[SciPy-dev] Add density of water to constants?

Ryan May rmay31@gmail....
Thu Oct 2 13:30:46 CDT 2008


Pauli Virtanen wrote:
> Thu, 02 Oct 2008 12:08:10 -0500, Ryan May wrote:
>> I was just cleaning up my own hand-rolled constants file and noticed
>> that the only one not already in scipy's own constants file was the
>> density of liquid water.  I'm not sure how much we want to accumulate
>> more of these physical constants in there, but here's a patch
>> nonetheless.
> 
> I'm not sure if the density of liquid water is actually a good constant.
> 
> First, it varies between 999.972 and 992.2 kg/m^3 already at temperatures 
> between 0 °C and 40 °C.
> 
> Second, the kilogram is not defined in terms of the density of water, but 
> in terms of a metal prototype weight that was manufactured based on a 
> single measurement of the density of water. The maximum density of water 
> turns out to be, funnily enough, not 1000 kg/m^3 but slightly less. [1,2]
> 
> .. [1] "Water". Wikipedia, http://en.wikipedia.org/wiki/H2O
> .. [2] "Kilogram. Wikipedia, http://en.wikipedia.org/wiki/Kilogram

Wow. Point taken.  I knew about the kilogram "definition", but never
thought about it's impact on defining density.  Granted, in meteorology,
999.972 and 992.2 are more or less the same. :)

Maybe I'll just have maintain a few meteorologically relevant constants
in a file myself then.

Ryan

-- 
Ryan May
Graduate Research Assistant
School of Meteorology
University of Oklahoma


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