No, Gene, I absolutely don't mean devices with springs. I mean the type of device I used to use in the physics lab in high school, with the box of weights and the tweezers for handling them (to avoid modifying their mass by the deposition of sweat). So I'm talking about achieving equilibrium by placing the appropriate standard masses on one scale pan to ascertain the mass of the object on the other scale pan. No springs, Gene. None whatsoever. I've always understood "balance scale" to mean just that -- balance. Bill Potts, CMS Roseville, CA http://metric1.org [SI Navigator] > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On > Behalf Of Gene Mechtly > Sent: July 10, 2001 16:20 > To: U.S. Metric Association > Cc: U.S. Metric Association > Subject: [USMA:14289] Re: Constitutionality > > > On Sun, 8 Jul 2001, Bill Potts wrote: > > ... > > The only scales that measure mass are balance scales, ... > > Yes, Bill, but only if by "balance scales" you mean "devices which bring > forces into static equilibrium" including springs. > > You give me a set of standard masses and a spring (or any of many other > elastic devices, e.g. load cells) which acts as F = - k d, where F is > the restoring force, d is the displacement (elongation or compression), > and k is the elastic constant of the device in newtons per meter and I'll > calibrate the device to measure mass at the location of calibration. > > > ... > > However, given that they are calibrated on the Earth and in the general > > geographic area where they are to be used (i.e., given the > constancy of the > > ratio of measured force to actual mass), the units displayed > can reliably > > indicate the mass placed on them. > > That is the point, Bill, *calibration* of elastic devices in units of mass > at a particular location. e.g. the load cells at your grocery store. > > Gene. >
