I was in engineering college from 76 to 81 and remember some discussion about this. Fortunately there was not too much to discuss as they had already decided that SI was the way to go and we had recently selected "new" books. At the same time the "metric" revolution was in full swing and they were changing out all of their machine tools in the school shop so they would all be metric. They were removing manual machines that were setup in inches and replacing them with machines setup in millimeters. Many of the machines were old so I was happy to see them go and be replaced with new machines. The school was very unique in that they encouraged students to use the machines and the facilities after hours. They had a shop supervisor who was paid to stay late most weekday nights. Even the garage was available, so we could put our cars on the lifts to do repairs and modifications. When I wasn't chasing girls, I "lived" at school. :-)
Dave On 6/16/2012 3:22 AM, Peter Blodow wrote: > Andy, > way back in my school time, curriculum makers detected that mass and > force are different things. Before, forces were expressed in mass units, > i.e., kilogramms (greek: chilioi = thousand, gramma = weight), and > sometimes called kilogrammforce, which gives roughly identical figures > for computations as long as we are on earth. To signify the difference, > though, these force units were then called kiloponds (abbreviated kp, > latin: pondus = weight). > > To comply with international SI units, they abandoned this unit soon > (right after I had to learn it in school) and introduced the Newton as > the official unit of force. Using Newton's law, it is defined by the > force that is needed to accelerate one kilogram of mass from zero to the > speed of one meter per second during one second (1 m / s / s) and as > such independent of local gravity. Using the average gravity constant of > our planet, it turns out that one Newton is approx. 1/10 of a kilopond > or kilogrammforce (exactly 1 N = 1 / 9.81 kp = 0.102 kp). Newton himself > never explained the difference between heavy mass and inertia of mass. > > For engineering purposes, and to maintain the same figures and values > they were used to, the old mechanical engineers used metric prefixes and > made up the DekaNewton = ten Newtons, abreviated DN (greek: deka = ten, > abbrev. D ). One DekaNewton = 1.02 kp, so, for the time being, they > could keep using those old handbooks and their figures of material > properties. It was, though, easy to confuse with the abbreviation for > "nominal diameter", DN, so this was not successful on the long run. > > To express angular momentum, we have to multiply force by the length of > the lever, i.e. one meter. So we arrive at the unit DNm = 10 Nm ^= 1 > kpm, and the world is in almost perfect order again. > > So far, this was all based on the kilogramm-meter-second system (KMS). > In physics, they used another widely used system which gave handier > figures for small scale considerations, the gramm - centimeter - second > system (CGS). In this system, the unit of force is one dyn = 1 gramm > divided by 1 cm / s / s. 1 N = 100 000 dyn, 1 Nm = 100 000 dyn m, 1 dyn > = 1/100 000 N. The world was a hundred thousand times smaller. > > So, to make a long story short, I think your unit of kdm could mean a > thousand dyn times meter, extremely unusual in technology and > engineering science: > 1 kdm = 1000 x 1/100 000 Nm = 1/100 Nm. Easy to confuse this dyn unit > with dezi- = 1/10! > > Now, your dad must have a pretty old car since this cgs system was > abandoned in 1978. Are you sure that the above explanation is right, or > is it rather the kiloDekaNewtonMeter? What is the value on that rating > plate? > > Best regards from > > Peter Blodow > > > > andy pugh schrieb: > >> On 16 June 2012 00:37, N. Christopher Perry<n_christopher_pe...@me.com> >> wrote: >> >> >>> There are about 1.3 Nm to a ft-lb. >>> >>> >> Which would reduce confusion no end, except motor manufacturers want >> bigger numbers, so like to use oz-inch in the US. >> >> There was a similar tendency in the metric world, but it seems to have >> passed. You do occasionally see motors with peculiar units, my dad has >> one with (I think) kilo-dyne-metres on the rating plate. >> (that's about 100 x Nm, ie 1 kdm = 0.01Nm) >> >> >> > > ------------------------------------------------------------------------------ > Live Security Virtual Conference > Exclusive live event will cover all the ways today's security and > threat landscape has changed and how IT managers can respond. Discussions > will include endpoint security, mobile security and the latest in malware > threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > > ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
