Quantitative information on the physical conditions and property, or basic relationships to coordinate activities, and efficient communication, and understanding the nature of things in science and engineering in many aspects of everyday life. Time, distance, mass and temperature, power, strength, and all other physical quantities (or parameters or variables), as well as material properties, materials and devices, and must be measured in terms of which Have the same meaning for everybody. Instrument or instrument is calibrated (that is, the functional relationship between the signal and the magnitude of the measured quantity specified) through direct or indirect comparison with embodies the standard, or generate power. Fixed or repetition of physical quantity which is taken as a unit or some or part of the unit. Thus he can any quantity measured in number (size) and the name of the module, for example, a length of 1.54 meters. The General area is called scientific activity on standards unit and measurement accuracy measurement. See units of measure
The metric system
Has been defined the basic unit of length in the metric system the decimal as one of ten million polar Earth quarter (as determined from surveys latitudes), described by m. You define the basic unit of mass in the name of Desi block cubic meters of water, to be called per kilogram.
The United States has adopted the metric conversion Act, declaring that "the United States policy should be to coordinate and plan the increasing use of the metric system in the United States," the Council established United States metric "to coordinate voluntary conversion to the metric system. However, the English units became almost universal in some industries around the world such as, oil exploration equipment dimensions, measure the height in flight. Thus it is likely that there will always be exceptions to standardization, which require special knowledge of special units for some people at least until the whole world "go metric" principle.
International system of units (SI)
And at present is creating the international system of units (abbreviated SI from the French international system unit SD) of seven independent quantities base units (table 1). And derived units for all other quantities of these seven units. In table 2 the derived SI unit are 22 with special names. These units are derived from the basic units in a coherent manner, which means their expression products and quotients of seven base units without numerical factors. All other units are derived SI similarly obtained consistently from the base SI units, a special name. For use with the SI units, there is a group of 20 prefixes (table 3) to form multiples and submultiples of the units. For the block, and will be applied to the prefixes grams instead of SI unit, kg. See dimensional analysis.
1.
SI base unit
Quantity symbol unit name *
Length of M2
Kg mass kg
2 s
Amp power supply and
Thermal temperature Kelvin K
Amount of substance Mole mol
Lighting intensity candela CD
* Quantity here and in table 2 means a measurable attribute.
SI units along with SI prefixes provide a logical and coherent framework to measure in science and industry and commerce.
In some cases, usually amounts are expressed in terms of fundamental constants of nature, and use these constants or "natural units" are unacceptable. See Basic constants
2.
SI derived units with special names
Expression
In terms of expression in terms of
Basic SI units units quantity symbol unit name
Plane angle radians rad m · M 1 = 1
Solid angle steradian SR M2 · M² = 1
Frequency Hertz Hz S-1
Newton force N m · Kg · S-2
Stress and tension Pascal Pascal N/M2 m-1 · Kg · S-2
Energy, work, quantity of heat Joule J N · M · M2 kg · S-2
Power, radiant flux Watt W J/s M2 · Kg · S-3
Quantity of electricity,
Electric charge Coulomb C و· SS · Over there
Voltage,
Electromotive force and voltage v V W/M2 A · Kg · S 3 · A-1
Capacitance farad F C V/m 2 · Kg-1 · S4 · A2
Electrical resistance ohm and OHgr. V/a M2 · Kg · S 3 · A-2
Electric S A Siemens behavior/V m 2 · Kg-1 · S3 · A2
Weber's magnetic flux WB v · S · M2 kg · S-2 · A-1
Magnetic flux density Tesla t WB/M2 kg · S-2 · A-1
Induce Henry H WB/M2 · Kg · S-2 · A-2
Celsius ° c temperature ° K
The luminous flux lumen IM CD · Real M2 · M ·. disk 2 = CD
Illuminance Lux LM 9/M2 M2 · M-4 · CD = m 2 · CD
Another (radionuclides) becquerel Bq S-1
Absorbed dose, specific
Energy imparted, kerma gray grey J/kg M2 · S-2
Dose equivalent SV SV J/kg M2 · S-2
Catalytic activity of Casal Kat S-1 · Mall
Typical examples of natural units, with their symbols, are:
And some units that are not part of the SI that it is not practical to give them up. The units accept are listed for use with the international system in table 4. It is also necessary to realize, outside the international system, the following units are used in specialized areas: logarithmic measures such as pH, DBA (decibels) and NP (napier). See atomic mass unit, DBA, electron volts
4.
Unit in use with the international system.
Value name SI unit code
Minutes, 1 minute = 60 seconds
H hour 1 hour = 60 minutes = 3600 s
Day 1 d = 24 hours = 86400 picture
° ° 1 ° = (plant genetic resources;/180) rad
Min ' 1 ' = (1/60) ° = (plant genetic resources;/10800) rad
"1" = (1/60) ' = (plant genetic resources;/648, 000) rad
L L 1 l = 1 DM3 = 10-3 M3
Metric t 1 t = 103 kg
Nepera NP-1 NP = 1
Belb B 1 B = (1/2) at 10 (NP)
* A replacement icon for "liter" since "l" can be easily confused with the numbers 1, L "icon" is recommended for use by the United States. Iz nber uses to express various logarithmic quantities values. Natural logarithms are used to obtain numerical values for quantities expressed in nepers. Wenber coherent with SI, but have not been applied as an SI unit. BThe uses the Bill to express various logarithmic quantities values. 10 base logarithms are used to obtain numerical values for quantities expressed in thongs.
Internationally accepted definitions of seven base units continued:
Block
Kilogram (kg) is equal to the mass of the international prototype kilogram. And platinum-iridium cylinder model is preserved at the International Bureau of weights and measures in Sevres, France.
A block is the only one of the base quantities and specific object standard is arbitrary. No fundamental property of matter involving the mass can be measured more accurately than is possible in the comparison between masses kilograms of weight, about 1 part in 108. See mass.
Length
Meter is defined in terms of time and the speed of light. " M is the length of the path traveled by light in vacuum during a time interval of 1/299 792 458 of a second "this definition determines the speed of light to be exactly 299 792 458 m/s and sets the meter in terms of quantity more accurately known, and II. See the light
The most accurate way to achieve scale is by measuring a distance interferometrically by counting each margin margin space is half the wavelength of the next one. This wavelength, λ, is obtained from the measured pace, and, using the relation λ = c/f, where c is the value of the speed of light in vacuum. To this end, several major criteria factor measurement of laser frequencies lodged into the narrow spectral regions molecular attractors of visible and near-infrared. These now serve stabilized laser standards of length. See standards overlap, wavelength
The interval
Second (s) is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between two HD levels of ground state of the atom cesium 133. In the best equipment and stability and accuracy of caesium frequency generator correspond with the uncertainty of a couple parts in 1015.
The second was defined long ago, physical lalkiasat and civil affairs, as well as 1/86, 400 of the average time required for a full rotation of the Earth on its axis relative to the Sun. A slight slowing in the rate of rotation of the Earth, where the average is now about 1 second per year (IE, 3 parts in 108) but with irregular fluctuations and unexplained, and thus not defined universal second Stationary. The time scale called coordinated universal time (UTC) recommended by the General Conference of weights and measures (CGPM) in 1975 and know in a way that differs from International Atomic time (TAI) by exact integer seconds. This difference is sometimes modified by using a split second positive or negative leap at the end of certain months to keep UTC agreement with time set by Duran Earth with better than 9/10 seconds. See atomic clock, measuring frequency and time
Temperature
And Kelvin (K), thermal, temperature unit is part 1/273.16 thermal temperature of the triple point of water. It should also use the Kelvin unit Alaqsa show interval or temperature differences, erature.
To provide a convenient and accurate enough to achieve practical and temperature gauge, thermometer is used, based on the values of temperatures of several reproducible equilibrium States (Specify fixed points), on the standard toolbar in the calibration temperature, vapor pressure-temperature relationship. Callable is provided between temperature fixed point formulas used to determine the relationship between the normative and temperature values. Extensive revision, which entered into force in 1990, called ITS-90. See temperature, temperature measurement
Electric current
And amps (A) is constant current which, if maintained in two straight parallel conductors of infinite length and negligible circular sections, placed 1 meter apart in vacuum, would produce between these conductors A force equal to 2 x 10-7 Newton per meter of length. See electrical standards unit
Luminance
And CGPM, in 1979, redefining the SI base unit of luminous intensity candela, also in a given direction, of a source that emits a single radiation frequency 540 × 1012 Hertz and radiation intensity in that direction of 1/683 Watt per Steradian. See the light, illuminated the effectiveness and efficiency of the flare, illumination, light intensity, radiation measurement
Amount of substance
The Mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12. When using a mole, you must select the elementary entities, and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.
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