NationMaster - Encyclopedia: Fundamental unit

A set of fundamental units is a set of units for physical quantities from which every other unit can be generated. 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. ... A physical quantity is either a quantity within physics that can be measured (e. ...

In the language of measurement, quantities are quantifiable aspects of the world, such as time, distance, velocity, mass, momentum, energy, and weight, and units are used to describe their measure. Quantities are sometimes also referred to as dimensions (i.e. "The dimensions of the package to be mailed are 12" x 8" x 4".") although the term is normally meant to apply to the class of physical quantity (length, time, mass, momentum, energy, etc.) being measured (see dimensional analysis). Various meters Measurement is the estimation or determination of extent, dimension or capacity, usually in relation to some standard or unit of measurement. ... Quantifiability is the degree to which a thing can be quantified, such as via measaurement or precise description in mathematics and science. ... A pocket watch, a device used to keep time There are two distinct views on the meaning of time. ... Distance is a numerical description of how far apart things lie. ... The velocity of an object is its total speed in a particular direction. ... Unsolved problems in physics: What causes anything to have mass? Mass is a property of a physical object that quantifies the amount of matter and energy it is equivalent to. ... In classical mechanics, momentum (pl. ... In the physical sciences, weight is a measurement of the gravitational force acting on an object. ... 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. ...

A system of fundamental quantities (or sometimes fundamental dimensions) is such that every other physical quantity (or dimension of physical quantity) can be generated from them. The traditional fundamental dimensions of physical quantity are mass, length, time, and temperature, but in principle, other fundamental quantities could be used. Some physicists have not recognized temperature as a fundamental dimension of physical quantity since it simply expresses the energy per particle per degree of freedom which can be expressed in terms of energy (or mass, length, and time). In addition, some physicists recognize electric charge as a separate fundamental dimension of physical quantity, even if it has been expressed in terms of mass, length, and time in unit systems such as the electrostatic cgs system. There are also physicists who have cast doubt on the very existence of incompatible fundamental quantities^[1]. Unsolved problems in physics: What causes anything to have mass? Mass is a property of a physical object that quantifies the amount of matter and energy it is equivalent to. ... Length is the long dimension of any object. ... A pocket watch, a device used to keep time There are two distinct views on the meaning of time. ... Fig. ... Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ... This article or section is in need of attention from an expert on the subject. ...

The fundamental units of the SI system are kilogram, second, ampere, kelvin, and mole. The metre and candela were formerly fundamental units but have been redefined in terms of the other units. They are still considered SI base units, however, mainly for historical reasons. Other units such as the newton, joule, and volt can be derived from the SI base units and are therefore termed SI derived units. Cover of brochure The International System of Units. ... The U.S. National Prototype Kilogram, which currently serves as the primary standard for measuring mass in the U.S. It was assigned to the United States in 1889 and is periodically recertified and traceable to the primary international standard, The Kilogram, held at the Bureau International des Poids et... This article is about the unit of time. ... Current can be measured by a galvanometer, via the deflection of a magnetic needle in the magnetic field created by the current. ... The Kelvin scale is a thermodynamic (absolute) temperature scale where absolute zeroâ€”the lowest possible temperature where nothing could be colder and no heat energy remains in a substanceâ€”is defined as zero kelvin (0 K). ... The mole (symbol: mol) is the SI base unit that measures an amount of substance. ... The metre, or meter (U.S.), is a measure of length. ... The candela (symbol: cd) is the SI base unit of luminous intensity (that is, power emitted by a light source in a particular direction, with wavelengths weighted by the luminosity function, a standardized model of the sensitivity of the human eye). ... The SI system of units defines seven SI base units: physical units defined by an operational definition. ... The newton (symbol: N) is the SI unit of force. ... A joule is the work done or energy required to exert a force of one newton for a distance of one metre, so the same quantity may be referred to as a newton metre or newton-metre with the symbol NÂ·m. ... Josephson junction array chip developed by NIST as a standard volt. ... SI derived units are part of the SI system of measurement units and are derived from the seven SI base units. ...

The dimension speed, for example, is length divided by time, so its unit m/s can be generated from the fundamental unit of seconds (the metre being also defined in terms of the second). Speed is the rate of motion, or equivalently the rate of change of position, many times expressed as distance d moved per unit of time t. ...

An important basic fact of dimensional analysis is that the fundamental units can be regarded as the basis of a special kind of vector space, the space of all units. This is a vector space over the field of rational numbers where the vector addition is given by the multiplication of units and the scalar multiplication is exponentiation of 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. ... In linear algebra, a basis is a minimum set of vectors that, when combined, can address every vector in a given space. ... In mathematics, a vector space (or linear space) is a collection of objects (called vectors) that, informally speaking, may be scaled and added. ... In mathematics, a rational number (commonly called a fraction) is a ratio or quotient of two integers, usually written as the vulgar fraction a/b, where b is not zero. ...

Not all physically salient values have units: dimensionless numbers occur in many fields of science. In fact, dimensionless quantities are fundamentally what we measure, even when we are measuring dimensionful quantities. We always measure a physical quantity against a like dimensioned standard. When one measures a length with a ruler or tape-measure, that person is actually counting tick marks on the ruler (a standard used to measure length) and the net result is a dimensionless number. But when that quantity is expressed as the dimensionless number attached to (multiplying) a dimensionful unit, it becomes, conceptually, a dimensionful quantity. In dimensional analysis, a dimensionless number (or more precisely, a number with the dimensions of 1) is a pure number without any physical units. ...

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