On 9 Dec 2003 10:34:34 -0800, (Fred the Red
Shirt) wrote:

Russell Kent wrote in message ...


I'm sorry, you're correct. I didn't mean to imply that they are the only unit of
mass. I was taught (perhaps incorrectly) that the unambiguous term for weight
(scientific meaning) in the English system was "slugs". Apparently it's also
"pounds force" now (it may have been them, too, and I've just forgotten it).

I think you mistyped. 'Slugs' are unambiguously a unit of mass.

Pounds are ambiguously a unit of force. Ambiguity exists because it
is popular in some disciplines to use a unit of mass defined (loosely)
as that mass which weighs one pound.

But you knew that.

Well, now, in this fuzzy dreamworld you inhabit, what exactly is the
standard for a pound?

What is the nature of this standard? Something electrical, something
mechanical, or what?

Who made it the standard? When exactly was it made the standard (just
the year will do)?

Where is the standard kept, and who maintains it?

Now for the bonus question:

In addition to the system in which slugs are the units of mass, there
is another, much older English foot-pound-second system in which the
poundal is the derived unit of force. It is the force which will
accelerate the base unit of mass in this oldest English subsystem of
coherent mechanical units at a rate of 1 ft/s². Now, fill in the
blank, please: The base unit of mass in this oldest fps system is the
_____________. (Hint: it is the "p" in this fps system.)

When the poundal system was invented back around 1879, not only did
slugs not exist but also pounds force had never been well-defined
units. This was before anybody ever started picking some "standard
acceleration of gravity" which is an essential ingredient in the
definition of those pounds force. Even today, pounds force don't have
an official definition, at least in the United States. We often
borrow the value for the standard acceleration of gravity which is
official (adopted by the CGPM in 1901, long after the poundal system
was in use and the dyne system in cgs units) for the purpose of
defining kilograms force, i.e. 9.80665 m/s². But other values are
also used for this purpose, such as 32.16 ft/s² (you still commonly
see this used in ballistics with a formula for kinetic energy in a
foot-grain-pound force-second system E = m v²/450240).

--
Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/
"It's not the things you don't know
what gets you into trouble.

"It's the things you do know
that just ain't so."
Will Rogers