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SI Derived Unit The International System of Units (SI) specifies a set of seven base units from which all other SI units of measurement are derived. These SI DERIVED UNITS are either dimensionless , or can be expressed as a product of one or more of the base units, possibly scaled by an appropriate power of exponentiation . Many derived units do not have special names. For example, the SI derived unit of area is the square metre (m2) and the SI derived unit of density is the kilogram per cubic metre (kg/m3 or kg m−3). However, 22 derived units are recognized by the SI with special names, which are written in lowercase. However, the symbols for units named after persons, are always written with an uppercase initial letter. For example, the symbol for the hertz is "Hz"; but the symbol for the metre is "m". CONTENTS * 1 Derived units with special names * 2 Examples of derived quantities and units * 3 Other units used with SI * 4 Supplementary units * 5 See also * 6 References * 7 Bibliography DERIVED UNITS WITH SPECIAL NAMESThe International System of Units assigns special names to 22 derived units, which includes two dimensionless derived units, the radian (rad) and the steradian (sr) [...More...]  "SI Derived Unit" on: Wikipedia Yahoo 

International System Of Units The INTERNATIONAL SYSTEM OF UNITS (abbreviated as SI, from the French _Système internationale (d'unités)_) is the modern form of the metric system , and is the most widely used system of measurement . It comprises a coherent system of units of measurement built on seven base units . The system also establishes a set of twenty prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units. The system was published in 1960 as a result of an initiative that began in 1948. It is based on the metre–kilogram–second system of units (MKS) rather than any variant of the centimetre–gram–second system (CGS). SI is intended to be an evolving system, so prefixes and units are created and unit definitions are modified through international agreement as the technology of measurement progresses and the precision of measurements improves. The 24th and 25th General Conferences on Weights and Measures (CGPM) in 2011 and 2014, for example, discussed a proposal to change the definition of the kilogram , linking it to an invariant of nature rather than to the mass of a material artefact, thereby ensuring longterm stability. The motivation for the development of the SI was the diversity of units that had sprung up within the CGS systems and the lack of coordination between the various disciplines that used them [...More...]  "International System Of Units" on: Wikipedia Yahoo 

SI Base Unit The International System of Units International System of Units (SI) defines seven units of measure as a basic set from which all other SI units can be derived . The SI BASE UNITS and their physical quantities are the metre for measurement of length , the kilogram for mass , the second for time , the ampere for electric current , the kelvin for temperature , the candela for luminous intensity , and the mole for amount of substance . The SI base units form a set of mutually independent dimensions as required by dimensional analysis commonly employed in science and technology. The names and symbols of SI base units are written in lowercase, except the symbols of those named after a person, which are written with an initial capital letter. For example, the metre (US English: meter) has the symbol m, but the kelvin has symbol K, because it is named after Lord Kelvin Kelvin and the ampere with symbol A is named after AndréMarie Ampère AndréMarie Ampère . Other units, such as the litre (US English: liter), are formally not part of the SI, but are accepted for use with SI [...More...]  "SI Base Unit" on: Wikipedia Yahoo 

Units Of Measurement A UNIT OF MEASUREMENT is a definite magnitude of a quantity , defined and adopted by convention or by law, that is used as a standard for measurement of the same quantity. Any other value of that quantity can be expressed as a simple multiple of the unit of measurement. For example, length is a physical quantity . The metre is a unit of length that represents a definite predetermined length. When we say 10 metres (or 10 m), we actually mean 10 times the definite predetermined length called "metre". The definition, agreement, and practical use of units of measurement have played a crucial role in human endeavour from early ages up to this day. Different systems of units used to be very common. Now there is a global standard, the International System of Units International System of Units (SI), the modern form of the metric system . In trade, WEIGHTS AND MEASURES is often a subject of governmental regulation, to ensure fairness and transparency. The International Bureau of Weights and Measures (BIPM) is tasked with ensuring worldwide uniformity of measurements and their traceability to the International System of Units International System of Units (SI). Metrology is the science for developing nationally and internationally accepted units of weights and measures [...More...]  "Units Of Measurement" on: Wikipedia Yahoo 

Dimensionless Quantity In dimensional analysis , a DIMENSIONLESS QUANTITY is a quantity to which no physical dimension is applicable. It is also known as a BARE NUMBER or a QUANTITY OF DIMENSION ONE. Dimensionless quantities are widely used in many fields, such as mathematics , physics , engineering , and economics . By contrast, examples of quantities with dimensions are length , time , and speed , which are measured in dimensional units, such as metre , second and metre per second . CONTENTS * 1 History * 2 Pure numbers * 3 Ratios, proportions, and angles * 4 Buckingham π theorem * 4.1 Example * 5 Dimensionless physical constants * 6 Other quantities produced by nondimensionalization * 6.1 Physics Physics and engineering * 6.2 Chemistry * 6.3 Other fields * 7 See also * 8 References HISTORY See also: Dimensional analysis § History Quantities having dimension 1, habitually called _dimensionless quantities_, regularly occur in sciences, and are formally treated within the field of dimensional analysis . In the nineteenth century, French mathematician Joseph Fourier and Scottish physicist James Clerk Maxwell led significant developments in the modern concepts of dimension and unit . Later work by British physicists Osborne Reynolds and Lord Rayleigh contributed to the understanding of dimensionless numbers in physics [...More...]  "Dimensionless Quantity" on: Wikipedia Yahoo 

Power (mathematics) EXPONENTIATION is a mathematical operation , written as BN, involving two numbers, the BASE b and the EXPONENT n. When n is a positive integer , exponentiation corresponds to repeated multiplication of the base: that is, bn is the product of multiplying n bases: b n = b b n {displaystyle b^{n}=underbrace {btimes cdots times b} _{n}} The exponent is usually shown as a superscript to the right of the base. In that case, bn is called b raised to the nth power, b raised to the power of n, or the nth power of b. When n is a positive integer and b is not zero, b−n is naturally defined as 1/bn, preserving the property bn × bm = bn + m. With exponent −1, b−1 is equal to 1/b, and is the reciprocal of b. The definition of exponentiation can be extended to allow any real or complex exponent. Exponentiation by integer exponents can also be defined for a wide variety of algebraic structures, including matrices . Exponentiation is used extensively in many fields, including economics , biology , chemistry , physics , and computer science , with applications such as compound interest , population growth , chemical reaction kinetics , wave behavior, and publickey cryptography [...More...]  "Power (mathematics)" on: Wikipedia Yahoo 

Square Metre The SQUARE METRE (International spelling as used by the International Bureau of Weights and Measures ) or SQUARE METER (American spelling ) is the SI derived unit of area , with symbol m2 (33A1 in Unicode ). It is defined as the area of a square whose sides measure exactly one metre . The square metre is derived from the SI base unit of the metre, which itself is defined as the length of the path travelled by light in absolute vacuum during a time interval of 1/299,792,458 of a second . Adding and subtracting SI prefixes creates multiples and submultiples; however, as the unit is squared, the order of magnitude difference between units doubles from their comparable linear units. For example, a kilometre is 1000 times the length of a metre, but a square kilometre is 1,000,000 times the area of a square metre. CONTENTS * 1 SI prefixes applied * 2 Conversions * 3 See also * 4 Notes * 5 External links SI PREFIXES APPLIEDThe square metre may be used with all SI prefixes used with the metre [...More...]  "Square Metre" on: Wikipedia Yahoo 

Density The DENSITY, or more precisely, the VOLUMETRIC MASS DENSITY, of a substance is its mass per unit volume . The symbol most often used for density is _ρ_ (the lower case Greek letter rho ), although the Latin letter _D_ can also be used. Mathematically, density is defined as mass divided by volume: = m V , {displaystyle rho ={frac {m}{V}},} where _ρ_ is the density, _m_ is the mass, and _V_ is the volume. In some cases (for instance, in the United States oil and gas industry), density is loosely defined as its weight per unit volume , although this is scientifically inaccurate – this quantity is more specifically called specific weight . For a pure substance the density has the same numerical value as its mass concentration . Different materials usually have different densities, and density may be relevant to buoyancy , purity and packaging . Osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser. To simplify comparisons of density across different systems of units, it is sometimes replaced by the dimensionless quantity "relative density " or "specific gravity ", i.e. the ratio of the density of the material to that of a standard material, usually water. Thus a relative density less than one means that the substance floats in water. The density of a material varies with temperature and pressure [...More...]  "Density" on: Wikipedia Yahoo 

Kilogram Per Cubic Metre KILOGRAM PER CUBIC METRE is an SI derived unit of density , defined by mass in kilograms divided by volume in cubic metres . The official SI symbolic abbreviation is kg·m−3, or equivalently either kg/m3 or kg m 3 {displaystyle {tfrac {text{kg}}{{text{m}}^{3}}}!} . CONTENTS * 1 Conversions * 2 Relation to other measures * 3 See also * 4 References * 5 External links CONVERSIONS1 kg/m3 is equivalent to: = 0.001 g/cm3 (exactly) ≈ 0.06243 lb/ft3 (approximately) ≈ 0.1335 oz/gal (approximately) 1 g/cm3 = 1000 kg/m3 = 1,000,000 g/m3 (exactly) 1 lb/ft3 ≈ 16.02 kg/m3 (approximately) 1 oz/gal ≈ 7.489 kg/m3 (approximately) RELATION TO OTHER MEASURESThe kilogram was originally based on the mass of one litre of water, thus the density of water is about 1000 kg/m3 or 1 g/cm3. In chemistry , g/cm3 is more commonly used [...More...]  "Kilogram Per Cubic Metre" on: Wikipedia Yahoo 

Hertz The HERTZ (symbol: Hz) is the derived unit of frequency in the International System of Units International System of Units (SI) and is defined as one cycle per second . It is named for Heinrich Rudolf Hertz Hertz , the first person to provide conclusive proof of the existence of electromagnetic waves . Hertz Hertz are commonly expressed in multiples : kilohertz (103 Hz, kHz), megahertz (106 Hz, MHz), gigahertz (109 Hz, GHz), and terahertz (1012 Hz, THz). Some of the unit's most common uses are in the description of sine waves and musical tones , particularly those used in radio  and audiorelated applications. It is also used to describe the speeds at which computers and other electronics are driven. CONTENTS * 1 Definition * 2 History * 3 Applications * 3.1 Vibration * 3.2 Electromagnetic radiation * 3.3 Computers * 4 SI multiples * 5 See also * 6 Notes and references * 7 External links DEFINITIONThe hertz is equivalent to cycles per second , i.e., "1/second" or s 1 {displaystyle {text{s}}^{1}} [...More...]  "Hertz" on: Wikipedia Yahoo 

Metre The METRE (international spelling ) or METER (American spelling ) (from the Greek noun μέτρον, "measure") is the base unit of length in the International System of Units (SI). The SI unit symbol is M. The metre is defined as the length of the path travelled by light in a vacuum in 1/299 792 458 seconds . The metre was originally defined in 1793 as one tenmillionth of the distance from the equator to the North Pole North Pole . In 1799, it was redefined in terms of a prototype metre bar (the actual bar used was changed in 1889). In 1960, the metre was redefined in terms of a certain number of wavelengths of a certain emission line of krypton86 . In 1983, the current definition was adopted. The imperial inch is defined as 0.0254 metres (2.54 centimetres or 25.4 millimetres). One metre is about 3 3⁄8 inches longer than a yard , i.e. about 39 3⁄8 inches [...More...]  "Metre" on: Wikipedia Yahoo 

Radian The RADIAN is the standard unit of angular measure, used in many areas of mathematics . The length of an arc of a unit circle is numerically equal to the measurement in radians of the angle that it subtends; one radian is just under 57.3 degrees (expansion at A072097 ). The unit was formerly an SI supplementary unit , but this category was abolished in 1995 and the radian is now considered an SI derived unit . Separately, the SI unit of solid angle measurement is the steradian . The radian is represented by the symbol RAD. An alternative symbol is c, the superscript letter c, for "circular measure", or the letter r, but both of those symbols are infrequently used as it can be easily mistaken for a degree symbol (°) or a radius (r). So for example, a value of 1.2 radians could be written as 1.2 rad, 1.2 r, 1.2rad, or 1.2c. CONTENTS * 1 Definition * 2 History * 3 Conversions * 3.1 Conversion between radians and degrees * 3.1.1 Radian to degree conversion derivation * 3.2 Conversion between radians and gradians * 4 Advantages of measuring in radians * 5 Dimensional analysis * 6 Use in physics * 7 SI multiples * 8 See also * 9 Notes and references * 10 External links DEFINITION Radian describes the plane angle subtended by a circular arc as the length of the arc divided by the radius of the arc [...More...]  "Radian" on: Wikipedia Yahoo 

Steradian The STERADIAN (symbol: sr) or SQUARE RADIAN is the SI unit of solid angle . It is used in threedimensional geometry, and is analogous to the radian which quantifies planar angles . The name is derived from the Greek stereos for "solid" and the Latin radius for "ray, beam". The steradian, like the radian, is a dimensionless unit, essentially because a solid angle is the ratio between the area subtended and the square of its distance from the vertex: both the numerator and denominator of this ratio have dimension length squared (i.e. L2/L2 = 1, dimensionless). It is useful, however, to distinguish between dimensionless quantities of a different nature, so the symbol "sr" is used to indicate a solid angle. For example, radiant intensity can be measured in watts per steradian (W·sr−1). The steradian was formerly an SI supplementary unit , but this category was abolished in 1995 and the steradian is now considered an SI derived unit . CONTENTS * 1 Definition * 2 Other properties * 3 Analogy to radians * 4 SI multiples * 5 See also * 6 Notes * 7 References DEFINITION Section of cone (1) and spherical cap (2) that subtend a solid angle of one steradian inside a sphere A steradian can be defined as the solid angle subtended at the center of a unit sphere by a unit area on its surface. For a general sphere of radius r, any portion of its surface with area A = r2 subtends one steradian [...More...]  "Steradian" on: Wikipedia Yahoo 

Si The INTERNATIONAL SYSTEM OF UNITS (abbreviated as SI, from the French Système internationale (d'unités)) is the modern form of the metric system , and is the most widely used system of measurement . It comprises a coherent system of units of measurement built on seven base units . The system also establishes a set of twenty prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units. The system was published in 1960 as a result of an initiative that began in 1948. It is based on the metrekilogramsecond system of units (MKS) rather than any variant of the centimetre–gram–second system (CGS). SI is intended to be an evolving system, so prefixes and units are created and unit definitions are modified through international agreement as the technology of measurement progresses and the precision of measurements improves. The 24th and 25th General Conferences on Weights and Measures (CGPM) in 2011 and 2014, for example, discussed a proposal to change the definition of the kilogram , linking it to an invariant of nature rather than to the mass of a material artefact, thereby ensuring longterm stability. The motivation for the development of the SI was the diversity of units that had sprung up within the CGS systems and the lack of coordination between the various disciplines that used them [...More...]  "Si" on: Wikipedia Yahoo 

Symbol A SYMBOL is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different concepts and experiences. All communication (and data processing) is achieved through the use of symbols. Symbols take the form of words, sounds, gestures, ideas or visual images and are used to convey other ideas and beliefs. For example, a red octagon may be a symbol for "STOP". On a map, a blue line might represent a river. Numerals are symbols for numbers . Alphabetic letters may be symbols for sounds. Personal names are symbols representing individuals. A red rose may symbolize love and compassion. The variable 'x', in a mathematical equation, may symbolize the position of a particle in space. In cartography , an organized collection of symbols forms a legend for a map CONTENTS * 1 Etymology * 2 Definitions * 3 Symbols and semiotics * 4 Psychoanalysis, rhetoric and archetypes * 5 Paul Tillich * 6 Role of context in symbolism * 6.1 Historical meaning * 6.2 Context * 7 Symbolic action * 8 See also * 9 Notes * 10 External links ETYMOLOGYThe word derives from the Greek _symbolon_ (σύμβολον) meaning token or watchword [...More...]  "Symbol" on: Wikipedia Yahoo 

Physical Quantity A PHYSICAL QUANTITY is a physical property of a phenomenon , body, or substance, that can be quantified by measurement . A physical quantity can be expressed as the combination of a magnitude expressed by a number – usually a real number – and a unit ; for example, 6973167492749999999♠1.6749275×10−27 kg (the mass of the neutron ), or 7008299792458000000♠299792458 metres per second (the speed of light ). Physical quantities are measured as n u {textstyle nu} _ where n {textstyle n} is the magnitude and u {textstyle u} is the unit. For example: A boy has measured the length of a room as 3 m. Here 3 is magnitude and m (metre) is the unit. 3 m can also be written as 300 cm. The same physical quantity x {textstyle x} can be represented equivalently in many unit systems, i.e._ x = n 1 u 1 = n 2 u 2 {textstyle x=n_{1}u_{1}=n_{2}u_{2}} . CONTENTS * 1 Symbols, nomenclature * 2 Units and dimensions * 3 Base quantities * 4 General derived quantities * 4.1 Space * 4.2 Densities, flows, gradients, and moments * 5 See also * 6 References * 6.1 Computer implementations * 7 Sources SYMBOLS, NOMENCLATURE_GENERAL_: Symbols for quantities should be chosen according to the international recommendations from ISO/IEC 80000 , the IUPAP red book and the IUPAC green book [...More...]  "Physical Quantity" on: Wikipedia Yahoo 