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Standardization of measurement units
Measurements are most commonly made in the SI system, which contains seven fundamental units: kilogram, metre, candela, second, ampere, kelvin, and mole. Six of these units are artifact-free (defined without reference to a particular physical object which serves as a standard); the definition of one remaining unit, the kilogram is still embodied in an artifact which rests at the BIPM outside Paris. Eventually, it is hoped that new SI definitions will be uniformly artifact-free.
Artifact-free definitions fix measurements at an exact value related to a physical constant or other invariable phenomenon in nature, in contrast to standard artifacts which can be damaged or otherwise change slowly over time. Instead, the measurement unit can only ever change through increased accuracy in determining the value of the constant it is tied to.
The seven base units in the SI system. Arrows point from units to those that depend on them; as the accuracy of the former increases, so will the accuracy of the latter.The first proposal to tie an SI base unit to an experimental standard independent of fiat was by Charles Sanders Peirce (1839–1914),who proposed to define the metre in terms of the wavelength of a spectral line.This directly influenced the Michelson–Morley experiment; Michelson and Morley cite Peirce, and improve on his method. 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | Поиск по сайту:
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