WikiVisually
Infinite photos and videos for every Wiki article · Find something interesting to watch in seconds
Crown Jewels Best Campuses Celebrities Wars and Battles Orders and Medals Great Cities Supercars Presidents Largest Palaces Animals British Monarchs Ancient Marvels Great Museums Tallest Buildings Largest Empires History by Country Famous Castles Recovered Treasures Rare Coins Sports Wonders of Nature Countries of the World Great Artists Richest US Counties World Banknotes Kings of France
more top lists
History
2019 redefinition of the SI base units
Videos
Page
In 2019, four of the seven SI base units specified in the International System of Quantities were redefined in terms of natural physical constants, rather than human artifacts such as the standard kilogram. Effective 20 May 2019, the 144th anniversary of the Metre Convention, the kilogram, ampere, kelvin, and mole are now defined by setting exact numerical values, when expressed in SI units, for the Planck constant, the elementary electric charge, the Boltzmann constant, and the Avogadro constant, respectively. The second, metre, and candela had previously been redefined using physical constants. The four new definitions aimed to improve the SI without changing the value of any units, ensuring continuity with existing measurements. In November 2018, the 26th General Conference on Weights and Measures (CGPM) unanimously approved these changes, which the International Committee for Weights and Measures (CIPM) had proposed earlier that year after determining that previously agreed conditions for the change had been met. These conditions were satisfied by a series of experiments that measured the constants to high accuracy relative to the old SI definitions, and were the culmination of decades of research.
Mass drift over time of national prototypes K21–K40, plus two of the international prototype's sister copies: K32 and K8(41). All mass changes are rel
Mass drift over time of national prototypes K21–K40, plus two of the international prototype's sister copies: K32 and K8(41). All mass changes are relative to the IPK.
A Kibble balance, which was used to measure the Planck constant in terms of the international prototype of the kilogram.
A Kibble balance, which was used to measure the Planck constant in terms of the international prototype of the kilogram.
A near-perfect sphere of ultra-pure silicon – part of the now-defunct Avogadro project, an International Avogadro Coordination project to determine th
A near-perfect sphere of ultra-pure silicon – part of the now-defunct Avogadro project, an International Avogadro Coordination project to determine the Avogadro constant
International Prototype of the Kilogram
Videos
Page
The International Prototype of the Kilogram is an object whose mass was used to define the kilogram from 1889, when it replaced the Kilogramme des Archives, until 2019, when it was replaced by a new definition of the kilogram based entirely on physical constants. During that time, the IPK and its duplicates were used to calibrate all other kilogram mass standards on Earth.
The International Prototype Kilogram, stored in a vault in Paris, was replaced in 2019 by a formula that uses the Planck constant, since the IPK’s mas
The International Prototype Kilogram, stored in a vault in Paris, was replaced in 2019 by a formula that uses the Planck constant, since the IPK’s mass is unstable over time.
National prototype kilogram K20, one of two prototypes stored at the US National Institute of Standards and Technology in Gaithersburg, Maryland, whic
National prototype kilogram K20, one of two prototypes stored at the US National Institute of Standards and Technology in Gaithersburg, Maryland, which serve as primary standards for defining all units of mass and weight in the United States. This is a replica for public display, shown as it is normally stored, under two bell jars.
Mass drift over time of national prototypes K21–K40, plus two of the IPK's sister copies: K32 and K8(41). All mass changes are relative to the IPK. Th
Mass drift over time of national prototypes K21–K40, plus two of the IPK's sister copies: K32 and K8(41). All mass changes are relative to the IPK. The initial 1889 starting-value offsets relative to the IPK have been nulled. The above are all relative measurements; no historical mass-measurement data is available to determine which of the prototypes has been most stable relative to an invariant of nature. There is the distinct possibility that all the prototypes gained mass over 100 years and that K21, K35, K40, and the IPK simply
A replica of the prototype kilogram on display at Cité des Sciences et de l'Industrie in Paris, featuring the protective double glass bell.
A replica of the prototype kilogram on display at Cité des Sciences et de l'Industrie in Paris, featuring the protective double glass bell.