From dwells@fits.cx.nrao.edu Wed Jan 29 18:07:02 1992 X-VM-VHeader: ("From:" "Sender:" "Resent-From" "To:" "Apparently-To:" "Cc:" "Subject:" "Date:" "Resent-Date:") nil X-VM-Bookmark: 36 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["2771" "Thu" "23" "January" "1992" "14:31:07" "GMT" "Don Wells" "dwells@fits.cx.nrao.edu " nil "59" "SI Units (was Re: AAS meeting, Atlanta)" "^From:" nil nil "1"]) Newsgroups: sci.astro In-Reply-To: metares@well.sf.ca.us's message of 23 Jan 92 06: 07:42 GMT Organization: National Radio Astronomy Observatory, Charlottesville, VA Distribution: sci From: dwells@fits.cx.nrao.edu (Don Wells) Subject: SI Units (was Re: AAS meeting, Atlanta) Date: Thu, 23 Jan 1992 14:31:07 GMT In article <29569@well.sf.ca.us> metares@well.sf.ca.us (Tom Van Flandern) gives a glossary of certain astronomical units and terminology. Some corrections are needed: TVF> Angstrom: A unit of length equal to 10^-10 meters = 10^-8 cm. ^^^^^^^^ ^^^ ^^ TVF> Used primarily to measure the wavelengths of photons of visible TVF> light. The IAU Style Manual (1989, "The Preparation of Astronomical Papers and Reports", prepared by G.A. Wilkins, President of Commission 5, on behalf of the Executive Committee of the International Astronomical Union) recommends use of SI (MKS) units, which in this context means the *nanometer*, 10^-9 meters. The Angstrom is listed in Table 7 ("Non-SI units and symbols whose continued use is deprecated", p.S24). TVF> Electron Volt: A unit of energy equal to 1.60 x 10^-12 ergs... ^^^^^^^^^^^^^^^^^^ 0.1602177 aJ (attoJoule) ("atto" = 10^-18) The eV is listed in Table 6 ("Non-SI units that are recognised for use in astronomy", p.S23), and "atto" is listed in Table 5 ("SI prefixes and symbols for multiples and submultiples"). TVF> Electromagnetic Spectrum: ... range of possible energies or TVF> wavelengths of photons... Visible light.. wavelengths.. 3,000 TVF> and 10,000 Angstroms.. infrared.. wavelength.. 1 micron and ^^^^^^^^^^^^^^^^^^^^ 300 and 1000 nm TVF> 1000 microns (= 1 millimeter). Microwave.. 1 mm and 10 cm. ^^^^^^^^^^^^ ^^^^^^^^^^ ^^ ^^ 1-1000 {\mu}m mm (both are legitimate SI units) TVF> Radio waves.. 10 cm and 10 meters... ultraviolet.. 100 Angstroms ^^^^^^ m TVF> and 3000 Angstroms... ^^^^^^^^^^^^^^^^^^ 10-300 nm Section 5.11 of the Manual ("SI Units", p.S20) says: "... The units of the centimetre-gram-second (CGS) system and other non-SI units, which will be unfamiliar to most young scientists, should not be used even though they may be considered to have some advantages over SI units by some astronomers. The IAU Executive Committee has recommended (see Appendix B) that astronomers should complete the change-over quickly, and so, for example, reports and papers for the IAU General Assembly in 1991 should all use SI units or other recognised units." -- Donald C. Wells Associate Scientist dwells@nrao.edu National Radio Astronomy Observatory +1-804-296-0277 520 Edgemont Road Fax= +1-804-296-0278 Charlottesville, Virginia 22903-2475 USA 78:31.1W, 38:02.2N From dwells@fits.cx.nrao.edu Wed Jan 29 18:07:34 1992 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["4892" "Fri" "24" "January" "1992" "18:08:43" "GMT" "Don Wells" "dwells@fits.cx.nrao.edu " nil "96" "Re: SI Units (was Re: AAS meeting, Atlanta)" "^From:" nil nil "1"]) Newsgroups: sci.astro In-Reply-To: dwells@fits.cx.nrao.edu's message of Thu, 23 Jan 1992 14: 31:07 GMT Organization: National Radio Astronomy Observatory, Charlottesville, VA Distribution: sci From: dwells@fits.cx.nrao.edu (Don Wells) Subject: Re: SI Units (was Re: AAS meeting, Atlanta) Date: Fri, 24 Jan 1992 18:08:43 GMT In article dwells@fits.cx.nrao.edu (Don Wells) writes: "... The IAU Style Manual (1989, "The Preparation of Astronomical Papers and Reports", prepared by G.A. Wilkins, President of Commission 5, on behalf of the Executive Committee of the International Astronomical Union) recommends use of SI (MKS) units..." I have received several Email messages in response to my posting on SI units, and after reading them (and answering some) I offer the following additional remarks: 1. Undergraduate Training vs. Graduate Training I was an undergraduate physics student in the early 60s, 30 years ago, and was taught in MKS (SI) units. Later in that decade, in graduate school, I encountered the CGS approach. I thought at that time that both systems were rational, each in its own way. I assumed that SI was destined to be the accepted standard, but that in that era one still needed to be bilingual. As a result of my posting on this subject I have received Email from recent graduate students who tell me that the situation I experienced 20-30 years ago still persists! I.e., physics undergraduates are still taught MKS and must still learn CGS in astronomy graduate school. The persistence of this anomaly over such a timespan is telling us something. 2. SI Units in the IAU Style Manual It is, of course, true that IAU standards are only recommendations, and that adherance to them is voluntary. However --- if the recommendation to use SI units is opposed by a large fraction (a majority?) of our community, why isn't that fraction represented in Commission 5 and/or the IAU Executive Committee? Is the persistence of usage of both MKS and CGS units purely a phenomenon of (North) American graduate departments, or is it present in astronomy departments elsewhere in the world? The IAU is *the* international organization of professional astronomers; in the end the practices it recommends should really represent the consensus of astronomers everywhere, or else those recommendations should be changed. 3. Importance of Standard Units Several decades of experience demonstrate that astronomers are able to operate with both systems of units, and that few problems are caused by the potential ambiguities. I myself don't particularly prefer either system over the other. What I *do* care about is that inconsistencies and ambiguities should be minimized in astronomical archives (both observational data and published text) as much as possible, in order to facilitate robust automated search and retrieval technology in the years to come. My worries about this problem are the real motivation for my posting on this subject. For example, if the TUNITn keywords of FITS tables do not use a consistent system of units we will surely find that it will be harder to write our data analysis software. In March 1979 Eric Greisen and I decides that the Basic FITS Agreement would specify that SI units should be used in FITS files, and that decision was recently endorsed by members of the IAU FITS Working Group and the NASA Technical Panel during the NASA-supported codification of the FITS agreements. These decisions were made precisely because of the worry that software will prove to be less robust than humans in interpreting ambiguous or inconsistent situations in our future archives. 4. Brief Bibliography * "A Physicist's Desk Reference" (The Second Edition of Physics Vade Mecum, H.L. Anderson, Editor in Chief, Am. Inst. Physics 1989) gives a detailed tabulation of SI and units conversions in section 1.02 ("The International System of Units", pp.5-10). It also contains a convenient summary of the real MKS-vs-CGS (Gaussian units) issues in section 1.05 (Physics Formulary), subsection C (Electricity and Magnetism), where the notations are compared for E&M case by case. It is clear that both systems are rational, and attractive, each in its own way. * Chicago Manual of Style says: "[section] 14.41 The International System of Units (..abbreviated "SI") is used generally by scientists around the world...". * Astrophysical Journal Instructions to Authors (1992 December 1, p.i) says: "... 3. The standard abbreviations (without periods) for SI units and some cgs units may be used..." * Monthly Notices RAS Notice to Authors (recent issue) says: "... 7. UNITS. Authors are strongly encouraged to use SI units." * Document NOST-100-0.3b (6-November-1991, "Implementation of the Flexible Image Transport System [FITS]", section 8.1.2, p.34, "TUNITn Keywords") says: "...Use of the units defined in the IAU Style Manual is recommended." -- Donald C. Wells Associate Scientist dwells@nrao.edu National Radio Astronomy Observatory +1-804-296-0277 520 Edgemont Road Fax= +1-804-296-0278 Charlottesville, Virginia 22903-2475 USA 78:31.1W, 38:02.2N From njzy@vax5.cit.cornell.edu Wed Jan 29 18:07:48 1992 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["2272" "" "24" "January" "92" "09:38:33" "EST" "T. Joseph Lazio, Cornell University" "njzy@vax5.cit.cornell.edu " nil "50" "Re: SI Units vs cgs units" "^From:" nil nil "1"]) Newsgroups: sci.astro Distribution: sci Organization: Cornell University From: njzy@vax5.cit.cornell.edu (T. Joseph Lazio, Cornell University) Subject: Re: SI Units vs cgs units Date: 24 Jan 92 09:38:33 EST Keywords: SI vs cgs Summary: Oh, no, not another change! In article , dwells@fits.cx.nrao.edu (Don Wells) writes: > In article <29569@well.sf.ca.us> metares@well.sf.ca.us (Tom Van > Flandern) gives a glossary of certain astronomical units and > terminology. Some corrections are in order [...] > > TVF> Electromagnetic Spectrum: ... range of possible energies or > TVF> wavelengths of photons... Visible light.. wavelengths.. 3,000 > TVF> and 10,000 Angstroms.. infrared.. wavelength.. 1 micron and > ^^^^^^^^^^^^^^^^^^^^ > 300 and 1000 nm > > TVF> 1000 microns (= 1 millimeter). Microwave.. 1 mm and 10 cm. > ^^^^^^^^^^^^ ^^^^^^^^^^ ^^ ^^ > 1-1000 {\mu}m mm (both are legitimate SI units) > > TVF> Radio waves.. 10 cm and 10 meters... ultraviolet.. 100 Angstroms > ^^^^^^ > m > > TVF> and 3000 Angstroms... > ^^^^^^^^^^^^^^^^^^ > 10-300 nm > > Section 5.11 of the Manual ("SI Units", p.S20) says: "... The units of > the centimetre-gram-second (CGS) system and other non-SI units, which > will be unfamiliar to most young scientists, should not be used even > though they may be considered to have some advantages over SI units by > some astronomers. The IAU Executive Committee has recommended (see > Appendix B) that astronomers should complete the change-over quickly, > and so, for example, reports and papers for the IAU General Assembly > in 1991 should all use SI units or other recognised units." Sigh. After spending all my undergraduate years learning SI units, I have spent my years in grad. school changing over and becoming quite comfortable with cgs units. Am I going to have to change, again? -- T. Joseph Lazio | Why relativity? and Why 514 Space Sciences | turbulence? I really believe Ithaca, NY 14853 | [God] will have an answer for the (607) 255-6420 | first [question]. lazio@astrosun.tn.cornell.edu | -- W. Heisenberg, on his death bed ICBM: | 42 deg. 20' 08" N | STOP RAPE 76 deg. 28' 48" W | From cain@geomag.gly.fsu.edu Wed Jan 29 18:07:56 1992 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["2435" "" "26" "January" "92" "15:40:35" "GMT" "Joe Cain" "cain@geomag.gly.fsu.edu " nil "45" "Re: SI Units vs cgs units" "^From:" nil nil "1"]) Newsgroups: sci.astro,sci.geo.geology,sci.space Followup-To: sci.astro Distribution: sci Organization: Florida State University Geology Dept. From: cain@geomag.gly.fsu.edu (Joe Cain) Subject: Re: SI Units vs cgs units Date: 26 Jan 92 15:40:35 GMT In article <1992Jan24.093833.10105@vax5.cit.cornell.edu> njzy@vax5.cit.cornell.edu (T. Joseph Lazio, Cornell University) writes: >In article , >dwells@fits.cx.nrao.edu (Don Wells) writes: >> In article <29569@well.sf.ca.us> metares@well.sf.ca.us (Tom Van >> Flandern) gives a glossary of certain astronomical units and >> terminology. Some corrections are in order [...] > > Sigh. After spending all my undergraduate years learning SI units, > I have spent my years in grad. school changing over and becoming > quite comfortable with cgs units. Am I going to have to change, > again? As one who indeed encountered MKS at Caltech in the 50's but worked under Sydney Chapman at the U. of Alaska for graduate school and found him a diehard cgs person, I can indeed empathize with this uneeded confusion. However, I chose for my planetary geology text this year what I thought was the latest published (Wagner's "Introduction to the Solar System," 1991) which has a prominent table in cgs only. (He also makes the mistake of equating to old English units throught the text). Thus the emergence of SI seems slow and will require continued pressure to keep stomping on the multiplicity of systems. It would help a lot to also push hard in the US to get a complete conversion >from the old English so students see it as useful and not just more learning they should forget. The actual units can be SI compatible and still understandable if they are kept fairly simple. For my course I use c = 300,000 km/sec instead of 3x10**8 m/sec simply because it is easier to understand compared with the 150,000 km AU. However, I doubt that the SI units of density (kg/m**3) will ever supplant gm/cc simply because 1, 3, 5, are simple compared to 1000, 3000, 5000, etc. For radiation also the units can be more or less SI and still useful. I have had to convert my thinking that 5577A was apple green and 6300A red to 500, 600 nM, but this is not so bad. Microns are hard to integrate into SI thinking, but you are going to have a hard time getting radio astronomers to use units they can't relate to waveguide and antenna sizes. In summary, I think you have to keep pushing SI, be kind to those whose thinking was frozen decades ago, and try to use the smallest number of units to promote the most interdisciplinary understanding. Joseph Cain cain@geomag.gly.fsu.edu cain@fsu.bitnet scri::cain From gill@physics.ubc.ca Wed Jan 29 18:07:57 1992 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["448" "Mon" "27" "January" "1992" "17:35:12" "GMT" "Arnold Gill visiting astrophys phd std" "gill@physics.ubc.ca " nil "9" "Re: SI Units vs cgs units" "^From:" nil nil "1"]) Newsgroups: sci.astro Nntp-Posting-Host: physics.ubc.ca Organization: University of British Columbia, Vancouver, B.C., Canada Distribution: sci From: gill@physics.ubc.ca (Arnold Gill visiting astrophys phd std) Subject: Re: SI Units vs cgs units Date: Mon, 27 Jan 1992 17:35:12 GMT cain@geomag.gly.fsu.edu (Joe Cain) writes: > In summary, I think you have to keep pushing SI, be kind to those >whose thinking was frozen decades ago, and try to use the smallest >number of units to promote the most interdisciplinary understanding. And everyone also has to stay `bilingual' so that one can understand papers written in the `Dark Ages'. -- Arnold Gill --- astrophysician trainee in exile gill@physics.ubc.ca From gaetz@julian.uwo.ca Wed Jan 29 18:07:59 1992 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["1510" "Mon" "27" "January" "1992" "22:35:05" "GMT" "Terry Gaetz" "gaetz@julian.uwo.ca " nil "32" "Re: SI Units vs cgs units" "^From:" nil nil "1"]) Newsgroups: sci.astro Organization: Dept. of Astronomy, Univ. of Western Ontario Distribution: sci From: gaetz@julian.uwo.ca (Terry Gaetz) Subject: Re: SI Units vs cgs units Date: Mon, 27 Jan 1992 22:35:05 GMT In article gill@physics.ubc.ca (Arnold Gill visiting astrophys phd std) writes: >cain@geomag.gly.fsu.edu (Joe Cain) writes: >> In summary, I think you have to keep pushing SI, be kind to those >>whose thinking was frozen decades ago, and try to use the smallest >>number of units to promote the most interdisciplinary understanding. > > And everyone also has to stay `bilingual' so that one can understand papers > written in the `Dark Ages'. 'Bilingualism' will stay important, too; too many standard reference tables have used (and new ones continue to use) non-SI units. It is not only North American astronomers who persist in using non-SI units, either - see many physics papers and reference tables: . "Atomic Transition Probabilities: Iron through Nickel" (1988) - wavelengths in angstroms, energies in cm^-1 (This is an NBS/NSRDS publication to boot!) . National Institute for Fusion Science (Nagoya, Japan) "Total and Partial Cross Sections of Electron Transfer Processes for Be^q+...", preprint, (Jun, 1991) - energy in eV, cross sections in cm^2 "Observation of Parallel Viscosity in the CHS Heliotron/Torsatron", preprint, (Jan, 1991) - temperature in eV, density in 10^13 cm^-3, velocity in km s^-1, viscosity in m^2 s^-1 SI may be the mandated standard, but I don't see cgs and non-SI units going away anytime soon. -- Terry Gaetz -- gaetz@julian.uwo.ca From mcdonald@aries.scs.uiuc.edu Wed Jan 29 18:08:00 1992 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["2694" "Mon" "27" "January" "1992" "14:46:48" "GMT" "Doug McDonald" "mcdonald@aries.scs.uiuc.edu " nil "61" "Re: SI Units vs cgs units" "^From:" nil nil "1"]) Newsgroups: sci.astro,sci.geo.geology,sci.space Organization: University of Illinois at Urbana From: mcdonald@aries.scs.uiuc.edu (Doug McDonald) Subject: Re: SI Units vs cgs units Date: Mon, 27 Jan 1992 14:46:48 GMT In article <1992Jan26.104035.19842@mailer.cc.fsu.edu> cain@geomag.gly.fsu.edu (Joe Cain) writes: >In article <1992Jan24.093833.10105@vax5.cit.cornell.edu> njzy@vax5.cit.cornell.edu (T. Joseph Lazio, Cornell University) writes: >>In article , >>dwells@fits.cx.nrao.edu (Don Wells) writes: [SI flame wars] [Note: Im not an astronomer, I'm a physicist and chemist] I have a very strong opinion on this, one shared my many (most?) of my colleagues, including several Nobel Prize winners: A plague on those who try to force pure SI units on everybody. Point one: The metric system was originally designed to have convenient multiples of ten for every unit - grams, kilograms, gigagrams, meters, centimeters, micrometers, seconds, milliseconds, picoseconds. Why not use that which is convenient? I can remember the basic numbers (Planck's constant, mass of proton, etc.) in both MKS and cgs units. I use whichever is easier. It is trivial to convert. Point two: In the actual world it is stupid to express everythings in say, meters and seconds. Everybody I know expresses times in either picoseconds or femtoseconds when relating to actual events, because that is the times that things actually occur in our lab, for example, a laser pulse lasts roughly 1 picosecond, always between .01 and 100 picoseconds. Consider lengths - teh wavelengths of light are often expressed in microns. Now the micron happen to be one micrometer. Why worry? People express energies in that unphysical unit the "wavenumber" which indeed is not SI or cgs or anything - its not an energy unit at all, just a reciprocal wavelength. Yet it is very convenient indeed. It is just silly to try to talk about energies of molecular events induced by light in units unreleated to the commonly used measure of light, the wavelength. Then there are pressure units used in vacuum work. You will note that pressure gauges are calibrated in Torr. Everybody uses those units in the lab. Really. Except for pressures greater than one atmosphere, where they use atmospheres or even, heaven forbid, psi. I do admit to removing psi from papers and putting in atmosphere. I think that worrying about units is silly. I'd rather worry about the science. In fact, using SI units in fields where they are not normally used, such as mine, is counterproductive. IF somebody actually tries to give a talk in SI units, they will invariably be asked to give, for example, the pressures of their beam sources in either Torr or atmospheres. That is what people think in. And to the astronomers: if you want to use SI units only please remember to NEVER use AU or parsecs!!! Doug McDonald From dmark@acsu.buffalo.edu Wed Jan 29 18:08:04 1992 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["771" "" "27" "January" "92" "22:44:15" "GMT" "David Mark" "dmark@acsu.buffalo.edu " nil "18" "Re: SI Units vs cgs units" "^From:" nil nil "1"]) Newsgroups: sci.astro,sci.geo.geology,sci.space Organization: UB Nntp-Posting-Host: autarch.acsu.buffalo.edu From: dmark@acsu.buffalo.edu (David Mark) Subject: Re: SI Units vs cgs units Date: 27 Jan 92 22:44:15 GMT >The metric system was originally designed to have convenient multiples >of ten for every unit - grams, kilograms, gigagrams, meters, centimeters, >micrometers, seconds, milliseconds, picoseconds. Why not use that which is >convenient? I can remember the basic numbers (Planck's constant, mass >of proton, etc.) in both MKS and cgs units. I use whichever is easier. >It is trivial to convert. I'll ask the naive question; I hope I'm not the only sci.geo.geology subscriber who doesn't know this! I thought I knew what the 'metric system' was, and also that SI was the abbreviation for the scholarly or 'official' term for the metric system. So, what are 'cgs' and 'MKS' and how do the differ from 'SI' and 'the metric system'? David Mark dmark@sun.acsu.buffalo.edu From nick@sunburn.waterloo.edu Wed Jan 29 18:08:05 1992 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["1841" "Tue" "28" "January" "1992" "00:56:35" "GMT" "Nick Fitzpatrick" "nick@sunburn.waterloo.edu " nil "34" "Re: SI Units vs cgs units" "^From:" nil nil "1"]) Newsgroups: sci.astro,sci.geo.geology,sci.space Organization: University of Waterloo From: nick@sunburn.waterloo.edu (Nick Fitzpatrick) Subject: Re: SI Units vs cgs units Date: Tue, 28 Jan 1992 00:56:35 GMT In article <1992Jan27.224415.9284@acsu.buffalo.edu> dmark@acsu.buffalo.edu (David Mark) writes: >>The metric system was originally designed to have convenient multiples >>of ten for every unit - grams, kilograms, gigagrams, meters, centimeters, >>micrometers, seconds, milliseconds, picoseconds. Why not use that which is >>convenient? I can remember the basic numbers (Planck's constant, mass >>of proton, etc.) in both MKS and cgs units. I use whichever is easier. >>It is trivial to convert. > >I'll ask the naive question; I hope I'm not the only sci.geo.geology >subscriber who doesn't know this! > >I thought I knew what the 'metric system' was, and also that SI was the >abbreviation for the scholarly or 'official' term for the metric system. > >So, what are 'cgs' and 'MKS' and how do the differ from 'SI' and 'the metric >system'? cgs, is a length-mass-time system, with cm, g, s as the base units, it is not widely used anymore, except perhaps in the US which I here actually even uses Imperial units on occasion (I mean can you imagine!! (Flame me!) MKS (if I remember correctly) is a length-force-time system, where metre, (that is meter for our american cousins who can't spell) kg and s are the base units Nobody uses this. I even recall hearing that it is banned in some European countries! (Mind you Imperial was banned here in Canada at one point, until someone pointed out that with freedom of speech, one could not ban Imperial) SI, or Systeme Internationale, which is what we often mistakenly call the metric system, uses a length-mass-time with metres, kilograms, and seconds as the base units (+ Celcius, and a few other special things that I forget).. Derived units include Litres for volume, Newtons for force Pascals for pressure, ares, for area, etc,etc Nicholas Fitzpatrick, Waterloo, Ontario, Canada From nick@sunburn.waterloo.edu Wed Jan 29 18:08:06 1992 Status: O X-VM-v5-Data: ([nil t nil nil nil nil nil nil nil] ["1822" "Tue" "28" "January" "1992" "03:56:26" "GMT" "Nick Fitzpatrick" "nick@sunburn.waterloo.edu " nil "37" "Re: SI Units vs cgs units" nil nil nil "1"]) Newsgroups: sci.astro,sci.geo.geology,sci.space From: nick@sunburn.waterloo.edu (Nick Fitzpatrick) Subject: Re: SI Units vs cgs units Organization: University of Waterloo Date: Tue, 28 Jan 1992 03:56:26 GMT In article <1992Jan28.005635.14025@watserv1.waterloo.edu> nick@sunburn.waterloo.edu (Nick Fitzpatrick) writes: >In article <1992Jan27.224415.9284@acsu.buffalo.edu> dmark@acsu.buffalo.edu (David Mark) writes: >>>The metric system was originally designed to have convenient multiples >>>of ten for every unit - grams, kilograms, gigagrams, meters, centimeters, >>>micrometers, seconds, milliseconds, picoseconds. Why not use that which is >>>convenient? I can remember the basic numbers (Planck's constant, mass >>>of proton, etc.) in both MKS and cgs units. I use whichever is easier. >>>It is trivial to convert. >> >>I'll ask the naive question; I hope I'm not the only sci.geo.geology >>subscriber who doesn't know this! >> >>I thought I knew what the 'metric system' was, and also that SI was the >>abbreviation for the scholarly or 'official' term for the metric system. >> >>So, what are 'cgs' and 'MKS' and how do the differ from 'SI' and 'the metric >>system'? > >cgs, is a length-mass-time system, with cm, g, s as the base units, it is not >widely used anymore, except perhaps in the US which I here actually even >uses Imperial units on occasion (I mean can you imagine!! (Flame me!) > >MKS (if I remember correctly) is a length-force-time system, where metre, (that Okay, before anyone else has the chance to flame me, let be the first! MKS is a length-mass-time system. (Boy I'd look to meet the fool who thought it was force ;-) So the question arises, what is the difference between MKS and SI. And before anyone else writes me telling me how great cgs is for Gaussian whatever, please note from the >> that I was following up a comment from sci.geo.geology. (sometimes I think the sci.space lot are from another planet or something! :-) > >Nicholas Fitzpatrick, Waterloo, Ontario, Canada ditto From gaetz@julian.uwo.ca Wed Jan 29 18:08:08 1992 Status: O X-VM-v5-Data: ([nil t nil nil nil nil nil nil nil] ["2871" "Tue" "28" "January" "1992" "03:31:27" "GMT" "Terry Gaetz" "gaetz@julian.uwo.ca " nil "60" "Re: SI Units vs cgs units" nil nil nil "1"]) Newsgroups: sci.astro,sci.geo.geology,sci.space From: gaetz@julian.uwo.ca (Terry Gaetz) Subject: Re: SI Units vs cgs units Organization: Dept. of Astronomy, Univ. of Western Ontario Date: Tue, 28 Jan 1992 03:31:27 GMT In article <1992Jan27.224415.9284@acsu.buffalo.edu> dmark@acsu.buffalo.edu (David Mark) writes: >>The metric system was originally designed to have convenient multiples >>of ten for every unit - grams, kilograms, gigagrams, meters, centimeters, >>micrometers, seconds, milliseconds, picoseconds. Why not use that which is >>convenient? I can remember the basic numbers (Planck's constant, mass >>of proton, etc.) in both MKS and cgs units. I use whichever is easier. >>It is trivial to convert. > >I'll ask the naive question; I hope I'm not the only sci.geo.geology >subscriber who doesn't know this! > >I thought I knew what the 'metric system' was, and also that SI was the >abbreviation for the scholarly or 'official' term for the metric system. > >So, what are 'cgs' and 'MKS' and how do the differ from 'SI' and 'the metric >system'? metric system: any decimal system of measures based on the metre (e.g. SI, cgs, MKS, MKSA); often SI is meant. cgs: system of units based on centimetres (cm), grams (g), and seconds (s). (also variants: electrostatic, electromagnetic, Gaussian, and Heaviside-Lorentz units, depending on the units used for electromagnetic quantities) MKS: system of units based on metres (m), kilograms (kg), and seconds (s). (variant: rationalized MKSA adds the ampere) SI: Syst\`eme International d'Unit\'es: m metre (length) kg kilogram (mass) s second (time) K kelvin (temperature interval) A ampere (electric current) cd candela (luminous intensity) mol mole (amount of substance) Other units are formed as combinations of these basic units and selected powers of ten. Permitted prefixes are E exa 10^(18) m milli 10^(-3) P peta 10^(15) \mu micro 10^(-6) T tera 10^(12) n nano 10^(-9) G giga 10^(9) p pico 10^(-12) M mega 10^(6) f femto 10^(-15) k kilo 10^(3) a atto 10^(-18) hecto (10^2), deca (10), deci (10^-1), and centi (10^-2) are allowed, but are to be used only where kilo- or milli- would be impractical. Thus, the centimetre (cm) is not a prefered SI unit. [the above is based on: appendix to Chambers English Dictionary, Jackson: "Classical Electrodynamics"] SI is the adopted international standard, but (Gaussian) cgs units and others (e.g. various forms of 'natural' units) are also widely used in astronomy and physics. -- Terry Gaetz -- gaetz@julian.uwo.ca "Without Units, dimensionless analysis itself would be impossible." (somebody's .sig; sorry, I don't have the attribution) From henry@zoo.toronto.edu Wed Jan 29 18:08:12 1992 Status: O X-VM-v5-Data: ([nil t nil nil nil nil nil nil nil] ["1736" "Tue" "28" "January" "1992" "17:17:08" "GMT" "Henry Spencer" "henry@zoo.toronto.edu " nil "29" "Re: SI Units vs cgs units" nil nil nil "1"]) Newsgroups: sci.astro,sci.geo.geology,sci.space From: henry@zoo.toronto.edu (Henry Spencer) Subject: Re: SI Units vs cgs units Date: Tue, 28 Jan 1992 17:17:08 GMT Organization: U of Toronto Zoology In article <1992Jan27.224415.9284@acsu.buffalo.edu> dmark@acsu.buffalo.edu (David Mark) writes: >I thought I knew what the 'metric system' was, and also that SI was the >abbreviation for the scholarly or 'official' term for the metric system. >So, what are 'cgs' and 'MKS' and how do the differ from 'SI' and 'the metric >system'? They're all metric systems. The question is, what is the unit of (say) energy? Is it kg-m^2/s^2, or g-cm^2/s^2, or what? And what is its name? In this case the units differ only by factors of ten, but the situation can be worse -- there are some electromagnetic units which might or might not have a factor of pi in them, for example, depending on what convention you choose. Over the years various groups chose various different sets of conventions, and the result was difficult and troublesome conversion problems when, say, a thermodynamicist wanted to talk to a magnet expert. You had to be careful even when the names seemed similar; for example, there were three or four subtly-different units named "calorie". SI, Systeme International, is an attempt to pull all this together and have *one* metric system, with *one* unit for expressing, say, magnetic flux density, and a consistent set of conversions with as few magic conversion factors as possible. Although SI is essentially universally accepted as desirable, the switchover was always expected to be a very long process, and indeed it is proving to be so. It takes an awfully long time to convert things like reference books, not to mention all the problems of equipment. -- "Breakthrough ideas are not | Henry Spencer @ U of Toronto Zoology >from teams." -- Hans von Ohain | henry@zoo.toronto.edu utzoo!henry From a722756@pan.mc.ti.com Wed Jan 29 18:08:13 1992 Status: O X-VM-v5-Data: ([nil t nil nil nil nil nil nil nil] ["1988" "Tue" "28" "January" "1992" "21:51:29" "GMT" "W. D. Rolph" "a722756@pan.mc.ti.com " nil "39" "Re: SI Units vs cgs units" nil nil nil "1"]) Newsgroups: sci.astro,sci.geo.geology,sci.space From: a722756@pan.mc.ti.com (W. D. Rolph) Subject: Re: SI Units vs cgs units Organization: Texas Instruments Materials and Controls Group Date: Tue, 28 Jan 1992 21:51:29 GMT henry@zoo.toronto.edu (Henry Spencer) writes: >In article <1992Jan27.224415.9284@acsu.buffalo.edu> dmark@acsu.buffalo.edu (David Mark) writes: >>I thought I knew what the 'metric system' was, and also that SI was the >>abbreviation for the scholarly or 'official' term for the metric system. >>So, what are 'cgs' and 'MKS' and how do the differ from 'SI' and 'the metric >>system'? >They're all metric systems. The question is, what is the unit of (say) >energy? Is it kg-m^2/s^2, or g-cm^2/s^2, or what? And what is its name? >In this case the units differ only by factors of ten, but the situation >can be worse -- there are some electromagnetic units which might or might >not have a factor of pi in them, for example, depending on what convention >you choose. Over the years various groups chose various different sets of >conventions, and the result was difficult and troublesome conversion >problems when, say, a thermodynamicist wanted to talk to a magnet expert. >You had to be careful even when the names seemed similar; for example, >there were three or four subtly-different units named "calorie". >SI, Systeme International, is an attempt to pull all this together and >have *one* metric system, with *one* unit for expressing, say, magnetic >flux density, and a consistent set of conversions with as few magic >conversion factors as possible. >Although SI is essentially universally accepted as desirable, the switchover >was always expected to be a very long process, and indeed it is proving >to be so. It takes an awfully long time to convert things like reference >books, not to mention all the problems of equipment. >-- >"Breakthrough ideas are not | Henry Spencer @ U of Toronto Zoology >from teams." -- Hans von Ohain | henry@zoo.toronto.edu utzoo!henry The wonders of the "standard" metric system. Now for grins is force in kilograms, or newtons or what? -- Regards. Don Rolph a722756@pan.mc.ti.com WD3 MS10-13 (508)-699-1263 From leb@gsfc.nasa.gov Wed Jan 29 18:08:14 1992 Status: O X-VM-v5-Data: ([nil t nil nil nil nil nil nil nil] ["3292" "" "29" "January" "92" "02:32:11" "GMT" "Lee E. Brotzman" "leb@gsfc.nasa.gov " nil "56" "Re: SI Units vs cgs units" nil nil nil "1"]) From: leb@gsfc.nasa.gov (Lee E. Brotzman) Newsgroups: sci.astro,sci.space Subject: Re: SI Units vs cgs units Date: 29 Jan 92 02:32:11 GMT Organization: Goddard Space Flight Center Nntp-Posting-Host: hypatia.gsfc.nasa.gov >henry@zoo.toronto.edu (Henry Spencer) writes: >>SI, Systeme International, is an attempt to pull all this together and >>have *one* metric system, with *one* unit for expressing, say, magnetic >>flux density, and a consistent set of conversions with as few magic >>conversion factors as possible. >>Although SI is essentially universally accepted as desirable, the switchover >>was always expected to be a very long process, and indeed it is proving >>to be so. It takes an awfully long time to convert things like reference >>books, not to mention all the problems of equipment. >>-- >>"Breakthrough ideas are not | Henry Spencer @ U of Toronto Zoology >>from teams." -- Hans von Ohain | henry@zoo.toronto.edu utzoo!henry I think that this thread has rapidly diverged from its original intent. This is sci.astro, and the discussion was about standardized units for use in astronomy. The International Astronomical Union has firmly come down on the side of SI units. I have spent my entire nine-year professional career providing data to the astronomical community under the auspices of the Astronomical Data Center at NASA Goddard Space Flight Center. In the early 80's, individual requesters were provided with one or two datasets on magnetic tape and wrote their own analysis routines to reduce the data. Now they can request large volumes of data over the networks or on CD-ROM and can access all of the data simultaneously. Intercomparison of the data is essential to modern data analysis, and that implies that the data should be in a common system of units. As a data archive, the ADC must be responsive to the requirements of our contributors and maintain the data in its original form as given. On the other hand, we must be responsive to our requesters and provide the data in the form they require to complete their work. The path that we chose was to select a standard nomenclature for the field names and for the units that those fields appeared in. The work that went into our CD-ROM of astronomical catalogs was mostly directed to standardizing the nomenclature of fields names and units. With a common set of field names (visual magnitude always V, hours of right acsension always RAH, etc.) and a common set of units (mag always magnitude, h always hours of time, etc.) it is possible to write software that can determine the correct operations to perform on a given datum. The promulgation of these standards is an important function of the international astronomical data centers and of the North American and European FITS committees. For further discussions of the standardized nomenclature proposed by the ADC, we suggest that you stay in touch with the sci.astro and alt.sci.astro.fits discussion groups. The ADC CD-ROM of astronomical catalogs is currently available from the National Space Science Data Center at NASA Goddard Space Flight Center, and complete information on how to obtain the data will be given in this forum as soon as the material is made available. -- -- Lee E. Brotzman Internet: brotzman@nssdca.gsfc.nasa.gov -- Hughes STX SPAN: NSSDCA::BROTZMAN -- National Space Science Data Center BITNET: ZMLEB@SCFVM -- NASA Goddard Space Flight Center From okunewck@psuvax1.cs.psu.edu Wed Jan 29 18:08:16 1992 Status: O X-VM-v5-Data: ([nil t nil nil nil nil nil nil nil] ["2144" "Wed" "29" "January" "1992" "18:07:46" "GMT" "Phil OKunewick" "okunewck@psuvax1.cs.psu.edu " nil "43" "Re: SI Units vs cgs units" nil nil nil "1"]) Newsgroups: sci.astro,sci.geo.geology,sci.space From: okunewck@psuvax1.cs.psu.edu (Phil OKunewick) Subject: Re: SI Units vs cgs units Nntp-Posting-Host: psuvax1.cs.psu.edu Organization: Random, at best Date: Wed, 29 Jan 1992 18:07:46 GMT This is an old debate. And a stupid one. The "metric" versus "traditional" measuring debate has been going on ever since the metric system was first introduced. Since the metric system is usually easier to use, it's gradually taking over. But so what?? If you can't handle all measurements currently used in your field (including those in still-useful old texts), then you probably should consider another line of work. The information is what's important, not the units it's expressed in. If you want to really improve things, then drop this stupid base-ten system. The factors are five and two. Two is okay, but what kind of a nut would want to work with fives? Oh sure - you say you're comfortable with bast ten. That's because it's been drummed into your head since you were a toddler - "Now junior, count to ten on your eight fingers and two thumbs..." But did you ever try to cut a pie into five slices? Damn near impossible. It's time to dump this nonsense, and start working with something clean. What's wrong with dividing by two's? Dividing a pie into four or eight slices is easy. Our entire civilization should start using Base-16 - it's a power of two that people can easily deal with. Measuring becomes infinitely simpler - start with a standard that's one unit long, and keep doubling it or dividing it in half. Heck, some cultures already do this - 1/8", 1/2", 1/32", pints, quarts, you get the idea. Each time you divide or multiply four times (see that power of two there?), you shift a decimal place. Simple as that. Still not convinced? Then consider the alternative - someday in the distant future we may encounter intelligent life in another part of the universe. And their first assessment of us will be, "Base-ten?? What kind of a numbering system is that? No wonder it took you earthlings so long to get into space - you spend all your time measuring and no time thinking. What a bunch of nimrods." And they'll tell all their buddies, and earthlings will become the laughing stock of the universe. Now we don't really want that that to happen, do we? I think not. From gill@physics.ubc.ca Wed Jan 29 18:08:20 1992 Status: O X-VM-v5-Data: ([nil t nil nil nil nil nil nil nil] ["1320" "" "29" "January" "92" "21:43:49" "GMT" "Arnold Gill visiting astrophys phd std" "gill@physics.ubc.ca " nil "31" "Re: SI Units vs cgs units" nil nil nil "1"]) From: gill@physics.ubc.ca (Arnold Gill visiting astrophys phd std) Newsgroups: sci.astro,sci.geo.geology,sci.space Subject: Re: SI Units vs cgs units Date: 29 Jan 92 21:43:49 GMT Organization: University of British Columbia, Vancouver, B.C., Canada Nntp-Posting-Host: physics.ubc.ca okunewck@psuvax1.cs.psu.edu (Phil OKunewick) writes: > If you can't handle all measurements currently used in your field >(including those in still-useful old texts), then you probably should >consider another line of work. The information is what's important, >not the units it's expressed in. Quite agreed - but it makes things easier if future generations didn't have to worry about what units a specific quantity is measured in. Of course, if you want really strange units, then look at some GR or QM papers where all of the standard constants are equal to 1. > If you want to really improve things, then drop this stupid >base-ten system. The factors are five and two. Two is okay, but what >kind of a nut would want to work with fives? [...and...] > Our entire civilization should start using Base-16 - it's a power >of two that people can easily deal with. I've read novels which were of the opinion that the most sensible base is actually base 12 -- a small number tht has lots of small factors (2,3,4,6). Potentially more useful. However, its not going to happen, and base 16 is only useful for computers and people who can only say "Yes" and "No". :-) -- Arnold Gill --- astrophysician trainee in exile gill@physics.ubc.ca From dsc@gemini.tmc.edu Wed Jan 29 18:08:22 1992 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["1879" "" "28" "January" "92" "14:57:43" "GMT" "Doug S. Caprette Bldg. 28 W191 x3892" "dsc@gemini.tmc.edu " nil "33" "SI Units vs others" "^From:" nil nil "1"]) Newsgroups: sci.astro,sci.geo.geology,sci.space Organization: NASA GSFC CDP VLBI Nntp-Posting-Host: gemini.gsfc.nasa.gov From: dsc@gemini.tmc.edu (Doug S. Caprette Bldg. 28 W191 x3892) Subject: SI Units vs others Date: 28 Jan 92 14:57:43 GMT In article <1992Jan28.005635.14025@watserv1.waterloo.edu> nick@sunburn.waterloo.edu (Nick Fitzpatrick) writes: > >cgs, is a length-mass-time system, with cm, g, s as the base units, it is not >widely used anymore, except perhaps in the US which I here actually even >uses Imperial units on occasion (I mean can you imagine!! (Flame me!) > The units customarily used by engineers in the US are properly refered to as American Customary Units (ACU). They include some SI and other metric units, as well as some Imperial units, and some uniquely American units e.g. the gallon. There are also some bizarre 'hybrid' units like the kip (kilopound). This kind of thing seems to be very poorly organized to the layman, but ACU are chosen to yield values in a reasonable range for everyday use. In particular, the use of a system based on unit force, (the pound) is advantageous when doing analysis of stress and strain. This probably dates back to slide rule days. Bear in mind that the principle advantage to metric units is the simplifi- cation of arithmetic, an advantage largely gone since the proliferation of the electronic calculator. It seems only reasonable for people to publish results in the units in which the work is customarily done. As an aside, why is the angstrom considered an oddball unit? Ten, raised to the power of negative ten is about as metric as you can get. Ten, raised to the power of negative nine, should be considered odd. After all, nine is NOT an integral multiple of ten. -- | Regards, | Hughes STX | Code 926.9 GSFC | | Doug Caprette | Lanham, Maryland | Greenbelt, MD 20771 | ------------------------------------------------------------------------------- "Le guard meurte, mais ne se donne pas." -- (falsely?) attributed to General Cambronne at Waterloo From nick@sunburn.waterloo.edu Wed Jan 29 18:08:23 1992 Status: O X-VM-v5-Data: ([nil t nil nil nil nil nil nil nil] ["1917" "" "28" "January" "92" "21:37:10" "GMT" "Nick Fitzpatrick" "nick@sunburn.waterloo.edu " nil "31" "Re: SI Units vs others" nil nil nil "1"]) From: nick@sunburn.waterloo.edu (Nick Fitzpatrick) Newsgroups: sci.astro,sci.geo.geology,sci.space Subject: Re: SI Units vs others Date: 28 Jan 92 21:37:10 GMT Organization: University of Waterloo In article <1992Jan28.145743.23033@nsisrv.gsfc.nasa.gov> dsc@gemini.tmc.edu (Doug S. Caprette Bldg. 28 W191 x3892) writes: >In article <1992Jan28.005635.14025@watserv1.waterloo.edu> nick@sunburn.waterloo.edu (Nick Fitzpatrick) writes: >> >>cgs, is a length-mass-time system, with cm, g, s as the base units, it is not >>widely used anymore, except perhaps in the US which I here actually even >>uses Imperial units on occasion (I mean can you imagine!! (Flame me!) >> >The units customarily used by engineers in the US are properly refered to >as American Customary Units (ACU). They include some SI and other metric >units, as well as some Imperial units, and some uniquely American units >e.g. the gallon. There are also some bizarre 'hybrid' units like the >kip (kilopound). This kind of thing seems to be very poorly organized >to the layman, but ACU are chosen to yield values in a reasonable range >for everyday use. In particular, the use of a system based on unit force, >(the pound) is advantageous when doing analysis of stress and strain. >This probably dates back to slide rule days. > Yes it is very frustating when one comes along a US publication, where they indicate concentrations in mg/L, and then present flows in USgal/day (ACK, ugh, painful), where if the units were in L/day (or m^3/day) any fool can immediatly see that the flux is. Pounds for stress? The problems that get me with Imperial, is that some people used pound force, and erg for mass (or was it slug, some dead unit, I have to check it every time) and some used pound mass, and poundal force. I'm not sure how one would use pound stress, surely you would need a force/area unit, like Pascals or something . . . I suppose the one advantage we got in the Free trade pact with the US, was that it provided protection for the (Canadian) metric system, however there was no protection for the US system. (Thank the lord, ) From dsc@gemini.tmc.edu Wed Jan 29 18:08:27 1992 Status: O X-VM-v5-Data: ([nil t nil nil nil nil nil nil nil] ["1614" "" "29" "January" "92" "00:21:37" "GMT" "Doug S. Caprette Bldg. 28 W191 x3892" "dsc@gemini.tmc.edu " nil "31" "Re: SI Units vs others" nil nil nil "1"]) From: dsc@gemini.tmc.edu (Doug S. Caprette Bldg. 28 W191 x3892) Newsgroups: sci.astro,sci.geo.geology,sci.space Subject: Re: SI Units vs others Date: 29 Jan 92 00:21:37 GMT Organization: NASA GSFC CDP VLBI Nntp-Posting-Host: gemini.gsfc.nasa.gov In article <1992Jan28.213710.7334@watserv1.waterloo.edu> nick@sunburn.waterloo.edu (Nick Fitzpatrick) writes: >In article <1992Jan28.145743.23033@nsisrv.gsfc.nasa.gov> dsc@gemini.tmc.edu (Doug S. Caprette Bldg. 28 W191 x3892) writes: >> ... >>for everyday use. In particular, the use of a system based on unit force, >>(the pound) is advantageous when doing analysis of stress and strain. >>This probably dates back to slide rule days. >> >Yes it is very frustating when one comes along a US publication, where >they indicate concentrations in mg/L, and then present flows in >USgal/day (ACK, ugh, painful), where if the units were in L/day (or m^3/day) >any fool can immediatly see that the flux is. > >Pounds for stress? The problems that get me with Imperial, is that > Of course not (layman). PSI for stress, or, kPSI (kilopounds per square inch). The pound (force) is a basic unit in ACU. The unit of mass (slug), is a derived unit, as are pressure units. > >some people used pound force, and erg for mass (or was it slug, some > Erg is a metric unit (cgs: gm cm squared per second squared). A slug is that mass which accelerates at a rate of one foot per second squared when acted on by a force of one pound. > >dead unit, I have to check it every time) and some used pound >mass, and poundal force. I'm not sure how one would use pound stress, surely >you would need a force/area unit, like Pascals or something . . . > You need a hell of a lot of them in fact, 350,150 or so Pascals for normal atmospheric pressure at sea level and Mega or even Giga Pascals for real world stresses and pressures. From nick@sunburn.waterloo.edu Wed Jan 29 18:08:32 1992 Status: O X-VM-v5-Data: ([nil t nil nil nil nil nil nil nil] ["1243" "Wed" "29" "January" "1992" "03:15:32" "GMT" "Nick Fitzpatrick" "nick@sunburn.waterloo.edu " nil "26" "Re: SI Units vs others" nil nil nil "1"]) Newsgroups: sci.astro,sci.geo.geology,sci.space From: nick@sunburn.waterloo.edu (Nick Fitzpatrick) Subject: Re: SI Units vs others Organization: University of Waterloo Date: Wed, 29 Jan 1992 03:15:32 GMT In article <1992Jan29.002137.20487@nsisrv.gsfc.nasa.gov> dsc@gemini.tmc.edu (Doug S. Caprette Bldg. 28 W191 x3892) writes: >>you would need a force/area unit, like Pascals or something . . . >> >You need a hell of a lot of them in fact, 350,150 or so Pascals for normal >atmospheric pressure at sea level and Mega or even Giga Pascals for real >world stresses and pressures. Well of course you dont just use Pa (duhhh). Anyone who has ever checked the weather forecast in this country (Canada) will see the pressure listed as 101.3 kPa (or something close, depending on the weather), pretty simple atmospheric pressure = (about) 100 kPa. Simple. And when we get into engineering we use MPa, therefore, in Canada, a normal concrete is rated at (I believe) 20 MPa. Thats the whole beauty of Metric, the prefixes. I go from Montreal to Toronto, 500 km My height 1.75 m. My pencil lead, 5mm. and then we get all those microscopic things. God when I see those US papers, I just die, volume in ft^3, volume in fl oz, volume in ft^2*acre, volume in gal (US), volume in gal (IMP) volume in pints, volume in quarts, volume in bushels. God I could just die, it so weird, How anyone is supposed to get an intuitive feel for it I don't know. From bthoen@teal.csn.org Wed Jan 29 18:08:33 1992 Status: O X-VM-v5-Data: ([nil t nil nil nil nil nil nil nil] ["1519" "" "29" "January" "92" "04:27:45" "GMT" "Bill Thoen" "bthoen@teal.csn.org " nil "28" "Re: SI Units vs others" nil nil nil "1"]) From: bthoen@teal.csn.org (Bill Thoen) Newsgroups: sci.astro,sci.geo.geology,sci.space Subject: Re: SI Units vs others Date: 29 Jan 92 04:27:45 GMT Organization: Colorado SuperNet, Inc. Nntp-Posting-Host: teal.csn.org In article <1992Jan29.031532.14841@watserv1.waterloo.edu> nick@sunburn.waterloo.edu (Nick Fitzpatrick) writes: > >God when I see those US papers, I just die, volume in ft^3, volume in >fl oz, volume in ft^2*acre, volume in gal (US), volume in gal (IMP) >volume in pints, volume in quarts, volume in bushels. God I could just >die, it so weird, How anyone is supposed to get an intuitive feel for >it I don't know. Well, it used to be even worse. In "A New and Complete System of Arithmetic Composed for the Use of the Citizens of the United States" by Nicholas Pike, A.M. published in 1797, you can see that we (Americans) have made some improvements. For example, back then 7 92/100 inches was one link, 25 links made one 1 pole, 4 poles made one chain, 10 chains made one furlong, 8 furlongs were in every mile. And another inportant measure was for beer. We still have the quart and gallon, but did you know that 8 gallons make a firkin? And 2 firkins make a kilderkin, and 2 kilderkins made a barrel, and 1 1/2 barrels made a hogshead, 2 barrels equals a puncheon, and there was 3 barrels to the butt. It goes on and on for all kinds of measures, and there was even exchange rates for money between the various states! So when you read American papers, you should count your blessings that this isn't 1797 anymore, eh? :-) (The above information is mentioned in a more recent book by Isaac Asimov, "Asimov on Numbers", 1977 edition by Pocket Books, ISBN 0-671-82134-2) - Bill Thoen bthoen@csn.org From henry@zoo.toronto.edu Wed Jan 29 18:08:35 1992 Status: O X-VM-v5-Data: ([nil t nil nil nil nil nil nil nil] ["1056" "Wed" "29" "January" "1992" "05:27:31" "GMT" "Henry Spencer" "henry@zoo.toronto.edu " nil "19" "Re: SI Units vs others" nil nil nil "1"]) Newsgroups: sci.astro,sci.geo.geology,sci.space From: henry@zoo.toronto.edu (Henry Spencer) Subject: Re: SI Units vs others Date: Wed, 29 Jan 1992 05:27:31 GMT Organization: U of Toronto Zoology In article <1992Jan29.002137.20487@nsisrv.gsfc.nasa.gov> dsc@gemini.tmc.edu (Doug S. Caprette Bldg. 28 W191 x3892) writes: >... The pound (force) is a basic unit in ACU. The unit of mass (slug), >is a derived unit, as are pressure units. And of course, when you receive a hardware weight estimate in pounds, it has to be converted to slugs before you can do anything with it. >You need a hell of a lot of them in fact, 350,150 or so Pascals for normal >atmospheric pressure at sea level and Mega or even Giga Pascals for real >world stresses and pressures. Yawn. So what else is new? The farad (unit of capacitance) is at the other end of the scale, far too large for most practical purposes, so electronics types have been using pF, nF, and uF for a long time. It is not difficult. Normal atmospheric pressure is about 100 kPa; where did you get 350? Mess up a conversion factor? :-) -- "Breakthrough ideas are not | Henry Spencer @ U of Toronto Zoology >from teams." -- Hans von Ohain | henry@zoo.toronto.edu utzoo!henry From binkley@boulder.Colorado.EDU Wed Jan 29 18:08:36 1992 Status: O X-VM-v5-Data: ([nil t nil nil nil nil nil nil nil] ["738" "" "29" "January" "92" "06:58:09" "GMT" "Jon Binkley" "binkley@boulder.Colorado.EDU " nil "20" "Re: SI Units vs others" nil nil nil "1"]) From: binkley@boulder.Colorado.EDU (Jon Binkley) Newsgroups: sci.astro,sci.geo.geology,sci.space Subject: Re: SI Units vs others Date: 29 Jan 92 06:58:09 GMT Organization: University of Colorado, Boulder Nntp-Posting-Host: beagle.colorado.edu Say what will about the Imperial System, but I learned of a cosmic coincidence which revived it in my mind. Don't even ask me how this inquiry came about, but it turns out that the cubic attoparsec (atto = e-18) is almost exactly equal to one fluid ounce (certainly to within the error of accurately measuring an attoparsec!). Now, would you rather live in the cold, heartless world where your cubic attoparsecs equaled 0.029 something litres, or the warm, friendly world where your cubic attoparsecs equaled one nice round fluid ounce? Jon Binkley The conversion, for those who are as geeky as myself: 1 parsec = 3.09e13 km = 3.09e18 cm 1 attoparsec = 3.09 cm 1 cubic attoparsec = 29.5 cubic cm = 0.998 fl. oz. Close enough for me! From sacass@unix1.tcd.ie Wed Jan 29 18:08:50 1992 Status: O X-VM-v5-Data: ([nil t nil nil nil nil nil nil nil] ["1149" "" "29" "January" "92" "11:45:44" "GMT" "stephen andrew cass" "sacass@unix1.tcd.ie " nil "20" "Re: SI Units vs others" nil nil nil "1"]) From: sacass@unix1.tcd.ie (stephen andrew cass) Newsgroups: sci.astro,sci.geo.geology,sci.space Subject: Re: SI Units vs others Date: 29 Jan 92 11:45:44 GMT Organization: Trinity College, Dublin Nntp-Posting-Host: unix1.tcd.ie In binkley@boulder.Colorado.EDU (Jon Binkley) writes: >Don't even ask me how this inquiry came about, but it turns out that >the cubic attoparsec (atto = e-18) is almost exactly equal to >one fluid ounce (certainly to within the error of accurately >measuring an attoparsec!). >Now, would you rather live in the cold, heartless world where >your cubic attoparsecs equaled 0.029 something litres, or the >warm, friendly world where your cubic attoparsecs equaled one >nice round fluid ounce? Sorry, but what is an ounce? Those of us brought up in the brave new world of the metric system simply have very little real conception of what the Imperial units ARE inside our heads. If someones says something is 4 pounds for example, I will have no *real* understanding of the weight untill I run some kind of conversion. For me I think of Yards as short meters, and have a reasonable idea of inches and miles and pints, but after that I really have no idea of imperial measures. I *KNOW* what a litre is, but the same cannot be said of an ounce. Does anyone else out there feel the same? Stephen Cass ( sacass@unix1.tcd.ie) From nareid@imf.unit.no Wed Jan 29 18:08:52 1992 Status: O X-VM-v5-Data: ([nil t nil nil nil nil nil nil nil] ["1029" "" "29" "January" "92" "14:18:53" "GMT" "Helge Nareid" "nareid@imf.unit.no " nil "22" "Re: SI Units vs others" nil nil nil "1"]) From: nareid@imf.unit.no (Helge Nareid) Newsgroups: sci.astro,sci.geo.geology,sci.space Subject: Re: SI Units vs others Date: 29 Jan 92 14:18:53 GMT Organization: The Norwegian Institute of Technology, Trondheim In article sacass@unix1.tcd.ie (stephen andrew cass) writes: >In binkley@boulder.Colorado.EDU (Jon Binkley) writes: >>Don't even ask me how this inquiry came about, but it turns out that >>the cubic attoparsec (atto = e-18) is almost exactly equal to >>one fluid ounce (certainly to within the error of accurately >>measuring an attoparsec!). >Sorry, but what is an ounce? Those of us brought up in the brave new >world of the metric system simply have very little real conception of >what the Imperial units ARE inside our heads. >Stephen Cass ( sacass@unix1.tcd.ie) And exactly what sort of fluid ounce is it - an imperial fluid ounce (28.413 ml) or a US fluid ounce (29.574 ml) ??? Or is there a difference between the US and UK parsec ? -- Helge Nareid E-mail : nareid@phys.unit.no SINTEF Applied Physics Phone : + 47 - 7 - 59 34 18 Trondheim, Norway Fax : + 47 - 7 - 59 34 20 From jkohnen@comix.cs.uoregon.edu Wed Jan 29 18:08:53 1992 Status: O X-VM-v5-Data: ([nil t nil nil nil nil nil nil nil] ["1338" "" "28" "January" "92" "22:18:41" "GMT" "John Hamilton Kohnen" "jkohnen@comix.cs.uoregon.edu " nil "25" "Re: SI Units vs others" nil nil nil "1"]) From: jkohnen@comix.cs.uoregon.edu (John Hamilton Kohnen) Newsgroups: sci.astro,sci.geo.geology,sci.space Subject: Re: SI Units vs others Date: 28 Jan 92 22:18:41 GMT Organization: The Max Robinson Institute "This kind of thing seems to be very poorly organized to the layman, but ACU are chosen to yield values in a reasonable range for everyday use." Producing values in a reasonable range for everyday use is the key to choosing any system of measure. For virtually all of us that means most of the time there are only three units: too little, too much, and just right. A rational hierarchical scheme is simply unnecessary to function in regular society. Traditional units like feet-yards-miles, far from being as irrational as is usually thought, are firmly grounded on this principle. Consider the beer drinking English and their traditional fluid measures, the ounce, pint, and quart. An ounce is what one can normally swallow easily and the pint about what is comfortable to raise in one hand. Two pints, or a quart, and you have a pleasant time with your chums, not too much and not too little. Imminently sensible. But what if you are on the continent and must use the metric system? Clearly a cubic centimeter won't satisfy anybody but the company chemist, so your recourse is the liter. Larger even than a quart and too much for one hand, that's a unit provocative of athletic drinking. Little wonder both the French and the Germans have tried to conquer the whole of Europe since metric units were adopted. From davem@ee.ubc.ca Thu Jan 30 09:48:36 1992 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["240" "Thu" "30" "January" "1992" "00:59:48" "GMT" "david michelson" "davem@ee.ubc.ca " nil "6" "Re: SI Units vs cgs units" "^From:" nil nil "1"]) Newsgroups: sci.astro,sci.geo.geology,sci.space Organization: University of BC, Electrical Engineering From: davem@ee.ubc.ca (david michelson) Subject: Re: SI Units vs cgs units Date: Thu, 30 Jan 1992 00:59:48 GMT Well, I for one don't like cgs *at all*. I mean, how can anyone like a system where capacitance is measured in units of *length*! :-) Dave Michelson "davem@ee.ubc.ca" UBC Electrical Engineering Applied Electromagnetics Group From jokim@jarthur.claremont.edu Thu Jan 30 09:49:16 1992 Status: O X-VM-v5-Data: ([nil t nil nil nil nil nil nil nil] ["1298" "" "30" "January" "92" "03:26:23" "GMT" "John H. Kim" "jokim@jarthur.claremont.edu " nil "28" "Re: SI Units vs cgs units" nil nil nil "1"]) From: jokim@jarthur.claremont.edu (John H. Kim) Newsgroups: sci.astro,sci.geo.geology,sci.space Subject: Re: SI Units vs cgs units Date: 30 Jan 92 03:26:23 GMT Followup-To: sci.astro,sci.geo.geology,sci.space Organization: Harvey Mudd College, Claremont, CA 91711 In article <1992Jan28.033127.22112@julian.uwo.ca> gaetz@julian.uwo.ca (Terry Gaetz) writes: >SI: Syst\`eme International d'Unit\'es: > m metre (length) > kg kilogram (mass) > s second (time) > K kelvin (temperature interval) > A ampere (electric current) > cd candela (luminous intensity) > mol mole (amount of substance) > Other units are formed as combinations of these basic units > and selected powers of ten. Permitted prefixes are .... > k kilo 10^(3) a atto 10^(-18) Except, because they made converting between units so much easier than the english system, they decided to slip in KILO-grams just to keep everyone on their toes. Be careful of this if you've got a whole mess of numbers and units and you try to simplify it by canceling out prefixes like 'kilo' and 'Mega' when they're in both the numerator and denominator. (If you're careful, you'll notice you have grams left over, not kg, but more often you'll end up reading it as kg) -- John H. Kim | (This space to be filled when I jokim@jarthur.claremont.edu | think of something very clever uunet!jarthur!jokim | to use as a disclaimer) From userDHAL@mts.ucs.UAlberta.CA Thu Jan 30 09:51:13 1992 Status: O X-VM-v5-Data: ([nil t nil nil nil nil nil nil nil] ["1868" "" "30" "January" "92" "00:33:54" "GMT" "David Halliwell" "userDHAL@mts.ucs.UAlberta.CA " nil "41" "Re: SI Units vs others" nil nil nil "1"]) From: userDHAL@mts.ucs.UAlberta.CA (David Halliwell) Newsgroups: sci.astro,sci.geo.geology,sci.space Subject: Re: SI Units vs others Date: 30 Jan 92 00:33:54 GMT Organization: MTS Univ of Alberta In article <1992Jan29.031532.14841@watserv1.waterloo.edu>, nick@sunburn.waterloo.edu (Nick Fitzpatrick) writes: > >God when I see those US papers, I just die, volume in ft^3, volume in >fl oz, volume in ft^2*acre, volume in gal (US), volume in gal (IMP) >volume in pints, volume in quarts, volume in bushels. God I could just >die, it so weird, How anyone is supposed to get an intuitive feel for >it I don't know. I have to agree with this one. One of the areas I work in involves heat conduction. Have you ever seen the units that show of for thermal conductivity? The worst one I can remember was one where the flux density was in BTUs per square foot per second, and the temperature gradient was in Fahrenheit degrees per inch. Put the two linear measures into the same units? No way, Jose! It was left as such, giving thermal conductivity in, wait... (BTU/sq.ft./sec)/(deg.F/inch) (In SI units, thermal conductivity is W/mK. Which is simpler? :-)) And I'm glad that someone else has pointed out the difference between Imperial fluid ounces and U.S. fluid ounces. That's one of my favourite cocktail party pro-metric conversation pieces. It sometimes takes a LONG time to convince people of that one! By the way, is there anyone else out there who believes that stresses should be left as N/sq.m, and that Pa should be used ONLY for pressure? And now just for fun, the proverbial question (which I will leave unanswered for now): Which weighs more? A pound of gold, or a pound of feathers? Dave Halliwell | "Learn from the mistakes of others; Department of Geography | you'll not live long enough to make University of Alberta | them all yourself..." Edmonton, Alberta. | - Canada Aviation Safety Letter. From henry@zoo.toronto.edu Thu Jan 30 14:53:13 1992 Status: O X-VM-v5-Data: ([nil t nil nil nil nil nil nil nil] ["886" "Thu" "30" "January" "1992" "18:47:57" "GMT" "Henry Spencer" "henry@zoo.toronto.edu " nil "14" "Re: SI Units vs cgs units" nil nil nil "1"]) Newsgroups: sci.astro,sci.geo.geology,sci.space From: henry@zoo.toronto.edu (Henry Spencer) Subject: Re: SI Units vs cgs units Date: Thu, 30 Jan 1992 18:47:57 GMT Organization: U of Toronto Zoology In article gill@physics.ubc.ca (Arnold Gill visiting astrophys phd std) writes: > Of course, if you want really strange units, then look at some > GR or QM papers where all of the standard constants are equal to 1. An amusing side note on this: in his JBIS paper on space warps (real ones supported by current physics, not science-fictional ones), Robert Forward complained loudly about this convention. It makes the physics easier, but translating the results back into normal units -- so you can decide whether the engineering required is impossible or merely daunting -- is tremendously difficult because it's hard to figure out where (and which) conversion factors are needed. -- "Breakthrough ideas are not | Henry Spencer @ U of Toronto Zoology >from teams." -- Hans von Ohain | henry@zoo.toronto.edu utzoo!henry From paulz@hpspdla.spd.HP.COM Thu Jan 30 17:28:12 1992 Status: O X-VM-v5-Data: ([nil t nil nil nil nil nil nil nil] ["1121" "" "30" "January" "92" "01:19:42" "GMT" "Paul Zander" "paulz@hpspdla.spd.HP.COM " nil "27" "Re: Re: SI Units vs cgs units" nil nil nil "1"]) From: paulz@hpspdla.spd.HP.COM (Paul Zander) Newsgroups: sci.astro Subject: Re: Re: SI Units vs cgs units Date: 30 Jan 92 01:19:42 GMT Organization: HP Stanford Park - Palo Alto, CA henry@zoo.toronto.edu (Henry Spencer) writes: >The wonders of the "standard" metric system. Now for grins is force in >kilograms, or newtons or what? For the benefit of readers who don't know the answer: Kilograms is a unit of mass. A kilogram will be a kilogram on the earth, the moon, or deep space. If there is some gravitational field, a balance scale and a set of calibrated standards (popularly but incorrectly called "weights") might be used to determine mass. This works because in a scale is balanced, equal masses will have equal weights. One type of force is the gravitational attraction of the earth (moon, etc) on an object. Force can be measured by a spring scale. An object with a mass of 1 kilogram will have a weight of 1 newton on the earth's surface. The weight will be different in different places in the universe, but the mass is constant (ignoring relativistic effects). The difference between mass and force seems subtle to many beginning physics students, but is especially important in astronomy. More detailed coverage can be found in almost elementary physics text. Paul Zander From stefano@orion.astro.uiuc.edu Thu Jan 30 18:15:19 1992 Status: O X-VM-v5-Data: ([nil t nil nil nil nil nil nil nil] ["1087" "" "30" "January" "92" "20:21:40" "GMT" "Stefano Casertano" "stefano@orion.astro.uiuc.edu " nil "24" "Re: SI Units vs cgs units" nil nil nil "1"]) From: stefano@orion.astro.uiuc.edu (Stefano Casertano) Newsgroups: sci.astro Subject: Re: SI Units vs cgs units Date: 30 Jan 92 20:21:40 GMT Organization: University of Illinois at Urbana In <12990031@hpspdla.spd.HP.COM> paulz@hpspdla.spd.HP.COM (Paul Zander) writes: > (deleted about difference between mass and force) >One type of force is the gravitational attraction of the earth (moon, >etc) on an object. Force can be measured by a spring scale. An >object with a mass of 1 kilogram will have a weight of 1 newton on the ^^^^^^^^ >earth's surface. The weight will be different in different places in >the universe, but the mass is constant (ignoring relativistic >effects). No. It will have a weight equal to the mass times the local gravitational acceleration, typically about 9.81 m s^-2. Since the newton (N) equals 1 kg m s^-2, the weigth of a mass of one kg will be around 9.81 N, and it will be slightly different at different places on the Earth's surface. I commend your effort to clarify the difference between mass and weight, better than I could do (and I have tried in the past...) but please make sure of your facts next time... Stefano Casertano stefano@sirius.astro.uiuc.edu From joe@astro.as.utexas.edu Fri Jan 31 09:40:27 1992 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["163" "" "30" "January" "92" "21:07:48" "GMT" "Joe Wang" "joe@astro.as.utexas.edu " nil "5" "Re: SI Units (was Re: AAS meeting, Atlanta)" "^From:" nil nil "1"]) Newsgroups: sci.astro Distribution: sci Organization: McDonald Observatory, University of Texas @ Austin From: joe@astro.as.utexas.edu (Joe Wang) Subject: Re: SI Units (was Re: AAS meeting, Atlanta) Date: 30 Jan 92 21:07:48 GMT Speaking of which, my undergraduate training (only two years ago) was completely in cgs units, which meant that I was in for a shock when I took the GRE. OUCH!!! From paulz@hpspdla.spd.HP.COM Fri Jan 31 14:32:53 1992 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["368" "" "30" "January" "92" "21:45:38" "GMT" "Paul Zander" "paulz@hpspdla.spd.HP.COM " nil "9" "Re: Re: SI Units vs cgs units" "^From:" nil nil "1"]) Newsgroups: sci.astro Organization: HP Stanford Park - Palo Alto, CA From: paulz@hpspdla.spd.HP.COM (Paul Zander) Subject: Re: Re: SI Units vs cgs units Date: 30 Jan 92 21:45:38 GMT Correction: In my previous comments, there was an error. On the earth's surface, a mass of 1 kilogram will have a weight of 9.8 Newtons. That is because the earths gravitaional field creates an acceleration of 9.8 meters/second. The key point remains, mass is unaffected by gravity (ignoring relativistic effects) but weight is very much a function of gravity. From mehr@oskar.uchicago.edu Mon Feb 3 09:55:16 1992 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["852" "" "1" "February" "92" "00:56:01" "GMT" "David Mehringer" "mehr@oskar.uchicago.edu " nil "22" "Re: Re: SI Units vs cgs units" "^From:" nil nil "2"]) Newsgroups: sci.astro Organization: Department of Statistics From: mehr@oskar.uchicago.edu (David Mehringer) Subject: Re: Re: SI Units vs cgs units Date: 1 Feb 92 00:56:01 GMT In article <12990032@hpspdla.spd.HP.COM> paulz@hpspdla.spd.HP.COM (Paul Zander) writes: >Correction: > >In my previous comments, there was an error. On the earth's surface, a >mass of 1 kilogram will have a weight of 9.8 Newtons. That is because >the earths gravitaional field creates an acceleration of 9.8 >meters/second. > As long as we are being dimensionally correct, acceleration is measured in meters/(second)**2 in the mks system, not meters/second. >The key point remains, mass is unaffected by gravity (ignoring >relativistic effects) but weight is very much a function of gravity. The Newtonian relationship is weight = mass * gravity. -- Dave Mehringer | "There is a fine line between dignity and dmehring@zia.aoc.nrao.edu | stupidity." National Radio Astronomy | -- Homey the Clown Observatory, Socorro, NM | From cbm@mrcnext.cso.uiuc.edu Mon Feb 3 09:56:33 1992 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["758" "" "1" "February" "92" "18:35:28" "GMT" "Commodore Unix Support" "cbm@mrcnext.cso.uiuc.edu " nil "14" "Re: SI Units vs others" "^From:" nil nil "2"]) Newsgroups: sci.astro,sci.geo.geology,sci.space Organization: University of Illinois at Urbana From: cbm@mrcnext.cso.uiuc.edu (Commodore Unix Support) Subject: Re: SI Units vs others Date: 1 Feb 92 18:35:28 GMT dan@rcdips.nrl.navy.mil (Dan Nagle) writes: >If your car uses (say) 30 mpg, how many yards is that to the ounce? >(Ignore, if you are sure you can, the issue of WHICH ounce...) >Of course, if you only knew how many kilometers per liter, the >conversion to meters per milliliter is (ahem) straightforward. Of course, any physicist would represent it as meters per cubic meter and cancel, giving a mileage estimate of 0.0042 m^-2. Lets see. Inverse meters squared is inverse area, so we could really call it 0.0000432 acres^-1 or 0.0000432 erca's. Better yet, subatomic physicists would want to use barns for area, and represent it as 478329432 barns^-1, or 478329432 nrab's. Now why dont we just use those convenient units on the gas mileage estimates?