Re: weight = mass or force?

In article <87zm8s2kz6.fsf@xxxxxxxxxxxxxxxxxxxx>, Phil Carmody <thefatphil_demunged@xxxxxxxxxxx> writes:
mmeron@xxxxxxxxxxxxxxxxxx writes:
In article <871wm45xao.fsf@xxxxxxxxxxxxxxxxxxxx>, Phil Carmody <thefatphil_demunged@xxxxxxxxxxx> writes:
"Greg Neill" <gneillREM@xxxxxxxxxxxxxx> writes:
Sorry, I meant to say that balance scale mechanisms
in themselves do not measure weight; they compare
masses.

Nonsense. Firstly, they only work in the presense of a
prevailing gravitational field, and even then when you
use them in the right orientation. Secondly, they compare
moments. And given the distance at which the force is
acting is usually constant, that means that they compare
forces.

While they rely on the presence of a gravitational field, the value of
said field is irrelevant (as long as it is not zero). Balance scale
mechanisms compare masses, period.

The way you use a balance compares masses because the torque is
known to be proportional to the force, and the force is known to
be proportional to the mass.

Yes. So? That measurements rely on prior knowledge or assumptions,
that's not new. All measurements do.

To say you've only been comparing masses is pure twaddle.

Since everything else factors out, that's exactly what you do. You're
comparing masses. A balance scale compares an unknown mass with a
known one and it'll read the same whether the local gravitational
acceleration is 1g, 10^(-6)g or 10^(6)g. If that alone doesn't tell
you that this is not a measurement of forces, then you don't know
enough about measurements to intelligently discuss them.

There is an old fashioned electrical resistance measurement technique
called Wheatstone bridge. I won't give you the details, you dshould
be able to find them yourself, but through the measurrement you
adjust a potentiometer till a current reading goes to zero.
Nevertheless, this is ***not*** a current measurement but, as I said,
a resistance measurement. The zero current condition simply allows
you to compare an unknown resistor with a known one. The balance
scale is the same thing.

A physical measurement is, in the ultimate account, the comparison of
the measured quantity with a standard quantity of same kind. Various
intermediaries can and usually are used in the process but what is
being measured is determined by the standard to which the comparison
is being made.

Mati Meron | "When you argue with a fool,
meron@xxxxxxxxxxxxxxxxx | chances are he is doing just the same"
.

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