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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 

Speed Of Light The SPEED OF LIGHT in vacuum , commonly denoted _C_, is a universal physical constant important in many areas of physics . Its exact value is 7008299792458000000♠299,792,458 metres per second (approximately 7008300000000000000♠3.00×108 m/s, or 186,282 mi/s); it is exact because the unit of length, the metre , is defined from this constant and the international standard for time . According to special relativity , _c_ is the maximum speed at which all conventional matter and hence all known forms of information in the universe can travel. It is the speed at which all massless particles and changes of the associated fields (including light , a type of electromagnetic radiation , and gravitational waves ) travel in vacuum. Such particles and waves travel at _c_ regardless of the motion of the source or the inertial reference frame of the observer. In the theory of relativity , _c_ interrelates space and time , and also appears in the famous equation of mass–energy equivalence _E_ = _mc_2. The speed at which light propagates through transparent materials , such as glass or air, is less than _c_; similarly, the speed of radio waves in wire cables is slower than _c_. The ratio between _c_ and the speed _v_ at which light travels in a material is called the refractive index _n_ of the material (_n_ = _c_ / _v_) [...More...]  "Speed Of Light" on: Wikipedia Yahoo 

Ampere The AMPERE (symbol: A), often shortened to "amp", is the base unit of electric current in the International System of Units (SI). It is named after AndréMarie Ampère (1775–1836), French mathematician and physicist, considered the father of electrodynamics . SI defines the ampere in terms of other base units by measuring the electromagnetic force between electrical conductors carrying electric current. The earlier CGS measurement system had two different definitions of current, one essentially the same as the SI's and the other using electric charge as the base unit, with the unit of charge defined by measuring the force between two charged metal plates. The ampere was then defined as one coulomb of charge per second. In SI, the unit of charge, the coulomb, is defined as the charge carried by one ampere during one second. In the future, the SI definition may shift back to charge as the base unit, with the coulomb defined in terms of the elementary charge on electrons and protons (one coulomb equals the charge of roughly 7018624200000000000♠6.242×1018 protons) [...More...]  "Ampere" on: Wikipedia Yahoo 

Candela The CANDELA (/kænˈdɛlə/ or /kænˈdiːlə/ ; symbol: cd) is the SI base unit of luminous intensity ; that is, luminous power per unit solid angle emitted by a point light source in a particular direction. Luminous intensity is analogous to radiant intensity , but instead of simply adding up the contributions of every wavelength of light in the source's spectrum, the contribution of each wavelength is weighted by the standard luminosity function (a model of the sensitivity of the human eye to different wavelengths). A common candle emits light with a luminous intensity of roughly one candela. If emission in some directions is blocked by an opaque barrier, the emission would still be approximately one candela in the directions that are not obscured. The word candela means candle in Latin . CONTENTS * 1 Definition * 2 Explanation * 2.1 Examples * 3 Origin * 4 SI photometric light units * 4.1 Relationships between luminous intensity, luminous flux, and illuminance * 5 See also * 6 References DEFINITIONLike most other SI base units, the candela has an operational definition —it is defined by a description of a physical process that will produce one candela of luminous intensity [...More...]  "Candela" on: Wikipedia Yahoo 

Energy In physics , ENERGY is the property that must be transferred to an object in order to perform work on or to heat the object. It can be converted in form , but not created or destroyed . The SI unit of energy is the joule , which is the energy transferred to an object by the mechanical work of moving it a distance of 1 metre against a force of 1 newton . Common forms of energy include the kinetic energy of a moving object, the potential energy stored by an object's position in a force field (gravitational , electric or magnetic ), the elastic energy stored by stretching solid objects, the chemical energy released when a fuel burns, the radiant energy carried by light, and the thermal energy due to an object's temperature . Mass Mass and energy are closely related. Due to mass–energy equivalence , any object that has mass when stationary in a frame of reference (called rest mass ) also has an equivalent amount of energy whose form is called rest energy in that frame, and any additional energy acquired by the object above that rest energy will increase an object's mass. For example, with a sensitive enough scale , one could measure an increase in mass after heating an object. Living organisms require available energy to stay alive, such as the energy humans get from food . Humans get the energy they need from energy resources such as fossil fuels , nuclear fuel , or renewable energy [...More...]  "Energy" on: Wikipedia Yahoo 

Length In geometric measurements, LENGTH is the most extended dimension of an object. In the International System of Quantities , length is any quantity with dimension distance. In other contexts "length" is the measured dimension of an object. For example, it is possible to cut a length of a wire which is shorter than wire thickness. Length Length may be distinguished from height , which is vertical extent, and width or breadth, which are the distance from side to side, measuring across the object at right angles to the length. Length Length is a measure of one dimension, whereas area is a measure of two dimensions (length squared) and volume is a measure of three dimensions (length cubed). In most systems of measurement , the unit of length is a base unit , from which other units are derived. The metric length of one kilometre is equivalent to the imperial measurement of 0.62137 miles . CONTENTS * 1 History * 2 Units * 3 See also * 4 References HISTORY Measurement Measurement has been important ever since humans settled from nomadic lifestyles and started using building materials, occupying land and trading with neighbours. As society has become more technologically oriented, much higher accuracies of measurement are required in an increasingly diverse set of fields, from microelectronics to interplanetary ranging [...More...]  "Length" on: Wikipedia Yahoo 

Mass In physics , MASS is a property of a physical body . It is the measure of an object's resistance to acceleration (a change in its state of motion ) when a net force is applied. It also determines the strength of its mutual gravitational attraction to other bodies. The basic SI unit of mass is the kilogram (kg). Mass is not the same as weight , even though mass is often determined by measuring the object's weight using a spring scale , rather than comparing it directly with known masses . An object on the Moon would weigh less than it does on Earth because of the lower gravity, but it would still have the same mass. This is because weight is a force, while mass is the property that (along with gravity) determines the strength of this force. In Newtonian physics , mass can be generalized as the amount of matter in an object. However, at very high speeds, special relativity postulates that energy becomes a significant additional source of mass. Thus, any stationary body having mass has an equivalent amount of energy, and all forms of energy resist acceleration by a force and have gravitational attraction. In addition, "matter" is a loosely defined term in science, and thus cannot be precisely measured. There are several distinct phenomena which can be used to measure mass [...More...]  "Mass" on: Wikipedia Yahoo 

Time _TIME_ is an American weekly news magazine published in New York City . It was founded in 1923 and for decades was dominated by Henry Luce Henry Luce , who built a highly profitable stable of magazines. A European edition (_ Time Time Europe_, formerly known as _ Time Time Atlantic_) is published in London and also covers the Middle East, Africa and, since 2003, Latin America. An Asian edition (_ Time Time Asia_) is based in Hong Kong Hong Kong . The South Pacific edition, which covers Australia, New Zealand and the Pacific Islands , is based in Sydney Sydney , Australia. In December 2008, _Time_ discontinued publishing a Canadian advertiser edition. _Time_ has the world's largest circulation for a weekly news magazine, and has a readership of 26 million, 20 million of which are based in the United States. In mid2016, its circulation was 3,032,581, having fallen from 3.3 million in 2012. Richard Stengel was the managing editor from May 2006 to October 2013, when he joined the U.S. State Department . Nancy Gibbs has been the managing editor since October 2013 [...More...]  "Time" 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 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 

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 

Kilogram The KILOGRAM or KILOGRAMME ( SI unit symbol: KG) is the base unit of mass in the International System of Units (SI) (the Metric system ) and is defined as being equal to the mass of the _International Prototype of the Kilogram_ (IPK, also known as "Le Grand K" or "Big K"). The avoirdupois (or _international_) pound , used in both the imperial and US customary systems, is defined as exactly 6999453592370000000♠0.45359237 kg, making one kilogram approximately equal to 2.2046 avoirdupois pounds. Other traditional units of weight and mass around the world are also defined in terms of the kilogram, making the IPK the primary standard for virtually all units of mass on Earth [...More...]  "Kilogram" on: Wikipedia Yahoo 

Second The SECOND (symbol: S) (abbreviated S or SEC) is the base unit of time in the International System of Units International System of Units / Système International d'Unités (SI). It is qualitatively defined as the second division of the hour by sixty, the first division by sixty being the minute . The SI definition of second is "the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom". Seconds may be measured using a mechanical, electrical or an atomic clock . SI prefixes are combined with the word second to denote subdivisions of the second, e.g., the millisecond (one thousandth of a second), the microsecond (one millionth of a second), and the nanosecond (one billionth of a second). Though SI prefixes may also be used to form multiples of the second such as kilosecond (one thousand seconds), such units are rarely used in practice. The more common larger nonSI units of time are not formed by powers of ten; instead, the second is multiplied by 60 to form a minute, which is multiplied by 60 to form an hour , which is multiplied by 24 to form a day . The second is also the base unit of time in other systems of measurement : the centimetre–gram–second , metre–kilogram–second , metre–tonne–second , and foot–pound–second systems of units [...More...]  "Second" on: Wikipedia Yahoo 

Electric Current An ELECTRIC CURRENT is a flow of electric charge . In electric circuits this charge is often carried by moving electrons in a wire . It can also be carried by ions in an electrolyte , or by both ions and electrons such as in an ionised gas (plasma ). The SI unit SI unit for measuring an electric current is the ampere , which is the flow of electric charge across a surface at the rate of one coulomb per second. Electric current Electric current is measured using a device called an ammeter . Electric currents cause Joule heating Joule heating , which creates light in incandescent light bulbs . They also create magnetic fields , which are used in motors, inductors and generators. The moving charged particles in an electric current are called charge carriers . In metals , one or more electrons from each atom are loosely bound to the atom, and can move freely about within the metal. These conduction electrons are the charge carriers in metal conductors [...More...]  "Electric Current" on: Wikipedia Yahoo 

Kelvin The KELVIN SCALE is an absolute thermodynamic temperature scale using as its null point absolute zero , the temperature at which all thermal motion ceases in the classical description of thermodynamics . The KELVIN (symbol: K) is the base unit of temperature in the International System of Units (SI). The kelvin is defined as the fraction 1⁄273.16 of the thermodynamic temperature of the triple point of water (exactly 0.01 °C or 32.018 °F). In other words, it is defined such that the triple point of water is exactly 273.16 K. The Kelvin scale is named after the Belfastborn, Glasgow University engineer and physicist William Thomson, 1st Baron Kelvin (1824–1907), who wrote of the need for an "absolute thermometric scale". Unlike the degree Fahrenheit and degree Celsius , the kelvin is not referred to or typeset as a degree . The kelvin is the primary unit of temperature measurement in the physical sciences, but is often used in conjunction with the degree Celsius, which has the same magnitude. The definition implies that absolute zero (0 K) is equivalent to −273.15 °C (−459.67 °F) [...More...]  "Kelvin" on: Wikipedia Yahoo 

Temperature TEMPERATURE is an objective comparative measurement of hot or cold . Temperature is measured by a thermometer , where several scales and units exist for measuring temperature. The most common being the Celsius scale (with units denoted °C; formerly called _degrees centigrade_), the Fahrenheit scale (with units denoted °F), and, especially in science, the Kelvin scale (with units denoted K). The coldest theoretical temperature is absolute zero , at which the thermal motion of atoms and molecules reaches its minimum – classically, this would be a state of motionlessness, but quantum uncertainty dictates that the particles still possess a finite zeropoint energy . Absolute zero is denoted as 0 K on the Kelvin scale, −273.15 °C on the Celsius scale, and −459.67 °F on the Fahrenheit scale. The kinetic theory offers a valuable but limited account of the behavior of the materials of macroscopic bodies, especially of fluids . It indicates the absolute temperature as proportional to the average kinetic energy of the random microscopic motions of those of their constituent microscopic particles, such as electrons, atoms, and molecules, that move freely within the material. Temperature is important in all fields of natural science including physics , geology , chemistry , atmospheric sciences , medicine and biology as well as most aspects of daily life [...More...]  "Temperature" on: Wikipedia Yahoo 