What is the Different between pound-mass and pound-force?

Answer 1

"The difference is that a "kilogram of mass" is correct, whereas a "kilogram of force" is wrong.

"Kilogram" is a unit of mass. It's not a unit of force, and it's incorrect to say that something "weighs"

some number of kilograms."

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The first contributor returns, and reacts:

Although this window is not the place for debate, and the 'discussion' section is

provided for that purpose, I'm putting my reaction here, not only because the

second contributor decided to gently introduce his contribution with the gentle

announcement "The above person is wrong.", but because this topic is probably

the most consistently misunderstood one in the "Physics" category.

The second contributor puts himself in the awkward position of insisting that

1 kilogram mass weighs one kilogram on earth, but the same kilogram weighs

only 0.16 kilogram on the moon. He waves his hands in the air so vigorously

in support of his position that he runs the risk of breaking his arm. He is incorrect,

but he is more to be pitied than scorned. He is the natural result of an upbringing

in the American "customary" system, wherein the ratio among length units can be

3, 12, 36, 1760, or 5280, the ratio among volume units can be 8, 16, 32, 128, 231,

or 1728, an ounce can be either a force or a volume, and the distinction between

a poundmass and a poundforce is known to few outside of the laboratory.

The American 'customary' system is the main source of the customary American

ignorance of the specifics and confusion on the subject in general.

The 'kilogram' is widely and conveniently used as a unit of force equal to the

weight on earth of a kilogram of mass, but the convenience must not be carried

too far. It falls apart completely when anyone tries to allege formally that a

kilogram is a unit of force. It is not. Search "kilogram force" online, and one

discovers that it's described as an "informal unit". When the question is asked

by an individual obviously unclear on the concept, the easiest way to confuse

him forever is to include an informal unit in the initial response. He has to be

comfortable with the strictest formal units first, because they're the easiest to

understand. Telling him that the kg is both a mass and a force throws him back

down into the pot of inches, ounces, and acres, where the distinction between

force and mass is as relevant as alchemy and evolution, where innumeracy rules,

and a TV anchor who accidentally reveals that she understands a science story

has to apologize for it in the next breath.

Answer 2

Local accelleration or gravitation creates force. Mass remains constant despite presence or absence of accelleration or gravity.