Chris W wrote:
Owen Duffy wrote:


I was taught (in imperial units) to differentiate mass (pound) and
force (pound-force). That learning stood me well when we changed to SI
(metric) part way through school.


You were taught wrong. If you use pounds in a formula that wants mass
such as F=M*A you will get the wrong answer. So lets say you weigh 200
lbs on earth where A = 32 ft/sec^2. You can then calculate your mass by
solving for M = F/A or 200/32 = 6.25. . .

That's 6.25 pounds mass, I presume, for someone weighing 200 pounds force.

In my entire engineering school curriculum, I had only two courses which
didn't use the metric system, Statics and Dynamics, taught by the civil
engineering department. I have vague recollections of pounds force,
pounds mass, slugs, and poundals. As often as not, my answers were off
by g^2, since I never could remember which ones already had
gravitational acceleration built in and which didn't. But I developed a
method to deal with it. When presented with a problem, I first converted
everything to SI units. Then I solved the problem and converted the
answer back to U.S. units.

What a horrible system! My hat's off to the Canadians, who had the will
to convert, and established -- and stuck with -- a systematic program to
do it. What the U.S. did was to declare the metric system to be official
("Mission Accomplished!") and change whiskey bottles from fifths to 750
ml (which was promoted by the booze industry because it made the bottles
just a little smaller and they could charge the same price). Wow.

Roy Lewallen, W7EL