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Re: SI Metric

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On Jan 1, 2006, at 11:17 AM, Paul Ransom wrote:

No. The force-mass unit confusion does not exist in the "SI" measure.
That doesn't square with the hundreds of times I've seen forces quoted in in Kg and pressures and stresses in kg/mm^2. It's fair to say that there is no confusion inherent in either units system. The confusion lies in in the distinction between gravity force and mass and the failure to keep them separate in thinking. Someone sees a weight quoted in lb, thinks it's a mass and gets the two confused. Same as when someone looks at a mass of 100 kg break a rope and calls the breaking strength of the rope is 100 kg. The confusion isn't the units system--it's failure to think precisely.

As a result, we have slugs (ptuuiii) and commercial
measurement standards by goverment decree that define pounds as mass -
not lb-force associated with a mass, etc.
Naming a derived mass unit a slug isn't any sillier than naming a derived force unit a Newton. To be honest, I really don't care how many times you can cite some official or semi-official use of the term 'pound,' as anything besides a force. There's no confusion if you know your physics.

I'm a bit wounded at being included amongst your SI 'naysayers'--I was doing optical experiments in mm before most of the people on this list were born, and converting between chemical and electrical measures in the metric system and mechanical equivalents in US customary not long after that. The system I use for arithmetic is a matter of the profoundest indifference--Henry Beauclerc's arm is no more artificial and arbitrary a basis for measure as some Frenchman's guess at the circumference of the earth. What does matter to everyone are the resulting manufacturing standards--fasteners, pipe, shafting, metal gauging and thousands of others--10's of thousands if you distinguish the underlying measurement system. Centering on arithmetic or the problems of a technically illiterate laity really trivializes the discussion.


Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw(--nospam--at)skypoint.com   | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw/


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