Re: So, I got my OW Cert

On Sun, 2 Jul 2006 18:34:10 -0400, "Lee Bell"
<pleebell2@xxxxxxxxxxxxx> wrote:

Furthermore, it doesn't matter what kind of device is used in commerce,
because the scales used in commerce are calibrated and tested in situ,
for the accurate measurement of mass in the location in which they are
used. In other words, any other scale, to be legal in commerce, needs
to give you results similar to what a balance would give you.

To put a fine point on it, no. The scales are calibrated to give a specific
weight which corresponds to a specific mass.

They are calibrated to give a measurement which does not depend on the
strength of the local gravitational field. They are calibrated to
give a measurement of mass. The force actually exerted by the contents
(or, for that matter, by the contents plus the container) isn't
measured.

Of course, when we are interested in force, the force exerted by the
container is just as important as and undistinguishable from the force
exerted by the contents.

Furthermore, the fact that the law defines a pound as a unit of mass
exactly equal to 0.45359237 kg is also relevant. That pound and that
kilogram, both units of mass, are the units required to appear on many
labels in the United States; in the rest of the world, the kilograms by
themselves are sufficient.

Not surprising, a pound of weight also equals 0.45359237 kg of weight.

Lee

Not necessarily.

We do have an official defintiion of pounds as units of mass, one that
is uniform worldwide since a 1959 agreement among the national
standards laboratories of the U.S., Canada, the U.K., South Africa,
Australia, and New Zealand. (Before 1959, there were some national
variations in the official definitions.)

But while we do now have a uniform, official definition of a pound,
that isn't the case with the pound force, as NIST admits in the
conversion factors in the appendix of SP811. The lawmakers, of
course, have primarily been concerned with the regulation of the usage
in commerce; they don't particularly interest themselves in what
someone might do in a scientific laboratory. But no international or
professional standards organization has bothered to define a
pound-force either.

Many people do borrow the acceleration which is official for defining
grams force for the purpose of defining pounds force as well--but
there is no particular reason why this has to happen. In that case,
pounds force will indeed bear the same relationship to kilograms force
as pounds do to kilograms.

However, some people do use an acceleration of 32.16 ft/s² to define a
pound force, for example. In that case, since the acceleration to
define a kilogram force was established in 1901 by the CGPM as 9.80665
m/s², using that 32.16 ft/s² will give you the following approximate
relationship:

1 lbf = 0.45339431 kgf

Gene Nygaard
Gene Nygaard
.

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