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Encyclopedia > SI derived unit

SI derived units are part of the SI system of measurement units and are derived from the seven SI base units. Cover of brochure The International System of Units. ... The word unit means any of several things: Unit of measurement, a fundamental quantity of measurement Units (computer program), a popular program that does unit conversion Units of energy, the units for energy measurements Units conversion by the Factor-label method Functional unit, a component of a computer system such... The SI system of units defines seven SI base units: physical units defined by an operational definition. ...

Dimensionless derived units GA_googleFillSlot("encyclopedia_square");

The following SI units are actually dimensionless ratios, formed by dividing two identical SI units. They are therefore considered by the BIPM to be derived. Formally, their SI unit is simply the number 1, but they are given these special names, for use whenever the lack of a unit might be confusing. The International Bureau of Weights and Measures is the English name of the Bureau international des poids et mesures (BIPM, often written in English Bureau International des Poids et Mesures), a standards organization, one of the three organizations established to maintain the International System of Units (SI) under the terms...

Dimensionless SI units
Name Symbol Quantity Definition
radian rad Angle The unit of angle is the angle subtended at the centre of a circle by an arc of the circumference equal in length to the radius of the circle. There are radians in a circle.
steradian sr Solid angle The unit of solid angle is the solid angle subtended at the centre of a sphere of radius r by a portion of the surface of the sphere having an area r2. There are steradians on a sphere.

The radian (symbol: rad, or a superscript c ( half circle)) is the SI unit of plane angle. ... This article is about angles in geometry. ... The steradian (ste from Greek stereos, solid) is the SI derived unit of solid angle, and the 3-dimensional equivalent of the radian. ... A solid angle is the three dimensional analog of the ordinary angle. ...

Derived units with special names

Base units can be put together to derive units of measurement for other quantities. Some have been given names.

Named units derived from SI base units
Name Symbol Quantity Expression in terms of other units Expression in terms of SI base units
hertz Hz Frequency 1/s s−1
newton N Force, Weight m∙kg/s2 m∙kg∙s−2
joule J Energy, Work, Heat N∙m m2∙kg∙s−2
watt W Power, Radiant flux J/s m2∙kg∙s−3
pascal Pa Pressure, Stress N/m2 m−1∙kg∙s−2
lumen lm Luminous flux cd∙sr = 1/cd cd
lux lx Illuminance lm/m2 = 1/(m2∙cd) m−2∙cd
coulomb C Electric charge or flux s∙A s∙A
volt V Electrical potential difference, Electromotive force W/A = J/C m2∙kg∙s−3∙A−1
ohm Ω Electric resistance, Impedance, Reactance V/A m2∙kg∙s−3∙A−2
farad F Electric capacitance C/V m−2∙kg−1∙s4∙A2
weber Wb Magnetic flux J/A m2∙kg∙s−2∙A−1
tesla T Magnetic flux density, Magnetic inductivity V∙s/m2 = Wb/m2 kg∙s−2∙A−1
henry H Inductance V∙s/A = Wb/A m2∙kg∙s−2∙A−2
siemens S Electric conductance 1/Ω m−2∙kg−1∙s3∙A2
becquerel Bq Radioactivity (decays per unit time) 1/s s−1
gray Gy Absorbed dose (of ionizing radiation) J/kg m2∙s−2
sievert Sv Equivalent dose (of ionizing radiation) J/kg m2∙s−2
katal kat Catalytic activity mol/s s−1∙mol
degree Celsius °C Thermodynamic temperature T°C = TK − 273.15
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Other quantities and units

Compound units derived from SI units
Name Symbol Quantity Expression in terms
of SI base units
square metre m2 area m2
cubic metre m3 volume m3
metre per second m·s−1 speed, velocity m·s−1
metre per second squared m·s−2 acceleration m·s−2
metre per second cubed m·s−3 jerk m·s−3
radian per second rad·s−1 angular velocity s−1
newton second N·s momentum kg·m·s−1
newton metre second N·m·s angular momentum kg·m2·s−1
newton metre N·m torque, moment of force kg·m2·s−2
reciprocal metre m−1 wavenumber m−1
kilogram per cubic metre kg·m−3 density, mass density kg·m−3
cubic metre per kilogram kg−1·m3 specific volume kg−1·m3
mole per cubic metre m−3·mol amount (-of-substance) concentration m−3·mol
cubic metre per mole m3·mol−1 molar volume m3·mol−1
joule per kelvin J·K−1 heat capacity, entropy kg·m2·s−2·K−1
joule per kelvin mole J·K−1·mol−1 molar heat capacity, molar entropy kg·m2·s−2·K−1·mol−1
joule per kilogram kelvin J·K−1·kg−1 specific heat capacity, specific entropy m2·s−2·K−1
joule per mole J·mol−1 molar energy kg·m2·s−2·mol−1
joule per kilogram J·kg−1 specific energy m2·s−2
joule per cubic metre J·m−3 energy density kg·m−1·s−2
newton per metre N·m−1 = J·m−2 surface tension kg·s−2
watt per square metre W·m−2 heat flux density, irradiance kg·s−3
watt per metre kelvin W·m−1·K−1 thermal conductivity kg·m·s−3·K−1
square metre per second m2·s−1 kinematic viscosity, diffusion coefficient m2·s−1
pascal second Pa·s = N·s·m−2 dynamic viscosity kg·m−1·s−1
coulomb per cubic metre C·m−3 electric charge density m−3·s·A
ampere per square metre A·m−2 electric current density A·m−2
siemens per metre S·m−1 conductivity kg−1·m−3·s3·A2
siemens square metre per mole S·m2·mol−1 molar conductivity kg-1·s3·mol−1·A2
farad per metre F·m−1 permittivity kg−1·m−3·s4·A2
henry per metre H·m−1 permeability kg·m·s−2·A−2
volt per metre V·m−1 electric field strength kg·m·s−3·A−1
ampere per metre A·m−1 magnetic field strength A·m−1
candela per square metre cd·m−2 luminance cd·m−2
coulomb per kilogram C·kg−1 exposure (X and gamma rays) kg−1·s·A
gray per second Gy·s−1 absorbed dose rate m2·s−3
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A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ... Area is a physical quantity expressing the size of a part of a surface. ... The cubic meter (symbol mÂ³) is the SI derived unit of volume. ... GEE GUY dimensions is called content. ... Metre per second (U.S. spelling: meter per second) is an SI derived unit of both speed (scalar) and velocity (vector), defined by distance in metres divided by time in seconds. ... Speed (symbol: v) is the rate of motion, or equivalently the rate of change of position, expressed as distance d moved per unit of time t. ... The velocity of an object is simply its speed in a particular direction. ... Metres per second squared is the SI derived unit of acceleration (scalar) and (vector), defined by distance in metres divided by time in seconds and again divided by time in seconds. ... Acceleration is the time rate of change of velocity, and at any point on a v-t graph, it is given by the slope of the tangent to that point In physics, acceleration (symbol: a) is defined as the rate of change (or derivative with respect to time) of velocity. ... Look up jerk, jolt, surge, and lurch in Wiktionary, the free dictionary. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... In classical mechanics momentum (pl. ... Gyroscope. ... In physics, torque can be thought of informally as rotational force. Torque is commonly measured in units of newton metres; although, centiNewton Meters (cNm), Foot Pounds (Lb-Ft), Inch Pounds (Lb-In) and Inch Ounces (Oz-In) are also frequently used expressions of torque. ... Wavenumber in most physical sciences is a wave property inversely related to wavelength, having units of inverse length. ... Kilogram per cubic metre is the SI measure of density and is represented as kg/m³, where kg stands for kilogram and m³ stands for cubic metre. ... Density (symbol: Ï - Greek: rho) is a measure of mass per unit of volume. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Ice melting - a classic example of entropy increasing Entropy is a concept in thermodynamics, statistical mechanics and information theory. ... The specific heat capacity (the symbol c or s, also called specific heat or SHC) of a substance is defined as heat capacity per unit mass. ... In physics, surface tension is an effect within the surface layer of a liquid that causes the layer to behave as an elastic sheet. ... In physics, thermal conductivity, k, is the intensive property of a material that indicates its ability to conduct heat. ... The pitch drop experiment at the University of Queensland. ... Schematic drawing of the effects of diffusion through a semipermeable membrane. ... The pascal second (symbol PaÂ·s) is the SI unit of dynamic viscosity. ... The pitch drop experiment at the University of Queensland. ... Electrical conductivity is a measure of a materials ability to conduct an electric current. ... Permittivity is a physical quantity that describes how an electric field affects and is affected by a dielectric medium and is determined by the ability of a material to polarize in response to an applied electric field, and thereby to cancel, partially, the field inside the material. ... In electromagnetism, permeability is the degree of magnetisation of a material that responds linearly to an applied magnetic field. ... In physics, an electric field or E-field is an effect produced by an electric charge (or a time-varying magnetic field) that exerts a force on charged objects in the field. ... Current flowing through a wire produces a magnetic field (B, labeled M here) around the wire. ... Luminance (also called luminosity) is a photometric measure of the density of luminous intensity in a given direction. ...

Conversion between kelvins and degrees Celsius

It has been suggested that this article or section be merged into Degree Celsius#Conversions. (Discuss)

A change in temperature of 1°C is equal to a change in temperature of 1K. Wikipedia does not have an article with this exact name. ... The degree Celsius (symbol: Â°C) is an SI derived unit of temperature. ...

Temperature in °C = Temperature in kelvins - 273.15

Thus, one could think of the Kelvin scale as the same as the Celsius scale, with its zero point moved down to absolute zero. This perspective is historically accurate; however, it has become more convenient to fix the standard for the kelvin, and thus the Celsius scale is derived from that standard (i.e., it now depends on absolute zero and the triple point of water with a 0.01 K offset — the boiling point of water no longer has anything to do with the official definition of degrees Celsius). Absolute zero is a fundamental lower bound on the temperature of any macroscopic system. ... In physics, the triple point of a substance is the temperature and pressure at which three phases (gas, liquid, and solid) of that substance may coexist in thermodynamic equilibrium. ...

Temperature differences are often measured in degrees Celsius; however, it doesn't matter: differences in temperature are equivalent whether kelvins or degrees Celsius are used.

Therefore, a change in temperature (ΔT), when expressed in an equation, can be calculated using either kelvins or degrees celsius so long as one is consistent.

Cover of brochure The International System of Units. ... The SI system of units defines seven SI base units: physical units defined by an operational definition. ... An SI prefix is a prefix that can be applied to an SI unit to form a decimal multiple or submultiple. ... In physics, Planck units are a system of physical units of measurement. ...

References

• I. Mills, Tomislav Cvitas, Klaus Homann, Nikola Kallay, IUPAC: Quantities, Units and Symbols in Physical Chemistry, 2nd edition (June 1993), Blackwell Science Inc (p. 72)

Results from FactBites:

 Essentials of the SI: Base & derived units (468 words) Examples of such SI derived units are given in Table 2, where it should be noted that the symbol 1 for quantities of dimension 1 such as mass fraction is generally omitted. In photometry, the unit name steradian and the unit symbol sr are usually retained in expressions for derived units. For a graphical illustration of how the 22 derived units with special names and symbols given in Table 3 are related to the seven SI base units, see relationships among SI units.
 SI derived unit - Wikipedia, the free encyclopedia (327 words) SI derived units are part of the SI system of measurement units and are derived from the seven SI base units. The unit of angle is the angle subtended at the centre of a circle by an arc of the circumference equal in length to the radius of the circle. The unit of solid angle is the solid angle subtended at the centre of a sphere of radius r by a portion of the surface of the sphere having an area r
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