daestrom wrote:

"krw" wrote in message
t...
In article ,
says...
In article ,
krw wrote:
In article 39,
says...
NameNotImportant wrote in
m:

lbm?

I'm not sure on your units.

pounds (mass), lbm, as opposed to pounds (force), lbf, or lb.

It is necessary to distinguish between mass and force but they
are both
measured in pounds in the english system.

The "English" system uses the "stone" as the measurement of mass.
The pound ('lb') is the unit of *FORCE*.

The 'Stone' is a unit of mass, not "The unit of mass"

It is *the* unit of mass. The pound-mass is a recent abortion.


If you call the past 100 years or so, 'recent'. I myself have
text-books from the '50's that use this 'recent abortion' as you call it.

Considering the separation of force and mass was first worked out
*after* the original 'pound' for weight was in common use, it was
necessary to separate which 'kind' of 'pound' was being talked about.
The one that represents how much *force* is being applied to something,
or the one that describes how much resistance to acceleration something
has.

But for a long time a 'pound' of something was a certain amount of mass
-or- the force applied to a surface by placing that certain amount of
mass on it (such as used in 'dead-weight' testers for pressure
instruments).

In a few obscure bits of engineering, you can even find the term
'kilograms of force' used. Obviously that is the force applied by
placing a kilogram of mass on top of something. You can even find some
pressure gauges calibrated to read 'kg/cm^2'. Proof that you can mess
up things even with the metric system. ;-)

I'm not sure how old the 'stone' is, but I suspect it too was around
before we knew the difference between force and mass. Stone is common
in UK still, but it never caught on in the colonies, even as far back as
colonial days when 'hundredweight' and 'long ton' were in common usage.

Trouble with pound-mass (lbm) and pound-force (lbf) is that to make F=MA
work out, you need to keep another 'conversion factor', the dreaded
g-sub-c (g-sub-c = 32.2 lbm-ft / lbf-s^2), around and figure out when to
throw that into the mix.

An excellent compilation of measurement units, may be found he

http://www.unc.edu/~rowlett/units/index.html

Note that mass, (kilogram), is the only fundamental unit that is not
defined by a property of nature.

--
Virg Wall, P.E.