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eftychia at 06:29am on 2004-11-13
eftychia at 06:29am on 2004-11-13Doh! No wonder my toes got cold while I was typing that last entry. 287 Kelvins according to the thermometer on my desk. I need new slippers. (The ones I have are all falling apart.)
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(Yes, I know why you use Kelvins. And I always have to do the mental conversion. Fortunately, subtracting 273 is easy.)
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My "official" reasons are: that it means never having to do conversions before making calculations using the gas law (PV=nRT); that it has psychological benefits because "270" sounds so much warmer than "-3" or "28"; and that it avoids errors in thinking that describe 90F as "twice as hot" as 45F.
"Unofficial" reasons -- that is, not my stock answers that I use as excuses to inflict the Kelvin scale on people -- include the fact that I just like the idea of having one temperature scale to use whether I'm doing science or talking about the weather. And since I live in a place where the weather does go below freezing, using an absolute scale means never having to check for a minus-sign. (And since I prefer mks units for science/engineering, Kelvin makes more sense than Rankine -- though if I wanted to simply be obscure and unique and a PITA, Rankine is less well known than Kelvin.) And that it amuses me to a) educate people by reminding them about science, b) watch the "Huh?" reactions from some people, and more importantly, c) watch the "Oh yeah, cute -- I remember that" smiles from folks who recognize what I'm talking about right away.
And -- this is a bigger reason than I usually admit to ...
... Since I grew up using Fahrenheit for everything and was in school during the abortive attempt to convert the US to metric, I like the metric system both for science and because it means not having to do conversions when conversing with people in countries that use it, but I don't get that constant reinforcement to get me properly accustomed to thinking in the metric system for everyday stuff. For Celsius, I can cheat by constantly looking at a thermometer with both scales on it, so that I'm just doing a table lookup all the time and really thinking of temperature in Fahrenheit. By constantly saying temperatures in Kelvins -- to myself, as well as aloud and in print -- I reinforce the mapping of "it feels like this" to "this number" more effectively than if I use a scale where opportunities to be lazy about it are abundant. Personal brain-wiring quirk and a workaround for it.
So, with time and practice and lots of conversion artithmetic, I'm slowly building up a mapping of "my fingers feel this cold and are moving slowly, it must be in the mid 280s; I'm perspiring indoors and it feels stuffy, but the same temperature is comfortable outdoors, it must be about 300; a slight breeze feels like a knife, it must be below 260" similar to the established-in-childhood and (constantly reinforced by every weather report on the radio or television and most bank signs) for the good old F scale.
If I lived in Canada, I'd be used to C by now. I don't. Once I've got the K mappings, the fact that converting K to C is a simple subtraction will make using C as natural as F is now.
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Somehow, those were about the reasons I thought.
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Additional thoughts about mks vs. British
I think of small volumes in milliliters; sightly larger volumes in ounces, cups, and pints; the next range is a toss up as to whether liters or quarts and gallons will pop into my head; and large volumes are in cubic meters.
I think of very small everyday distances in thousandths of an inch (guitar string thicknesses); merely small distances in millimeters; slightly larger distances come out in centimeters or inches randomly, and similarly in yards or meters with roughly equal likelihood, except for a middle range that's always in feet; when you get up to travel distances, it's miles, never kilometers. Sometimes it's minutes or hours [of non-rush-hour driving]. Unless it's short travel, in which case it's "blocks", but that's a whole 'nuther story. Clothing is all in inches.
Force: sometimes Newtons, usually ounces or pounds. Which sucks, because I really hate doing force calculations in pounds, so the moment I do math, I'm converting. If the force is weight, it's going to be in pounds or tons, unless you're handing me something with its mass labelled for me in kilograms, in which case I'll think of its weight in Newtons.
Yes, I know that many people use kilograms for weight. Yes, I know that it's not considered incorrect. It bugs me. I haven't gotten used to it. I think weight in metric, I think Newtons. So it's probably not surprising that when I think of mass it's always in kilograms or grams. The slug is just not used often enough for me to have gotten used to thinking of mass in the British system at all, and I twitch at using pounds for mass.
Small masses, such as for drugs, are, unsurprsingly, all in milligrams or grams. Though it confuses the Hell out of doctors when I use grams for that. "How much ibuprofen did you say you take?" "One gram." "You mean one tablet?" "No, I mean one gram." "You mean one milligram?" "No, I mean one gram." "How much is that?" "A thousand milligrams. One one-thousandth of a kilogram." "How many 200mg tablets is that?" "Five." [stops to think] "You mean you take a thousand milligrams?" "Isn't that what I said at first? That's a gram." Sheesh.
Velocity comes out in meters per second, feet per second, or miles per hour, depending more upon context than magnitude. On long stretches of Interstate without much other traffic around, I often find myself calculating the conversion of MPH on my speedometer to meters per second. And at some point I'll wind up describing automobile speed that way in an LJ entry not to be cute about units, but because it draws the mind to a different perspective on just how fast one is moving.
And then there are tools ... I used to own a car -- a 1978 Pontiac Catalina -- on which half the bolts were English and half the bolts were metric. So I needed two complete socket sets to work on one car. Gotta love America, eh?
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