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The SI system of units defines seven SI base units: physical units defined by an operational definition. The International System of Units (abbreviated SI from the French language name Système International dUnités) is the modern form of the metric system. ...
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. ...
An operational definition of a quantity is the description of a specific process, or set of validation tests, accessible to more persons than the definer (i. ...
All other physical units can be derived from these base units: these are known as SI derived units. Derivation is by dimensional analysis. Use SI prefixes to abbreviate long numbers. SI derived units are part of the SI system of measurement units and are derived from the seven SI base units. ...
Dimensional analysis is a conceptual tool often applied in physics, chemistry, and engineering to understand physical situations involving a mix of different kinds of physical quantities. ...
An SI prefix is a prefix that can be applied to an SI unit to form a decimal multiple or submultiple. ...
The following are the base units from which all others are derived. They are dimensionally independent, with the exception of the candela. The candela was formerly a fundamental unit but has been redefined in terms of the other SI base units. Despite this, it is still considered a base unit for historical reasons. The candela (symbol: cd, Latin for candle) is one of the seven SI base units. ...
In the language of measurement, quantities are quantifiable aspects of the world, such as time, distance, velocity, mass, and weight, and units measure them. ...
| SI base units edit | | Name | Symbol | Measure | Definition | | kilogram | kg | Mass | The unit of mass is equal to the mass of the international prototype kilogram (a platinum-iridium cylinder) kept at the Bureau International des Poids et Mesures (BIPM), Sèvres, Paris (1st CGPM (1889), CR 34-38). Note that the kilogram is the only base unit with a prefix; the gram is defined as a derived unit, equal to 1/1000 of a kilogram; prefixes such as mega are applied to the gram, not the kg; e.g. Gg, not Mkg. It is also the only unit still defined by a physical prototype instead of a measurable natural phenomenon (see the kilogram article for an alternate definition). | | second | s | Time | The unit of time is the duration of exactly 9 192 631 770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium-133 atom at a temperature of 0 K (13th CGPM (1967-1968) Resolution 1, CR 103). | | metre or meter | m | Length | The unit of length is equal to the length of the path travelled by light in a vacuum during the time interval of 1/299 792 458 of a second (17th CGPM (1983) Resolution 1, CR 97). | | ampere | A | Electrical current | The unit of electrical current is the constant current which, if maintained in two straight parallel conductors, of infinite length and negligible cross-section, placed 1 metre apart in a vacuum, would produce a force between these conductors equal to 2×10 −7 newtons per metre of length (9th CGPM (1948) Resolution 7, CR 70). | | kelvin | K | Thermodynamic temperature | The unit of thermodynamic temperature (or absolute temperature) is the fraction 1/273.16 (exactly) of the thermodynamic temperature at the triple point of water (13th CGPM (1967) Resolution 4, CR 104). | | mole | mol | Quantity of matter (mass/mass) | A mole is the quantity of substance that contains the same number of elementary entities (atoms, molecules, ions, electrons or particles, depending on the substance) as there are atoms in 0.012 kilograms of pure carbon-12 (14th CGPM (1971) Resolution 3, CR 78). This number (NA) is approximately equal to 6.02214199×1023. | | candela | cd | Luminous intensity | The unit of luminous intensity is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian (16th CGPM (1979) Resolution 3, CR 100). | The international prototype, made of platinum-iridium, which is kept at the BIPM under conditions specified by the 1st CGPM in 1889. ...
Mass is a property of a physical object that quantifies the amount of matter it contains. ...
General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Atomic mass 195. ...
General Name, Symbol, Number iridium, Ir, 77 Chemical series transition metals Group, Period, Block 9, 6, d Appearance silvery white Atomic mass 192. ...
The Bureau International des Poids et Mesures (International Bureau of Weights and Measures, or BIPM) is a standards organization, one of the three organizations established to maintain the SI system under the terms of the Metre Convention. ...
Road to Sèvres, Jean-Baptiste Camille Corot, 1855-1865. ...
The Eiffel Tower has become a symbol of Paris throughout the world. ...
An SI prefix is a prefix that can be applied to an SI unit to form a decimal multiple or submultiple. ...
The gram or gramme, symbol g, is a unit of mass. ...
The international prototype, made of platinum-iridium, which is kept at the BIPM under conditions specified by the 1st CGPM in 1889. ...
Look up second in Wiktionary, the free dictionary. ...
A watch Attempting to understand time has long been a prime occupation for philosophers, scientists and artists. ...
Radiation has a variety of different meanings. ...
Hyperfine structure is a small perturbation in the energy levels (or spectral) of atoms due to the proton-electron dipole moment interaction. ...
In physics, the ground state of a quantum mechanical system is its lowest-energy state. ...
General Name, Symbol, Number caesium, Cs, 55 Chemical series alkali metals Group, Period, Block 1, 6, s Appearance silvery gold Atomic mass 132. ...
The metre (Commonwealth English) or meter (American English) (symbol: m) is the SI base unit of length. ...
In general English usage, length (symbols: l, L) is but one particular instance of distance – an objects length is how long the object is – but in the physical sciences and engineering, the word length is in some contexts used synonymously with distance. Height is vertical distance; width (or breadth...
Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength. ...
For other uses, see vacuum cleaner and Vacuum (musical group). ...
The ampere (symbol: A) is the SI base unit of electric current equal to one coulomb per second. ...
In electricity, current refers to electric current, which is the flow of electric charge. ...
In science and engineering, conductors are materials that contain movable charges of electricity. ...
The newton (symbol: N) is the SI unit of force. ...
The kelvin (symbol: K) is the SI unit of temperature, and is one of the seven SI base units. ...
Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ...
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. ...
The mole and its simple conversions into different units of measurements. ...
Matter is commonly referred to as the substance of which physical objects are composed. ...
Properties An atom (Greek άτομον from ά: non and τομον: divisible) is a submicroscopic structure found in all ordinary matter. ...
In general, a molecule is the smallest particle of a pure chemical substance that still retains its composition and chemical properties. ...
// An ion is an atom or group of atoms with a net electric charge. ...
Properties The electron is a fundamental subatomic particle that carries a negative electric charge. ...
Particles erupt from the collision point of two relativistic (100GeV) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ...
General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ...
Avogadros number, also called Avogadros Constant (NA) is a large constant used in chemistry and physics. ...
The candela (symbol: cd, Latin for candle) is one of the seven SI base units. ...
Luminous intensity is a measure of the energy emitted by a light source in a particular direction. ...
Something which is monochromatic has a single color. ...
Radiation has a variety of different meanings. ...
The hertz (symbol: Hz) is the SI unit of frequency. ...
The watt (symbol: W) is the SI derived unit of power. ...
The steradian (ste from Greek stereos, solid) is the SI derived unit of solid angle, and the 3-dimensional equivalent of the radian. ...
See also
The International System of Units (abbreviated SI from the French language name Système International dUnités) is the modern form of the metric system. ...
SI derived units are part of the SI system of measurement units and are derived from the seven SI base units. ...
An SI prefix is a prefix that can be applied to an SI unit to form a decimal multiple or submultiple. ...
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