Dear Robert,
In my view you are correct in that "quantity" implies "amount", but that
is precisely what is meant here and elsewhere. We are speaking of things
that can be measured; that is, they have "amounts" whether generally or
specifically known. And those amounts (quantities) can be related by
laws of physics and chemistry by means of mathematical formulae.
Consider the electrical current flowing through a circuit. We call that
quantity "electrical current" and often we wish to know the value for
that amount of electrical current. That amount is then the quantity
value. Sometimes we do not care to know the particular value for that
quantity but it is still useful to speak of it generally. Thus, in Ohm's
law, we do not speak of "25 amperes" but we speak of "electrical
current". That current might have differing values in differing instances.
To me, "property" differs from "quantity". Property describes an
attribute such as whether a substance is fluid or solid, diamagnetic or
paramagnetic, transparent or opaque, toxic or benign, lustrous or dull,
etc. Yes, for many properties, such as these, there are indeed
quantities that -- ahem -- quantify the extent of those properties. But
that is not always the case. Consider the property of visual appeal.
Only poets, painters, and sculptors can "quantify" beauty or ugly but
those valuations are not universally repeatable.
Jim
On 2014-01-06 10:35, Robert H. Bushnell wrote:
2014 Jan 6
Dear Barry,
Thanks for posting the web address for the draft 9th SI.
I have long been concerned about the use of the word
quantity in SI. To me quantity means amount. I think the public
also thinks quantity means amount, that is, how much. In the
draft, including the history part, I find no text saying why
this word quantity is used. So, who can tell me?
I propose that quantity be deleted and the word property
be used instead. There might be another English word to use.
Somebody tell me what to use.
Property is what units are about.
"Property" is used throughout the text so this change is
not easy but let's do it. We have confused the public too long.
Robert H. Bushnell PhD PE
member USMA
[email protected]
502 Ord Drive
Boulder. CO 80303-4732
303-554-0728
