Join Date: Jan 2007
Location: Sacramento, CA USA 96814
As a side note, the secondary English unit of mass is the pound-mass (lbm), which, by definition is 1 slug/32.2. This is so one lbm will numerically approximately equal one pound-force (lbf, primary weight unit) when placed on a scale. And in fact, most balance scales that display pounds actually are calibrated in lbm, which is a mass. (Since the actual acceleration due to gravity is 31.some odd and variable number feet/sec/sec, 1 lbm doesn't exactly weigh 1 lbf. The difference is less than the accuracy of a normal balance or scale so we don't worry about it.)
Also, and this really screws with people when doing complex thermodynamic calculations between the units, but in the metric system, mass (grams) is a base unit, and weight (newtons) is a derived unit, calculated from mass. In the English system, it's opposite - weight (lbf) is a base unit, and mass (the slug) is a derived unit. A slug, by definition, is the mass that will incur a force of 1 lbf when subjected to an acceleration of 1 ft/sec/sec. Likewise, a Newton is the force incurred when 1 kg is subjected to an acceleration of 1 m/sec/sec. Note that neither system uses gravity in the definition of either force or mass.
(EDIT: I think I received payback)