Dear John and Ezra,
Two thoughts occur to me.
1 How wonderful is the metric system? Here is an obscure application —
getting the electrical energy form an off-shore wind energy source,
and in a matter of moments the engineers can derive an appropriate
unit, directly from the SI base units, that is coherent and the best
fit for this application.
2 Isn't it odd that the 'unit' for currency, dollar (symbol $), was
fitted to numbers at the front rather than at the back; we write two
dollars as $2 rather than as 2 $. In the application that Ezra found,
it would make more sense, to me at least, if it was written as 30 $/
kA·m with all symbols after the number.
Cheers,
Pat Naughtin
Geelong, Australia
On 2009/04/08, at 6:29 AM, John M. Steele wrote:
It is a kiloampere-meter.
It is an alternate way to express an amount of wire. To carry a
given current, a wire needs a certain cross-sectional area, but the
area depends on what the wire is made of.
A way to equalize and express costs across wire types is to rate by
current carried, for each wire type that will require a certain
area. Multiplied by the length of the wire, that gives volume and
should be proportional to cost (at least fairly proportional).
However, I don't think I've ever seen it before. I had to read the
conext in the article to see what it is about. It is a clever way
to relate the cost of the wire to its mission (carrying current for
a distance) rather than purely by dimensions.
It is analogous to looking at cost of fuels per unit of heat energy
rather than by volume or weight.
--- On Tue, 4/7/09, [email protected] <[email protected]
> wrote:
From: [email protected] <[email protected]>
Subject: [USMA:44462] Strange SI units
To: "U.S. Metric Association" <[email protected]>
Date: Tuesday, April 7, 2009, 3:46 PM
Just came across this article:
http://ptonline.aip.org/journals/doc/PHTOAD-ft/vol_62/iss_4/25_1.shtml
but was flummoxed by this part:
$30/kA·m
What the heck is kA·m and why do they use it?
Ezra
Pat Naughtin
PO Box 305 Belmont 3216,
Geelong, Australia
Phone: 61 3 5241 2008
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