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Kelvins?
4

Kelvins?

Kelvins?

(OP)
It was recently brought to my attention that the plural of the SI temperature unit "kelvin" is "kelvins."  I always thought that the singular and plural pronunciation were the same, i.e., 280 kelvin, not 280 kelvins.  Am I alone in being surprised by this?  Through six years of undergrad and grad school I never once heard anyone utter the word "kelvins" (although I heard plenty of people say "degrees kelvin," which I know is incorrect).

I am struggling to accept this and wonder what some of you think.

RE: Kelvins?

I would have to go with the singular Kelvin.
°F & °C are never expressed as Fahrenheits or Centigrades.



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RE: Kelvins?

It is not clear to me how the plural form could be used.  As an absolute unit, the kelvin is a measure of an energy state, and thus to my mind is not something that can be broken into descrete pieces that could be quantified.



RE: Kelvins?

(OP)
I'm glad to see that I'm not alone in being a bit disturbed by this.  Although I would love to say that you are both right, it turns out that the plural is "kelvins."

"Fahrenheits" is not used because the plural of degree is used instead, as in "1 degree Fahrenheit" and "10 degrees Fahrenheit."  Same for Celsius.  "Degree," however, is not used with kelvin (note also that the lowercase should be used when spelling out).

Several websites and dictionaries (including Encarta) give the plurar as kelvins.  See, for example:

http://www.ucar.edu/communications/styleguide/jk.shtml

which explicitly spells this out.

This is especially embarrassing to me because I recently corrected a colleague who used "kelvins" and was nearly 100% sure that the plural was simply kelvin.  After I did some research, it turns out he was right.  I hate it when that happens.

RE: Kelvins?

Star for you, Haf, for providing actual reference.

Still, it just don't sound right.

RE: Kelvins?

280 kelvin is not a plural.
It is a singular reading. (a singular point on the kelvin scale)

The term kelvin is pointing out the "Scale" being used.
I am not sure if Degree(s) should be used with the kelvin scale or not, but a singular number isn't a plural unless it is denoting a quantity, not a scale location.
To denote a quantity you would have to use "Degree(s)", but once again the plural would be on Degree and not kelvin.

I think they need to go back and revise the reference again (2/00)

First they say: Kelvin scale, then they truncate the reading to 280 kelvin or 280 K. Which doesn't use degrees, but still only locates a "single" point on the scale.

(The last time I delt with this was in Advanced Chemistry 1968, so maybe I'm wrong...but I'm not changing now)

RE: Kelvins?

From what I learned from some technical books in physical chemistry, in the SI system, degrees Kelvin are abbreviated as K rather than oK (no longer used), and are called kelvins.

There are 100 kelvins  between the temperatures at which water freezes and boils. Note that while Celsius, Fahrenheit and Rankine degrees are capitalized, kelvins are not. Would this mean that a plural is thus acceptable ?

RE: Kelvins?

This site US Metric Association indicates that the name of the scale is kelvin, but individual temperatures on that scale are called kelvins.

Good Luck
--------------
As a circle of light increases so does the circumference of darkness around it. - Albert Einstein

RE: Kelvins?

I think it depends on where you reside. Americans tend to use the plural of the SI units if the numeric value is greater than one. Europeans use the singular such as "189.3 volt." Of course a voltage measurement is also a point on a scale, but to my American ear "189.3 volts" sounds better since there is more than one volt.

RE: Kelvins?

2
The kelvin is the SI unit for thermodynamic temperature.  It is not a scale, and its plural is kelvins.

The official site for the SI is the BIPM in France.  Here are two links that show the plural as kelvins.

http://www1.bipm.org/en/si/si_brochure/appendix2/temperature.html

http://www1.bipm.org/utils/en/pdf/si-brochure.pdf

All SI units that are spelled are NOT capitalized.  If the unit is derived from a proper noun (e.g. a person's name), then the SYMBOL is capitalized (e.g. N for newton or K for kelvin).

The only SI units that are irregular (i.e. do not use an "s" for plural) are lux, hertz, and siemens.

According to NIST SP 811, available at:

http://ts.nist.gov/ts/htdocs/200/202/mpo_pubs.htm

derived units usually are singular.  For example, 3 m2 · K / W is said "3 square meter kelvin per watt.  But, a single unit like 3 kPa is 3 kilopascals, although 3 kilopascal is acceptable.  So stevenal's examples are both correct.

Regards,

Cory

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