[masraum]

Originally Posted by jyl

"lb" is not a unit of force .....
"lb" is a unit of mass. Force is mass x acceleration ( F = m *a ) and the unit of force is "lb * ft / sec^2". When we use "pounds" as a shorthand expression for force, we are implicitly leaving out the relevant acceleration..

Actually, you're both correct.

a slug is the Imperial unit of mass.

The slug is a unit of mass associated with Imperial units. It is a mass that accelerates by 1 ft/sec2 when a force of one pound-force (lbf) is exerted on it. Therefore a slug has a mass of 32.17405 pound-mass or

Also, in certain cases there is "Pound-mass" lbm and "Pound-force" lbf.

A pound-force is the amount of force required to accelerate a slug at a rate of 1 ft/s2