2002-07-13 Jim,
I'm going to disagree with you for the following reasons: Will the Authorities on SI ever recognise these other expressions as "energy units" or just equivalence's to the joule? It is the coherency that you mention that allows us to recombine different units to equate to the joule, but that doesn't take away from the joule its position as the sole energy unit in SI. By your argument, I can say that length can be expressed in the unit of joules per newton, or newton seconds squared per kilogram, etc. Even though one can express length this way I don't think it could or would take away the uniqueness of the metre as the sole SI unit of length. The same is true for the joule. The hour not only is not a coherent unit with SI, it isn't even an SI unit. A unit such as the hour, that may have a special status (accepted) for use with SI, does not make it an SI unit. The resultant combination of an SI unit with a non-SI unit is still a non-SI unit. By your logic, we should accept the FFU as a part of SI because they can be combined with SI (farads per foot, grams per mile, watts per square inch, etc.). Of course, like the hour they would not be coherent and would relate with an odd conversion factor. I don't think so! John ----- Original Message ----- From: "James R. Frysinger" <[EMAIL PROTECTED]> To: "U.S. Metric Association" <[EMAIL PROTECTED]> Cc: "U.S. Metric Association" <[EMAIL PROTECTED]> Sent: Saturday, 2002-07-13 11:17 Subject: [USMA:21025] Re: Fwd: Energy unit TWH > kilopascal wrote: > > > > 2002-07-13 > > > > The terawatt-hour is not an SI unit. There is only one SI energy unit, the > > joule. The terawatt-hour is a combination of an SI unit, the watt and the > > non-SI time unit, the hour. > > > > The watt-hour is a unit accepted with limited use along with SI, but it in > > itself is not SI. > .... > > John, > > I have to disagree with you here. The joule is a specially named derived > unit provided for energy. But other derived units, without special > names, can be and are used to express quantities of energy, such as the > newton meter, the watt second, the pascal cubic meter, and so on. > > Marvelously, due to the coherence of the system, the numerical factor > that relates each item in that short list above to the joule is "1". > Since the hour is accepted for use with the SI, the watt hour can be > used to represent quantities of energy, but since the hour is not a > coherent unit within the SI, the conversion factor is > 1 W.h = 3.6 kJ > with the period on the line in W.h representing the raised dot for > multiplication. > > Jim > > -- > Metric Methods(SM) "Don't be late to metricate!" > James R. Frysinger, LCAMS http://www.metricmethods.com/ > 10 Captiva Row e-mail: [EMAIL PROTECTED] > Charleston, SC 29407 phone: 843.225.6789 > >
