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Talk:International System of Units/Archives/05/2013

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Base units table

I would like to canvass opinion regarding this proposed change to the base units table in the article.

SI base units[1][2]
Unit name Unit
symbol 		Quantity Definition (Incomplete) Dimension
symbol
metre m length
  • Original (1792): 1⁄10000000 of the meridian through Paris between the North Pole and the EquatorFG
  • Current (1983): The distance travelled by light in vaccuum in 1⁄299792458 of a second
 L
kilogram [note 1] kg mass
  • Original (1792): The gram was defined as being the weight [mass] of one cubic centimetre of pure water at its freezing point.FG
  • Current (1889): The mass of the International Prototype Kilogram
 M
second s time
  • Original (Medieval): 1⁄86400 of a day
  • Current (19xx): The duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom
 T
ampere A electric current
  • Original (1893): the unvarying current which, when passed through a solution of silver nitrate in water, deposits silver at the rate of 0.001 118 00 grams per second.IEC
  • Current (XXXX): The constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 m apart in vacuum, would produce between these conductors a force equal to 2 x 10-7 newton per metre of length
 I
kelvin K thermodynamic temperature
  • Original (XXXX): tba
  • Current (XXXX): The fraction 1/273.16 of the thermodynamic temperature of the triple point of water
 Θ
mole mol amount of substance
  • Original (XXXX): tba
  • Current (XXXX): The amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12.[note 2]
 N
candela cd luminous intensity
  • Original (XXXX): tba
  • Current (XXXX): The luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.
 J
Note
  1. ^ Despite the prefix "kilo-", the kilogram is the base unit of mass. The kilogram, not the gram, is used in the definitions of derived units.
    Nonetheless, units of mass are named as if the gram were the base unit.
  2. ^ When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles

Is the inclusion of the original definition of the base units appropriate for this article, particularly since they predate the establishment of SI? I believe that intermediate definitions would be inappropriate. (Note: The above table still needs to be completed). Martinvl (talk) 10:29, 14 November 2012 (UTC)

tba = ?1archie99 (talk) 16:32, 4 May 2013 (UTC)
What does this statement mean? Martinvl (talk) 16:45, 4 May 2013 (UTC)
tba, what does it mean? to be announced does not seem to fit. 1archie99 (talk) 10:11, 7 May 2013 (UTC)
I think in most cases the original units should be retained. In most if not all cases, they were in effect when SI was adopted circa 1960. Also, several of them are more intuitive than the modern definition (the metre is a good example of this). If there are any cases where the original definition had been changed by the time SI was adopted, we might consider using including the 1960 definition.
It is not at all clear to me the nature of the changes Martinvl is proposing. Jc3s5h (talk) 12:26, 7 May 2013 (UTC)
If you compare the table on this talk page with the one in the article, you will see that all of the "tba" statements have been filled out. (User:1archie99 responsed to me nearly six months after I posed the question). Martinvl (talk) 12:55, 7 May 2013 (UTC)
In response to User:Jc3s5h - you are obviously thinking of the "krypton-86" (1960) definition of the metre. I have no problem with that. What do we need to do about other units of measure where the redefinition was a refinement of the existing definition, such as the second being redefined in terms of the time of the earth's rotation in 1900 or 100°C being redefined as the boiling point of water at standard atmospheric pressure? Martinvl (talk) 13:06, 7 May 2013 (UTC)

Looking through the article, I see that what we now call SI was adopted by the 10th CGPM in 1954 but the name SI wasn't adopted until 1960. That same CGPM adopted the definition "The second is the fraction 1/31 556 925.975 of the length of the tropical year for 1900.0." (Quoted on page 191 of McCarthy & Seidelmann 2009; see Tropical year for full citation.)

In 1954 the metre was still defined in terms of the International Prototype Metre.

The 10th CGPM also adopted the modern definition of the kelvin (then named the degree Kelvin). Jc3s5h (talk) 19:59, 7 May 2013 (UTC)

A point of clarification - SI was formally adopted in 1960. The 1954 resolution was to clarify that that new practical system of units would be MKS-based rather than CGS based and thereby gave the CIPM a firm brief against which to work. The question on hand is which intermediate definitions should we quote - those that change the actual definition or those that change the details of the definition? I am in favour of the latter. Martinvl (talk) 21:17, 7 May 2013 (UTC)
  1. ^ Barry N. Taylor & Ambler Thompson Ed. (2008). The International System of Units (SI) (PDF). Gaithersburg, MD: National Institute of Standards and Technology. p. 23. Retrieved 2008-06-18.
  2. ^ Quantities Units and Symbols in Physical Chemistry, IUPAC
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