Replica of the International Prototype Kilogram (IPK) on display at the Museum of Science and Industry (Cité des Science et de l’Industrie) in Paris, France. The actual IPK served as the international standard for the kilogram from 1889 until the beginning of this week.
(Image Sources: Wikipedia.org, By Japs 88 - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=19652787)
By Glenn A. Walsh
Reporting for SpaceWatchtower
This week, weight measure moved from
the 19th century to the 21st century. The
official international measurement of weight or mass, the kilogram
(kg), was redefined from a physical prototype to a fundamental
physical property of the Universe.
The kilogram is the measurement of mass
or weight, originally part of the Metric System now known as the
International System of Units (SI). In the United States which uses Imperial Units, 1 pound is
defined as 0.45359237 kilograms.
On World Metrology Day, Monday, 2019
May 20, scientists implemented the final conversion of a measure of
the SI from a physical artifact to a mathematical equation of a
universal constant.
From 1889 until this week, the kilogram
was defined as the mass of the International Prototype Kilogram
(IPK), a golf-ball sized object stored in a vault with six precise
replicas at the International Bureau of Weights and Measures [or in
French: Bureau International des Poids et Mesures
(BIPM)], located in Saint-Cloud, France on the outskirts of Paris.
Two additional precise replicas exist at the United States National
Institute of Standards and Technology in Gaithersburg, Maryland, just
outside of Washington DC. And,
several other countries around the world also possess precise
replicas.
As
a measurement standard for each country, these replicas have been
needed for science experiments that require very precise weight
measurements and for international trade in items restricted by
weight, including radioactive materials.
Manufactured
as a right-circular cylinder, the IPK is composed of a platinum alloy
known as "Pt 10Ir", which is 90% platinum and 10%
iridium (by mass). The addition of 10% iridium greatly improved the
hardness from the previous, all-plantinum kilogram definition artifact: the Kilogram
of the Archives (Kilogramme des Archives), produced as a prototype in
1799. In 1875, when it was determined to make a new kilogram
definition artifact, the Kilogram of the Archives was used to derive
the IPK.
The
decision to modernize the definition of the kilogram came last
November 16 in Versailles, France, as scientists unanimously approved
the change at a meeting of the General Conference on Weights and
Measures. However, this decision was many years in-the-making, as
scientists deliberated on how to solve a problem with the
International Prototype Kilogram.
As
an international standard, the International Prototype Kilogram (also
known to scientists as the “Big K” or “Le Grand K") was meant to
be unchanging, to ensure standardization throughout the international
system of the measurement of mass or weight. But, with a physical
artifact, this was not possible.
As
any human-made object is imperfect, so was the International Prototype
Kilogram. The IPK has lost 50 micrograms (about the weight of an
eyelash) since it was created in 1889. And, replicas in each country,
meant to be the standard for each country based on the IPK in Paris,
may have lost more, less, or no micrograms. Hence, the IPK could no
longer be a precise standard, nor could any of the replicas.
So,
beginning this-past Monday, the kilogram is now defined by a concept
from Quantum Mechanics: the Planck Constant, derived by German theoretical physicist Max Planck in 1900. Max Planck received the 1918 Nobel
Prize in Physics "in recognition of the services he rendered to
the advancement of Physics by his discovery of energy quanta".
The new definition of the kilogram is now determined to be the Planck constant, as defined by the ISO standard, set to 6.62607015×10−34 J⋅s exactly. Ironically, the old kilogram (International Prototype Kilogram) was used to measure the value of the Planck Constant.
The new definition of the kilogram is now determined to be the Planck constant, as defined by the ISO standard, set to 6.62607015×10−34 J⋅s exactly. Ironically, the old kilogram (International Prototype Kilogram) was used to measure the value of the Planck Constant.
So,
now the kilogram is defined by an unchanging standard “for all
times, for all people.”
The
original 1889 International Prototype Kilogram will now be displayed
in a museum, instead of being securely hidden-away in a vault.
The kilogram was not the only SI standard redefined on May 20. New definitions for electric current, temperature, and the amount of a substance also changed. As with the kilogram, all of these new definitions are also related to constants of the physical Universe.
The kilogram was not the only SI standard redefined on May 20. New definitions for electric current, temperature, and the amount of a substance also changed. As with the kilogram, all of these new definitions are also related to constants of the physical Universe.
Internet Links to Additional Information ---
Kilogram: Link >>> https://en.wikipedia.org/wiki/Kilogram
International Prototype Kilogram:
Link >>> https://en.wikipedia.org/wiki/International_prototype_kilogram
Planck Constant: Link >>> https://en.wikipedia.org/wiki/Planck_constant
International Bureau of Weights and Measures:
Link >>> https://en.wikipedia.org/wiki/International_Bureau_of_Weights_and_Measures
U.S. National Institute of Standards and Technology (previously, National Bureau of Standards):
Link 1 >>> https://www.nist.gov/
Link 2 >>> https://en.wikipedia.org/wiki/National_Institute_of_Standards_and_Technology
Related Blog Post ---
"Official Kilogram Standard Contaminated: Experiments Could be Affected.
The Kilogram Has Gained Weight." 2013 Jan. 6.
Link >>> https://spacewatchtower.blogspot.com/2013/01/official-kilogram-standard-contaminated.html
Source: Glenn A. Walsh Reporting for SpaceWatchtower, a project of Friends of the Zeiss.
Friday, 2019 May 24.
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gaw
Glenn A. Walsh, Informal Science Educator & Communicator:
< http://buhlplanetarium2.tripod.com/weblog/spacewatchtower/gaw/ >
Electronic Mail: < gawalsh@planetarium.cc >
Project Director, Friends of the Zeiss: < http://buhlplanetarium.tripod.com/fotz/ >
SpaceWatchtower Editor / Author: < http://spacewatchtower.blogspot.com/ >
Formerly Astronomical Observatory Coordinator & Planetarium Lecturer, original Buhl Planetarium & Institute of Popular Science (a.k.a. Buhl Science Center), Pittsburgh's science & technology museum from 1939 to 1991.
Formerly Trustee, Andrew Carnegie Free Library and Music Hall, Pittsburgh suburb of Carnegie, Pennsylvania.
Author of History Web Sites on the Internet --
* Buhl Planetarium, Pittsburgh:
< http://www.planetarium.
* Adler Planetarium, Chicago:
< http://adlerplanetarium.
* Astronomer, Educator, Optician John A. Brashear:
< http://johnbrashear.tripod.com >
* Andrew Carnegie & Carnegie Libraries:
< http://www.andrewcarnegie.
