On 2007 Apr 26 , at 3:31 PM, <[EMAIL PROTECTED]> wrote (quoting me):
One pound of mass is defined as the mass whose
weight force is 1 pound of force.
False.
One pound of mass is *defined* as 0.453 592 233 7 kilogram,
exactly, *independent* of gravity. (i.e."avoirdupois" pound)
Yes, Gene is correct.
I should not have used the word "defined". I was trying to suggest
how the concept of a "pound-mass" could be explained to someone who
was familiar with the pound as a unit of weight (the pound-force).
I should have said that:
"One pound of mass IS EQUAL TO that mass which has a weight of one
pound-force."
It is true (I believe) that the pound of force is defined as the
weight of a pound mass (and the pound mass is defined in terms of the
kilogram of mass as, Gene said). I just turned this definition
around, in an effort to make it match the way I was describing other
relationships in my message. Turning it around might have been OK for
an equivalence but it is incorrect for a definition.
Thus, it is possible to refer to the EQUIVALENCE of "pound-mass" and
"the mass of something that has a weight of one pound-force" either
way (if A=B, then B=A; it's equal either way). However, it is not
correct to reverse the order of a definition since such definitions
indicates which is more fundamental and which other thing is defined
in terms of the more fundamental one. Reversing a definition
constitutes and error in understanding which one is based on which.
Thanks to Gene for catching my slip-up and correcting it.
Regards,
Bill Hooper
Fernandina Beach, Florida, USA
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SImplification Begins With SI.
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