On Sun, 18 Jun 2006 07:10:56 -0500, "gravity"
wrote:


Given the looseness of use of the unit lb to specify mass and
(incorrectly) force, it is a bit ambiguous... but he probably means
mass.

lbs is always force as far as i know. slugs is mass.

so long as we are confined to the planet earth, there is no difference
really. 1 kg (mass) always weighs 2.2 lbs (force). obviously if you go to
the moon ...

kilogram, slug -- mass
newton, pound -- force


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.

Practice may be different in different places, but I suspect that it
is laxness on the part of practitioners who refer to force in units of
pounds.

I just had a look at Wikipedia (which isn't the oracle), here is their
summary:

"The pound is the name of a number of units of mass, all in the range
of 300 to 600 grams. Most commonly, it refers to the avoirdupois pound
(exactly 453.59237 g), divided into 16 avoirdupois ounces. There is
also a unit of force corresponding to the avoirdupois pound, see
pound-force."

Wikpedia highlights just another aspect of the unit, its flexibility!

Owen
PS: a slug is a unit of mass, and equivalent to about 14.6Kg or
32.2lbs. I don't think it is in wide use!
--