09-13-2010, 12:49 AM
Hi,
Thank you. That is indeed correct and I've deleted it from the Standard Metric Rant of which this post was version 0.0.1. The US military uses those two numbers (0 F and 100 F) as indicators for when additional manpower is needed. For every degree below 0 F, the military considers a 2% loss of efficiency. There's a similar correction for above 100 F, though I can't remember the actual ratio.
The freezing point, yes, for the difference between solid and liquid is critical. But there is no particular advantage to labeling it 0 or 32 or 273. The boiling point, no, for water does not boil naturally except in a few spots. That water boils and generates steam and can be used for cooking are all fine and good. But the *number* at which that phenomenon happens is of no practical use. For thermodynamical calculations, only an absolute scale works. And for everyday use, then pasta comes out the same at 100 C as it does at 212 F -- and no cook that I know of measures it anyway.
Actually, water is a terrible substance to use as a standard. First, its property of dissolving nearly everything (which earns it the title of the universal solvent) means that any water you start with is going to contain many impurities. It also means that whatever apparatus you use to purify it will probably partially dissolve, introducing its own impurities. Second, the relatively steep lines of its phase transitions mean that small errors in the pressure yields a larger error in the temperature than would be the case with other materials. I shared an apartment at Los Alamos with a chemist that needed precise and accurate measurements of temperature. After two months, he quit trying to use water and went to the Peltier effect and a large brass slug.
Well, first, my point is that the Kelvin and Celsius systems are compromises. Compromises exactly for the reason of convenience and nothing more. Unlike some of the other compromises (Angstrom units, for one), the relation between the two scales is additive and not based on a factor of ten. So, I'm not so much saying that they are inferior to Fahrenheit as that they are inconsistent with the concept of metrication.
And, second, the right thing to have done would have been to make the triple point of water (or some other unique point in the pressure temperature plane) a single digit and multiple of ten. Like 300. Then, at least, a scale based on absolute zero and one handy for common use would at least have a simple conversion.
--Pete
(09-12-2010, 11:54 PM)Jester Wrote: The Fahrenheit values of zero and one hundred are worth nothing. One, or five degrees above or below zero, or one hundred, and nothing special at all happens. It is not a threshold of any relevant kind, practical or theoretical. I don't even know what to make of "start[ing] to lose efficiency" - are you saying that humans operate with no loss of efficiency between these points? How do you know when you "start" to lose efficiency? And why would that be a relevant marker even for a practical temperature system?
Thank you. That is indeed correct and I've deleted it from the Standard Metric Rant of which this post was version 0.0.1. The US military uses those two numbers (0 F and 100 F) as indicators for when additional manpower is needed. For every degree below 0 F, the military considers a 2% loss of efficiency. There's a similar correction for above 100 F, though I can't remember the actual ratio.
Quote:The freezing and boiling points of water, OTOH, are of enormous practical, everyday usage.
The freezing point, yes, for the difference between solid and liquid is critical. But there is no particular advantage to labeling it 0 or 32 or 273. The boiling point, no, for water does not boil naturally except in a few spots. That water boils and generates steam and can be used for cooking are all fine and good. But the *number* at which that phenomenon happens is of no practical use. For thermodynamical calculations, only an absolute scale works. And for everyday use, then pasta comes out the same at 100 C as it does at 212 F -- and no cook that I know of measures it anyway.
Quote:Water is a very natural, practical reference point. Zero and one hundred are physical thresholds - you can tell when you've reached them (suitably adjusted for pressure) pretty much immediately by its effects on the water surrounding us.
Actually, water is a terrible substance to use as a standard. First, its property of dissolving nearly everything (which earns it the title of the universal solvent) means that any water you start with is going to contain many impurities. It also means that whatever apparatus you use to purify it will probably partially dissolve, introducing its own impurities. Second, the relatively steep lines of its phase transitions mean that small errors in the pressure yields a larger error in the temperature than would be the case with other materials. I shared an apartment at Los Alamos with a chemist that needed precise and accurate measurements of temperature. After two months, he quit trying to use water and went to the Peltier effect and a large brass slug.
Quote:Kelvin is no doubt more useful for scientific measurements, because it starts in the ultimate physically justifiable point, absolute zero. But it is damned annoying to use numbers from 250-350 to describe everyday temperatures, and if we have to use a compromise system, Celsius/Centigrade seems like a good one.
Well, first, my point is that the Kelvin and Celsius systems are compromises. Compromises exactly for the reason of convenience and nothing more. Unlike some of the other compromises (Angstrom units, for one), the relation between the two scales is additive and not based on a factor of ten. So, I'm not so much saying that they are inferior to Fahrenheit as that they are inconsistent with the concept of metrication.
And, second, the right thing to have done would have been to make the triple point of water (or some other unique point in the pressure temperature plane) a single digit and multiple of ten. Like 300. Then, at least, a scale based on absolute zero and one handy for common use would at least have a simple conversion.
--Pete
How big was the aquarium in Noah's ark?