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For instance, K20, the US's primary standard, originally had an official mass of 1 kg − 39 μg (micrograms) in 1889; that is to say, K20 was 39 μg less than the IPK. A verification performed in 1948 showed a mass of 1 kg − 19 μg. The latest verification performed in 1989 shows a mass precisely identical to its original 1889 value.
The kilogram (also spelled kilogramme [1]) is the base unit of mass in the International System of Units (SI), having the unit symbol kg. [1] The word "kilogram" is formed from the combination of the metric prefix kilo- (meaning one thousand) and gram ; [ 2 ] it is colloquially shortened to " kilo " (plural "kilos").
The base units are defined in terms of the defining constants. For example, the kilogram is defined by taking the Planck constant h to be 6.626 070 15 × 10 −34 J⋅s, giving the expression in terms of the defining constants [1]: 131 1 kg = (299 792 458) 2 / (6.626 070 15 × 10 −34)(9 192 631 770) h Δν Cs / c 2 .
In 2018, scientists redefined the kilogram related to the basic electromagnetic principles. But a new study suggests that something similar could be done with gravitational principles as well.
Although the definition of the kilogram remained unchanged throughout the 20th century, the 3rd CGPM in 1901 clarified that the kilogram was a unit of mass, not of weight. The original batch of 40 prototypes (adopted in 1889) were supplemented from time to time with further prototypes for use by new signatories to the Metre Convention. [66]
[a] Also, in practice, any of numerous official replicas of it. Current (2019): The kilogram is defined by setting the Planck constant h exactly to 6.626 070 15 × 10 −34 J⋅s (J = kg⋅m 2 ⋅s −2), given the definitions of the metre and the second. [7] Then the formula would be kg = h / 6.626 070 15 × 10 −34 ⋅m 2 ⋅s −1 ...
kilogram: kg mass "The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.626 070 15 × 10 −34 when expressed in the unit J s, which is equal to kg m 2 s −1, where the metre and the second are defined in terms of c and ∆ν Cs." [1]
2019 definition: The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.626 070 15 × 10 −34 when expressed in the unit J⋅s, which is equal to kg⋅m 2 ⋅s −1, where the metre and the second are defined in terms of c and Δν Cs.