I agree we need "kind". (01)
Just because two quantities have the same units doesn't make them
indistinguishable. You cannot look to the units alone. (02)
I believe that angle and count are distinguishable by their ostensive
definitions: they are not measured by the same procedure. (03)
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 distinguished.
(We can never know if they can never be distinguished). (04)
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". (05)
jbc (06)
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/VIM):
> "Add more until you can tell the difference between energy and torque."
> (or, equivalently "the diff. between an angle and a count")
>
> ...which brings us back to "kind of quantity", something of which I thought
> would've been accepted for quite some time already. I'm confused ...
>
> Regards,
>
> -Martin
>
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Joseph B. Collins, Ph.D.
Code 5583, Adv. Info. Tech.
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