On Sep 25, 2009, at 3:45 PM, Joe Collins wrote: (01)
> I agree we need "kind".
> Just because two quantities have the same units doesn't make them
> indistinguishable. You cannot look to the units alone.
> I believe that angle and count are distinguishable by their ostensive
> definitions: they are not measured by the same procedure. (02)
Um... as I recall from the telecon presentation, UCUM treats angle as
a physical dimension, so this entire debate is beside the point. There
is a *unit* distinction between angle and count; angle is not
dimensionless in UCUM. Very sensible move. (03)
Pat Hayes (04)
> The "kind" concept as a defined abstraction may seem a little
> arbitrary, but it
> usually follows from the ostensive definitions. If not, it should
> follow from
> known laws of physics whether two things are of the same kind.
> Things of the same kind can be meaningfully compared (>, <, =,
> etc.), which
> usually means they show up in the same law of physics or a set of
> measurements/experiments shows the kinds cannot (yet) be
> (We can never know if they can never be distinguished).
> Sometimes things are not considered to be the same kinds of quantity
> and are
> later determined to be of the same kind. Mass shows up in these
> three apparently
> distinct laws: F=m*a, |Fg|=G*m1*m1/(|r*r|), E=m*c*c. From the
> classical view
> these describe three unrelated classes of phenomena. Is it the same
> kind of mass
> in each case? Physical theory says "yes".
> Martin S. Weber wrote:
>> Joe Collins wrote:
>>> My question is, "Do we need more than this?".
>> My answer on that one is (which I believe to be consistent with SI/
>> "Add more until you can tell the difference between energy and
>> (or, equivalently "the diff. between an angle and a count")
>> ...which brings us back to "kind of quantity", something of which I
>> would've been accepted for quite some time already. I'm confused ...
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