Hi Jim, One point that looks a little odd is that the ampere will still be a base unit and the coulomb will still be a derived units even though the unit charge of an electron will be defined in terms of coulombs and using this value, the ampere will be defined in terms of coulombs AND seconds.
If we go back to Giorgi's original paper, he stated that four units were sufficient for a coherent system (at any rate one that units mechanical and electrical systems) - the units that he recommended were length (in metres), mass (in kilograms), time (in seconds) and an electrical unit (unspecified). The ampere was chosen because it was the most easily realizable (certainly on a macroscopic level). Maybe, in the "New SI", the coulomb should become the electrical unit rather than the ampere. -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: 25 April 2011 22:26 To: U.S. Metric Association Subject: [USMA:50397] Re: FAQs now on "the New SI" page Jim, There is one answer that I question, A6. I doubt that "anyone" shall be able to realize the SI base units in terms of the exactly defined numerical values of the fundamental constants; "anywhere" at *anytime*. Answer A6 does say anyone "may" determine, (granting permission to observe), but that does not mean ability to realize the values of the SI Base Units. Merely reciting the defined numerical values of the fundamental constants is far short of actual realization of base SI unit in terms of those constants. A well equipped standards laboratory and skilled personnel will still be required to sort out the base units in terms of the constants. There will still be an important role for artifacts as secondary standards, and for teaching SI units in elementary schools. The wording of A6 can be improved. Gene. Gene. ---- Original message ---- >Date: Sun, 24 Apr 2011 22:26:46 -0500 >From: "James R. Frysinger" <[email protected]> >Subject: [USMA:50393] FAQs now on "the New SI" page >To: "U.S. Metric Association" <[email protected]> > >Folks, > >Awhile back I called attention to a new page at the BIPM's website on >"the New SI". Much discussion ensued. I had the opportunity to feed >comments from the members of this USMA mail list back to the CCU and I >did so, as I reported here at that time. > >We tried unsuccessfully to get the phrase changed from "the New SI" to >"the New SI Definitions". However, we were successful in having many >other issues explicitly addressed. Those issues and the responses to >them are posted now as FAQs on that website. Please see > http://www.bipm.org/en/si/new_si/faqs.html >for what I think to be a forthright and elegant discussion of the issues >we raised here. > >A key point that must be comprehended is put forth clearly in those >FAQs. That is, there is a distinction between the value of a constant >and the numerical value of a constant. For example, the speed of light >in vacuum is constant.* The numerical value for the speed of light >depends on the units in which that value is expressed. Consider that we >can state the value of the speed of light as > 299 792 458 m/s >or as > 186 282 397 mi/s (using mi to stand for the international mile) >and the numerical values obviously are different. The reason for that is >that the unit m/s differs in magnitude from the unit mi/s. The speed of >light is unaffected by that. Since the value is constant, changing the >size of the unit changes the size of the numerical value. Or, the other >way around, changing the size of the numerical value changes the size of >the unit. > >* For the sake of this discussion I am ignoring the effects of >relativity here. We deal with units of the SI in a proper frame of >reference. > >Jim Frysinger >Chair, IEEE SCC14 >Vice Chair, IEEE/ASTM Joint Committee for Maintaining SI 10 > >-- >James R. Frysinger >632 Stony Point Mountain Road >Doyle, TN 38559-3030 > >(C) 931.212.0267 >(H) 931.657.3107 >(F) 931.657.3108 >
