Hello All!

A college student I know was recently asking me a question about nomenclature that I was not sure I could clearly answer.  I am hoping that you can provide me some guidance and a more logical explanation to provide him.  

What is the difference between a lbm and a slug and how do each of these translate into lbf?

My thought was that lbm=slug and both when multiplied by gravity/acceleration provide force.  Is this correct, or have I further misguided an already confused college student?

Reprinted from,

Ed Gohmann
Purdue University School of Technology
New Albany, Indiana


In the meter-kilogram mass-second system it is defined that one Newton (N) of force will accelerate 1 kilogram mass (kgm) 1 meter per second squared. Thus for the mkgs system

1/K = 1 N*sec2/kgm/m

or practically

F (N) = m a kgm*m/sec2

A parallel is found in the English system which defines that 1 pound force (lbf) accelerates 1 slug mass 1 ft/s2 resulting in

1/K = 1 lb(force)*sec2/slug/ft

or

F(lbf) = ma  slug*ft/sec2

Quite often in this system mass is given in pounds mass (lbm) with the fact that one slug equals 32.17 lbm. Thus to obtain slugs when given lbm you divide by 32.17 lbm/slug.

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