric Stanley improvises on the violin with hip hop music/pop/classical elements and instrumental beats. The successful indie rock and baroque pop band Arcade Fire use violins extensively in their arrangements. Indian, Pakistani, Turkish, and Arabic pop music


title: Violin content: is filled with the sound of violins, both soloists and ensembles. Like many other instruments used in classical music, the violin descends from remote ancestors that were used for folk music. Following a stage of intensive development in the late Renaissance, largely in Italy, the violin had improved (in volume, tone, and agility), to the point that it not only became a very important instrument in art music, but proved highly appealing to folk musicians as well, ultimately spreading very widely, sometimes displacing earlier bowed instruments. Ethnomusicologists have observed its widespread use in Europe, Asia, and the Americas. When played


title: Violin content: as a folk instrument, the violin is usually referred to in English as a "fiddle" (although the term "fiddle" can be used informally no matter what the genre of music). Worldwide, there are various stringed instruments such as the wheel fiddle and Apache fiddle that are also called "fiddles". Fiddle music differs from classical in that the tunes are generally considered dance music, and various techniques, such as droning, shuffling, and ornamentation specific to particular styles are used. In many traditions of folk music, the tunes are not written but are memorized by successive generations of musicians and passed on


title: Violin content: in what is known as the oral tradition. Many old-time pieces call for cross-tuning, or using tunings other than standard GDAE. Some players of American styles of folk fiddling (such as bluegrass or old-time) have their bridge's top edge cut to a slightly flatter curve, making techniques such as a "double shuffle" less taxing on the bow arm, as it reduces the range of motion needed for alternating between double stops on different string pairs. Fiddlers who use solid steel core strings may prefer to use a tailpiece with fine tuners on all four strings, instead of the single fine


title: Violin content: tuner on the E string used by many classical players. As well as the Arabic rababah, the violin has been used in Arabic music. Electric violins have a magnetic or piezoelectric pickup that converts string vibration to an electric signal. A patch cable or wireless transmitter sends the signal to an amplifier of a PA system. Electric violins are usually constructed as such, but a pickup can be added to a conventional acoustic violin. An electric violin with a resonating body that produces listening-level sound independently of the electric elements can be called an "electro-acoustic violin". To be effective as


title: Violin content: an acoustic violin, electro-acoustic violins retain much of the resonating body of the violin, and often resemble an acoustic violin or fiddle. The body may be finished in bright colors and made from alternative materials to wood. These violins may need to be hooked up to an instrument amplifier or PA system. Some types come with a silent option that allows the player to use headphones that are hooked up to the violin. The first specially built electric violins date back to 1928 and were made by Victor Pfeil, Oskar Vierling, George Eisenberg, Benjamin Miessner, George Beauchamp, Hugo Benioff and


title: Violin content: Fredray Kislingbury. These violins can be plugged into effect units, just like an electric guitar, including distortion, wah-wah pedal and reverb. Since electric violins do not rely on string tension and resonance to amplify their sound they can have more strings. For example, five-stringed electric violins are available from several manufacturers, and a seven string electric violin (with three lower strings encompassing the cello's range) is also available. The majority of the first electric violinists were musicians playing jazz fusion (e.g., Jean-Luc Ponty) and popular music. Violin authentication is the process of determining the maker and manufacture date of a


title: Violin content: violin. This process is similar to that used to determine the provenance of art works. As significant value may be attached to violins made either by specific makers or at specific times and locations, forgery and other methods of fraudulent misrepresentation can be used to inflate the value of an instrument. Violin The violin, also known informally as a fiddle, is a wooden string instrument in the violin family. Most violins have a hollow wooden body. It is the smallest and highest-pitched instrument in the family in regular use. Smaller violin-type instruments are known, including the violino piccolo and the


title: "Vladimir Arnold" content: worked at the Steklov Mathematical Institute in Moscow and at Paris Dauphine University up until his death. he was reported to have the highest citation index among Russian scientists, and h-index of 40. To his students and colleagues Arnold was known also for his sense of humour. For example, once at his seminar in Moscow, at the beginning of the school year, when he usually was formulating new problems, he said: Arnold died of acute pancreatitis on 3 June 2010 in Paris, nine days before his 73rd birthday. His students include Alexander Givental, Victor Goryunov, Sabir Gusein-Zade, Emil Horozov, Boris


title: Vacuum content: Vacuum Vacuum is space devoid of matter. The word stems from the Latin adjective "vacuus" for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often discuss ideal test results that would occur in a "perfect" vacuum, which they sometimes simply call "vacuum" or free space, and use the term partial vacuum to refer to an actual imperfect vacuum as one might have in a laboratory or in space. In engineering and applied physics on the other hand, vacuum refers to any space in which the pressure is


title: Vacuum content: lower than atmospheric pressure. The Latin term in vacuo is used to describe an object that is surrounded by a vacuum. The "quality" of a partial vacuum refers to how closely it approaches a perfect vacuum. Other things equal, lower gas pressure means higher-quality vacuum. For example, a typical vacuum cleaner produces enough suction to reduce air pressure by around 20%. Much higher-quality vacuums are possible. Ultra-high vacuum chambers, common in chemistry, physics, and engineering, operate below one trillionth (10) of atmospheric pressure (100 nPa), and can reach around 100 particles/cm. Outer space is an even higher-quality vacuum, with the


title: Vacuum content: equivalent of just a few hydrogen atoms per cubic meter on average in intergalactic space. According to modern understanding, even if all matter could be removed from a volume, it would still not be "empty" due to vacuum fluctuations, dark energy, transiting gamma rays, cosmic rays, neutrinos, and other phenomena in quantum physics. In the study of electromagnetism in the 19th century, vacuum was thought to be filled with a medium called aether. In modern particle physics, the vacuum state is considered the ground state of a field. Vacuum has been a frequent topic of philosophical debate since ancient Greek


title: Vacuum content: times, but was not studied empirically until the 17th century. Evangelista Torricelli produced the first laboratory vacuum in 1643, and other experimental techniques were developed as a result of his theories of atmospheric pressure. A torricellian vacuum is created by filling a tall glass container closed at one end with mercury, and then inverting it in a bowl to contain the mercury (see below). Vacuum became a valuable industrial tool in the 20th century with the introduction of incandescent light bulbs and vacuum tubes, and a wide array of vacuum technology has since become available. The recent development of human


title: Vacuum content: spaceflight has raised interest in the impact of vacuum on human health, and on life forms in general. The word "vacuum" comes , noun use of neuter of "vacuus", meaning "empty", related to "vacare", meaning "be empty". "Vacuum" is one of the few words in the English language that contains two consecutive letters '"u"'. Historically, there has been much dispute over whether such a thing as a vacuum can exist. Ancient Greek philosophers debated the existence of a vacuum, or void, in the context of atomism, which posited void and atom as the fundamental explanatory elements of physics. Following Plato,


title: Vacuum content: even the abstract concept of a featureless void faced considerable skepticism: it could not be apprehended by the senses, it could not, itself, provide additional explanatory power beyond the physical volume with which it was commensurate and, by definition, it was quite literally nothing at all, which cannot rightly be said to exist. Aristotle believed that no void could occur naturally, because the denser surrounding material continuum would immediately fill any incipient rarity that might give rise to a void. In his "Physics", book IV, Aristotle offered numerous arguments against the void: for example, that motion through a medium which


title: Vacuum content: offered no impediment could continue "ad infinitum", there being no reason that something would come to rest anywhere in particular. Although Lucretius argued for the existence of vacuum in the first century BC and Hero of Alexandria tried unsuccessfully to create an artificial vacuum in the first century AD, it was European scholars such as Roger Bacon, Blasius of Parma and Walter Burley in the 13th and 14th century who focused considerable attention on these issues. Eventually following Stoic physics in this instance, scholars from the 14th century onward increasingly departed from the Aristotelian perspective in favor of a supernatural


title: Vacuum content: void beyond the confines of the cosmos itself, a conclusion widely acknowledged by the 17th century, which helped to segregate natural and theological concerns. Almost two thousand years after Plato, René Descartes also proposed a geometrically based alternative theory of atomism, without the problematic nothing–everything dichotomy of void and atom. Although Descartes agreed with the contemporary position, that a vacuum does not occur in nature, the success of his namesake coordinate system and more implicitly, the spatial–corporeal component of his metaphysics would come to define the philosophically modern notion of empty space as a quantified extension of volume. By the


title: Vacuum content: ancient definition however, directional information and magnitude were conceptually distinct. In the medieval Middle Eastern world, the physicist and Islamic scholar, Al-Farabi (Alpharabius, 872–950), conducted a small experiment concerning the existence of vacuum, in which he investigated handheld plungers in water. He concluded that air's volume can expand to fill available space, and he suggested that the concept of perfect vacuum was incoherent. However, according to Nader El-Bizri, the physicist Ibn al-Haytham (Alhazen, 965–1039) and the Mu'tazili theologians disagreed with Aristotle and Al-Farabi, and they supported the existence of a void. Using geometry, Ibn al-Haytham mathematically demonstrated that place ("al-makan")


title: Vacuum content: is the imagined three-dimensional void between the inner surfaces of a containing body. According to Ahmad Dallal, Abū Rayhān al-Bīrūnī also states that "there is no observable evidence that rules out the possibility of vacuum". The suction pump later appeared in Europe from the 15th century. Medieval thought experiments into the idea of a vacuum considered whether a vacuum was present, if only for an instant, between two flat plates when they were rapidly separated. There was much discussion of whether the air moved in quickly enough as the plates were separated, or, as Walter Burley postulated, whether a 'celestial


title: Vacuum content: agent' prevented the vacuum arising. The commonly held view that nature abhorred a vacuum was called "horror vacui". Speculation that even God could not create a vacuum if he wanted to was shut down by the 1277 Paris condemnations of Bishop Etienne Tempier, which required there to be no restrictions on the powers of God, which led to the conclusion that God could create a vacuum if he so wished. Jean Buridan reported in the 14th century that teams of ten horses could not pull open bellows when the port was sealed. The 17th century saw the first attempts to


title: Vacuum content: quantify measurements of partial vacuum. Evangelista Torricelli's mercury barometer of 1643 and Blaise Pascal's experiments both demonstrated a partial vacuum. In 1654, Otto von Guericke invented the first vacuum pump and conducted his famous Magdeburg hemispheres experiment, showing that teams of horses could not separate two hemispheres from which the air had been partially evacuated. Robert Boyle improved Guericke's design and with the help of Robert Hooke further developed vacuum pump technology. Thereafter, research into the partial vacuum lapsed until 1850 when August Toepler invented the Toepler Pump and Heinrich Geissler invented the mercury displacement pump in 1855, achieving a


title: Vacuum content: partial vacuum of about 10 Pa (0.1 Torr). A number of electrical properties become observable at this vacuum level, which renewed interest in further research. While outer space provides the most rarefied example of a naturally occurring partial vacuum, the heavens were originally thought to be seamlessly filled by a rigid indestructible material called aether. Borrowing somewhat from the pneuma of Stoic physics, aether came to be regarded as the rarefied air from which it took its name, (see Aether (mythology)). Early theories of light posited a ubiquitous terrestrial and celestial medium through which light propagated. Additionally, the concept informed


title: Vacuum content: Isaac Newton's explanations of both refraction and of radiant heat. 19th century experiments into this luminiferous aether attempted to detect a minute drag on the Earth's orbit. While the Earth does, in fact, move through a relatively dense medium in comparison to that of interstellar space, the drag is so minuscule that it could not be detected. In 1912, astronomer Henry Pickering commented: "While the interstellar absorbing medium may be simply the ether, [it] is characteristic of a gas, and free gaseous molecules are certainly there". Later, in 1930, Paul Dirac proposed a model of the vacuum as an infinite


title: Vacuum content: sea of particles possessing negative energy, called the Dirac sea. This theory helped refine the predictions of his earlier formulated Dirac equation, and successfully predicted the existence of the positron, confirmed two years later. Werner Heisenberg's uncertainty principle formulated in 1927, predict a fundamental limit within which instantaneous position and momentum, or energy and time can be measured. This has far reaching consequences on the "emptiness" of space between particles. In the late 20th century, so-called virtual particles that arise spontaneously from empty space were confirmed. The strictest criterion to define a vacuum is a region of space and time


title: Vacuum content: where all the components of the stress–energy tensor are zero. This means that this region is devoid of energy and momentum, and by consequence, it must be empty of particles and other physical fields (such as electromagnetism) that contain energy and momentum. In general relativity, a vanishing stress-energy tensor implies, through Einstein field equations, the vanishing of all the components of the Ricci tensor. Vacuum does not mean that the curvature of space-time is necessarily flat: the gravitational field can still produce curvature in a vacuum in the form of tidal forces and gravitational waves (technically, these phenomena are the


title: Vacuum content: components of the Weyl tensor). The black hole (with zero electric charge) is an elegant example of a region completely "filled" with vacuum, but still showing a strong curvature. In classical electromagnetism, the vacuum of free space, or sometimes just "free space" or "perfect vacuum", is a standard reference medium for electromagnetic effects. Some authors refer to this reference medium as "classical vacuum", a terminology intended to separate this concept from QED vacuum or QCD vacuum, where vacuum fluctuations can produce transient virtual particle densities and a relative permittivity and relative permeability that are not identically unity. In the theory


title: Vacuum content: of classical electromagnetism, free space has the following properties: The vacuum of classical electromagnetism can be viewed as an idealized electromagnetic medium with the constitutive relations in SI units: relating the electric displacement field D to the electric field E and the magnetic field or "H"-field H to the magnetic induction or "B"-field B. Here r is a spatial location and "t" is time. In quantum mechanics and quantum field theory, the vacuum is defined as the state (that is, the solution to the equations of the theory) with the lowest possible energy (the ground state of the Hilbert space).


title: Vacuum content: In quantum electrodynamics this vacuum is referred to as 'QED vacuum' to distinguish it from the vacuum of quantum chromodynamics, denoted as QCD vacuum. QED vacuum is a state with no matter particles (hence the name), and also no photons. As described above, this state is impossible to achieve experimentally. (Even if every matter particle could somehow be removed from a volume, it would be impossible to eliminate all the blackbody photons.) Nonetheless, it provides a good model for realizable vacuum, and agrees with a number of experimental observations as described next. QED vacuum has interesting and complex properties. In


title: Vacuum content: QED vacuum, the electric and magnetic fields have zero average values, but their variances are not zero. As a result, QED vacuum contains vacuum fluctuations (virtual particles that hop into and out of existence), and a finite energy called vacuum energy. Vacuum fluctuations are an essential and ubiquitous part of quantum field theory. Some experimentally verified effects of vacuum fluctuations include spontaneous emission and the Lamb shift. Coulomb's law and the electric potential in vacuum near an electric charge are modified. Theoretically, in QCD multiple vacuum states can coexist. The starting and ending of cosmological inflation is thought to have


title: Vacuum content: arisen from transitions between different vacuum states. For theories obtained by quantization of a classical theory, each stationary point of the energy in the configuration space gives rise to a single vacuum. String theory is believed to have a huge number of vacua – the so-called string theory landscape. Outer space has very low density and pressure, and is the closest physical approximation of a perfect vacuum. But no vacuum is truly perfect, not even in interstellar space, where there are still a few hydrogen atoms per cubic meter. Stars, planets, and moons keep their atmospheres by gravitational attraction, and


title: Vacuum content: as such, atmospheres have no clearly delineated boundary: the density of atmospheric gas simply decreases with distance from the object. The Earth's atmospheric pressure drops to about at of altitude, the Kármán line, which is a common definition of the boundary with outer space. Beyond this line, isotropic gas pressure rapidly becomes insignificant when compared to radiation pressure from the Sun and the dynamic pressure of the solar winds, so the definition of pressure becomes difficult to interpret. The thermosphere in this range has large gradients of pressure, temperature and composition, and varies greatly due to space weather. Astrophysicists prefer


title: Vacuum content: to use number density to describe these environments, in units of particles per cubic centimetre. But although it meets the definition of outer space, the atmospheric density within the first few hundred kilometers above the Kármán line is still sufficient to produce significant drag on satellites. Most artificial satellites operate in this region called low Earth orbit and must fire their engines every few days to maintain orbit. The drag here is low enough that it could theoretically be overcome by radiation pressure on solar sails, a proposed propulsion system for interplanetary travel. Planets are too massive for their trajectories


title: Vacuum content: to be significantly affected by these forces, although their atmospheres are eroded by the solar winds. All of the observable universe is filled with large numbers of photons, the so-called cosmic background radiation, and quite likely a correspondingly large number of neutrinos. The current temperature of this radiation is about 3 K, or −270 degrees Celsius or −454 degrees Fahrenheit. The quality of a vacuum is indicated by the amount of matter remaining in the system, so that a high quality vacuum is one with very little matter left in it. Vacuum is primarily measured by its absolute pressure, but


title: Vacuum content: a complete characterization requires further parameters, such as temperature and chemical composition. One of the most important parameters is the mean free path (MFP) of residual gases, which indicates the average distance that molecules will travel between collisions with each other. As the gas density decreases, the MFP increases, and when the MFP is longer than the chamber, pump, spacecraft, or other objects present, the continuum assumptions of fluid mechanics do not apply. This vacuum state is called "high vacuum", and the study of fluid flows in this regime is called particle gas dynamics. The MFP of air at atmospheric


title: Vacuum content: pressure is very short, 70 nm, but at 100 mPa (~) the MFP of room temperature air is roughly 100 mm, which is on the order of everyday objects such as vacuum tubes. The Crookes radiometer turns when the MFP is larger than the size of the vanes. Vacuum quality is subdivided into ranges according to the technology required to achieve it or measure it. These ranges do not have universally agreed definitions, but a typical distribution is shown in the following table. As we travel into orbit, outer space and ultimately intergalactic space, the pressure varies by several orders


title: Vacuum content: of magnitude. Vacuum is measured in units of pressure, typically as a subtraction relative to ambient atmospheric pressure on Earth. But the amount of relative measurable vacuum varies with local conditions. On the surface of Jupiter, where ground level atmospheric pressure is much higher than on Earth, much higher relative vacuum readings would be possible. On the surface of the moon with almost no atmosphere, it would be extremely difficult to create a measurable vacuum relative to the local environment. Similarly, much higher than normal relative vacuum readings are possible deep in the Earth's ocean. A submarine maintaining an internal


title: Vacuum content: pressure of 1 atmosphere submerged to a depth of 10 atmospheres (98 metres; a 9.8 metre column of seawater has the equivalent weight of 1 atm) is effectively a vacuum chamber keeping out the crushing exterior water pressures, though the 1 atm inside the submarine would not normally be considered a vacuum. Therefore, to properly understand the following discussions of vacuum measurement, it is important that the reader assumes the relative measurements are being done on Earth at sea level, at exactly 1 atmosphere of ambient atmospheric pressure. The SI unit of pressure is the pascal (symbol Pa), but vacuum


title: Vacuum content: is often measured in torrs, named for Torricelli, an early Italian physicist (1608–1647). A torr is equal to the displacement of a millimeter of mercury (mmHg) in a manometer with 1 torr equaling 133.3223684 pascals above absolute zero pressure. Vacuum is often also measured on the barometric scale or as a percentage of atmospheric pressure in bars or atmospheres. Low vacuum is often measured in millimeters of mercury (mmHg) or pascals (Pa) below standard atmospheric pressure. "Below atmospheric" means that the absolute pressure is equal to the current atmospheric pressure. In other words, most low vacuum gauges that read, for


title: Vacuum content: example 50.79 Torr. Many inexpensive low vacuum gauges have a margin of error and may report a vacuum of 0 Torr but in practice this generally requires a two-stage rotary vane or other medium type of vacuum pump to go much beyond (lower than) 1 torr. Many devices are used to measure the pressure in a vacuum, depending on what range of vacuum is needed. Hydrostatic gauges (such as the mercury column manometer) consist of a vertical column of liquid in a tube whose ends are exposed to different pressures. The column will rise or fall until its weight is


title: Vacuum content: in equilibrium with the pressure differential between the two ends of the tube. The simplest design is a closed-end U-shaped tube, one side of which is connected to the region of interest. Any fluid can be used, but mercury is preferred for its high density and low vapour pressure. Simple hydrostatic gauges can measure pressures ranging from 1 torr (100 Pa) to above atmospheric. An important variation is the McLeod gauge which isolates a known volume of vacuum and compresses it to multiply the height variation of the liquid column. The McLeod gauge can measure vacuums as high as 10


title: Vacuum content: torr (0.1 mPa), which is the lowest direct measurement of pressure that is possible with current technology. Other vacuum gauges can measure lower pressures, but only indirectly by measurement of other pressure-controlled properties. These indirect measurements must be calibrated via a direct measurement, most commonly a McLeod gauge. The kenotometer is a particular type of hydrostatic gauge, typically used in power plants using steam turbines. The kenotometer measures the vacuum in the steam space of the condenser, that is, the exhaust of the last stage of the turbine. Mechanical or elastic gauges depend on a Bourdon tube, diaphragm, or capsule,


title: Vacuum content: usually made of metal, which will change shape in response to the pressure of the region in question. A variation on this idea is the capacitance manometer, in which the diaphragm makes up a part of a capacitor. A change in pressure leads to the flexure of the diaphragm, which results in a change in capacitance. These gauges are effective from 10 torr to 10 torr, and beyond. Thermal conductivity gauges rely on the fact that the ability of a gas to conduct heat decreases with pressure. In this type of gauge, a wire filament is heated by running current


title: Vacuum content: through it. A thermocouple or Resistance Temperature Detector (RTD) can then be used to measure the temperature of the filament. This temperature is dependent on the rate at which the filament loses heat to the surrounding gas, and therefore on the thermal conductivity. A common variant is the Pirani gauge which uses a single platinum filament as both the heated element and RTD. These gauges are accurate from 10 torr to 10 torr, but they are sensitive to the chemical composition of the gases being measured. Ionization gauges are used in ultrahigh vacuum. They come in two types: hot cathode