[USMA:36427] SI units long?

[Stan Jakuba]

Two items seem missing from these "SI units are too long" discussions.   1. First, one must distinguish the term "unit" from "measurement." Contrary to the discussions, to express a measurement (a unit and a value) in SI is almost always shorter. To illustrate: -- 5 psi, 5 Pa - SI is shorter (compare "p.s. i." (3)  with "p.a." (2). Or lb/ft^2, or in.Hg  vs. Pa). -- 5,000 psi, 5 kPa - SI is shorter (compare "five thousand p.s.i."  with "five k.p.a." ). Notice that "thousand" is longer than "kilo." So is "thousandth" vs."milli" or "ten to the sixth" vs. "mega." -- 5,000 hp, 5 kW - SI is shorter (compare "five thousand horsepower" with "five kilowatt"). -- 1 millionth of an inch vs. 1 mikrometre. -- 1-3/4 in.vs. 35 mm  (one and three quart ....... ) - you got idea. -- 5 ft and 3 in, ...... -- 5 fluid ounces ..... (or is it avoirdupois ? :-) ! Endless examples. The opposites are rare by comparison. What makes SI measurements short is PREFIXES and the way they are symbolized. Prefixes are not units; they are the international names (and symbols) for numbers. One compares apples and oranges without this recognition. Most people in the world use units to express a measurement, not to discuss them for their own sake as we do.   2. Shortening of (already short) SI measurements for colloquial purposes has been done in all countries and languages of the world - from the very beginning, I'd guess. It seems a reflection on our "English language superiority complex" that we do not recognize this to exist. In fact, there are sometimes several slang expressions for a unit/measurement. They may differ from one region in the country to another, among teenagers vs. adults. etc. It is of no consequence to the "purity of SI" except that it confuses tourists and, mainly, people who learn metric from what others do instead of from what BIPM says.   For me, I like to participate in 5 k races (or 5 K - either is okay with me) as long as the writer makes it clear from the context that we are talking about road or xcountry event. A "klick" I like less because it is longer than "k" but I respect its right to exist. I might even like it better if I were a Korean-war veteran. Abroad, I like shopping in kilos, dekas, etc; no need to bather with the unit. But I do run into trouble communicating with US engineers who say "pound" and mean, respectively, psi (pressure) lb/hr or lb/min (flow, particularly steam), and, of course, force or mass.   I hope this will get us over the commonly but wrongly perceived handicap of SI "units." It should help us promoting SI for the brevity it enables (and for its other virtues, of course). Stan Jakuba    ----- Original Message ----- From: Bill Hooper To: U.S. Metric Association Sent: 06 Mar 31, Friday 22:59 Subject: [USMA:36418] Re: Units used in popular science books: buy Canadian On 2006 Mar 31 , at 5:03 PM, Jim Elwell wrote: Another way of saying this is that Table 3 of BIPM's SI document (Derived Units with Special Names) should be expanded with reasonable expediency, to help control the proliferation of such names. Jim's point is well taken, but most of the rest of this discussion has had to do with the possibility that shorter names may be reasonable for multisyllabic unit names like millimetre (4 syllables), kilopascal (4 syllable), kilogram (3 syllable), megawatt (3 syllables), etc. This is not the same thing as developing shorter names for units that are combinations of other units, which is what Table 3 refers to in the document Jim cites. BOTH of these ideas are open to valid discussion, but they are not the same. One proposes to allows kilometres per hour to be called klicks; the other allows kilogram-metres per second squared to be called newtons.  The one is arguing that we need shorter terms for any SI unit that has too many syllables (e.g. 3 or 4 or more) so that we would have to create special names for kilometres,  cubic centimetres, kilopascals, etc.  The other is arguing that we need special, shorter names for things like the kilogram-metre-squared per second-squared (there is one: it is the unit of energy, the joule) and the kilogram-metre per second (there is not one; this is a unit of momentum), etc. One can be for one of these ideas while being against the other. In any case, let us not confuse the discussion by mixing them together. Regards, Bill Hooper Fernandina Beach, Florida, USA ==========================    SImplification Begins With SI. ==========================