Topic of the day Full Circle: On The Change In Kilogram’s Definition
How The Kilogram Has Come To Be Defined, Once Again, In Terms Of Universal Constants
As of May 20, the kilogram joined a bunch of other units — second, metre, ampere, kelvin, mole and candela — that will no longer be compared with physical objects as standards of reference. The change comes after nearly 130 years: in 1889 a platinum-iridium cylinder was used to define how much mass one kilogram represented. Now, a more abstract definition of the kilogram has been adopted in terms of fundamental constants, namely, the Planck’s constant h, and the metre and second which already have been defined in terms of universal constants such as the speed of light. With this redefinition, the range of universality of the measurement has been extended in an unprecedented way. Earlier, if a mass had to be verified to match with a standard kilogram, it would be placed on one of the pans of a common balance, while the prototype would have to be placed in the other pan — and mass would be measured against mass. Now, by using a Kibble balance, which balances mass against electromagnetic force, to measure the mass of an unknown piece, the very methodology of verification has been altered. The constants involved are known precisely and are universal numbers. Hence, whether the mass is measured on earth or, say, on the moon, it can be determined with precision.This is the culmination of a series of historical changes, which are also described by Richard S. Davis et al in their 2016 article in the journal Metrologia. Originally the definition of mass was in terms of what was then thought of as a universal physical constant. In 1791, 1 kg was defined as the mass of one litre of distilled water at its melting point. Thus, the density of water was the physical constant on which this definition hinged. In 1799, the kilogram came to be defined using a cylinder of platinum – the first time an artefact was used for this purpose. But it was also defined as equivalent to the mass of one litre of distilled water at atmospheric pressure and at about 4 degrees Celsius, the temperature at which water has the maximum density. This was done away with in 1889 when the community adopted the International Prototype of the Kilogram — a cylinder made of an alloy that’s 90% platinum and 10% iridium. The reference to the ‘physical constant’, i.e. mass of one litre of water, was abandoned. Now, as a culmination of this historical process, we come back full circle and find that the kilogram is defined again in terms of a fundamental physical constant — the Planck’s constant. Planck’s constant is a robust number to match. Not until the art of travelling at relativistic speeds, close to the speed of light, is mastered, will we have to redefine these abstract definitions. Until then, it looks like metrologists are on a stable berth.
MEANINGS AND WORDS
Meaning: several things, typically of the same kind, growing or fastened together.
Synonyms: bouquet, spray, posy, nosegay, corsage
Antonyms: spread out, release
Example Sentence: “a bunch of grapes”
Meaning: a level of quality or attainment.
Synonyms: quality, level, grade, degree, worth, calibre, merit
Antonyms: Abnormal, Atypical
Example Sentence: physical objects as standards of reference
Meaning: the action of mentioning or alluding to something.
Synonyms: mention of, allusion to, comment on, remark about
Example Sentence: “he made reference to the enormous power of the mass media”
Meaning: be entitled or appointed to act or speak for (someone), especially in an official capacity.
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Example Sentence: “Wade represented Great Britain”
Meaning: existing in thought or as an idea but not having a physical or concrete existence.
Synonyms: Theoretical, conceptual, notional, intellectual, metaphysical
Antonyms: actual, concrete
Example Sentence: “abstract concepts such as love or beauty”
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Synonyms: Embrace, Take on, Acquire, Affect, Espouse
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Meaning: never done or known before.
Synonyms: Unparalleled, unequalled, unmatched, unrivalled
Antonyms: Normal, common
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Meaning: a first or preliminary version of a device or vehicle from which other forms are developed.
Synonyms: Original, first example, first model, master, mould
Example Sentence: “the firm is testing a prototype of the weapon”
Meaning: change in character or composition, typically in a comparatively small but significant way.
Synonyms: change, make changes to, make different, make alterations to
Antonyms: preserve, stay the same
Example Sentence: “Eliot was persuaded to alter the passage”
Meaning: in exact terms; without vagueness.
Synonyms: Exactly, sharp, on the dot
Antonyms: Questionably, Unsure
Example Sentence: “the guidelines are precisely defined”
Meaning: the quality, condition, or fact of being exact and accurate.
Synonyms: Exactness, exactitude, accuracy, accurateness
Antonyms: Inaccuracy, Disregard, Ignorance
Example Sentence: “the deal was planned and executed with military precision”
Meaning: the highest or climactic point of something, especially as attained after a long time.
Synonyms: Climax, pinnacle, peak, high point, highest point, height
Example Sentence: “the deal marked the culmination of years of negotiation”
Meaning: (of a liquid) having been purified by undergoing heating and condensation.
Example Sentence: “the report is a distilled version of the main accounts”
Meaning: equal in value, amount, function, meaning, etc.
Synonyms: equal, identical; similar, parallel, analogous
Antonyms: different, dissimilar
Example Sentence: “one unit is equivalent to one glass of wine”
Meaning: attached or joined with a hinge / attach or join with or as if with a hinge.
Synonyms: depend, hang, rest, turn, pivot, centre
Example Sentence: “the ironing board was set into the wall and hinged at the bottom”
Meaning: having been deserted or left.
Synonyms: Deserted, forsaken, cast aside/off
Antonyms: Adopted, Chaste
Example Sentence: “an abandoned car”
Meaning: accurately described only by the theory of relativity.
Example Sentence: “the relativistic nature of human experience”
Meaning: strong and healthy; vigorous.
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Antonyms: Weak, frail
Example Sentence: “the Caplan family are a robust lot”
Meaning: (of an object or structure) not likely to give way or overturn; firmly fixed. Synonyms: Firm, solid, steady, secure, fixed, strong, fast, stout,
Antonyms: Unstable, rickety
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Meaning: becoming liquefied by heat.
Synonyms: Liquefy, thaw, unfreeze, defrost, soften
Antonyms: Appear, Arrive
Example Sentence: “the film will feature a car chase across a melting glacier”