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Electrical heat gain - Page 7

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Posted by Eeyore on April 17, 2009, 11:42 am

daestrom wrote:

Those aren't conversion factors. You're simply stating the same thing using
different dimensional units.

Dimensional analysis applies to every sytem of measures.


Posted by daestrom on April 18, 2009, 1:47 pm

Well, by your definition, then saying that 1 btu = 1055 Joule isn't a
conversion either.  It's just 'different dimensional units'.  After all,
both BTU and Joule are simply units of energy.

Exactly right.  And not carrying them through because all the 'conversion
factors' are just 1 means you run the risk of not getting the right result.
Just because the conversion factors in some systems of measure are 1.00 and
in others they are something else besides 1.00 doesn't make one system
superior to the other.

If anything, the one that always has unit conversions of 1.00 will lull you
into complacensy and screw up by forgetting (in your case even denying) that
you're doing unit conversions.


Posted by Jim Wilkins on April 18, 2009, 2:09 pm
Eliminating conversion factors was useful back in the era of
multiplying & dividing with slide rules and adding & subtracting
intermediate results on paper. We ran three parallel calculations; the
values, the exponents and the units, and sometimes an order-of-
magnitude sanity check as well. Calculators are sooo much easier but
also more likely to lead you astray.

Jim Wilkins
BS Chem 69

Posted by Eeyore on April 18, 2009, 3:54 pm

daestrom wrote:

Same dimensions, different measurement systems.

Well, I disagree and I've been there, and it seems you have not.

Realistically, the world isn't going to change back to old UK or US units. Thank
God for that too, although since I gew up with Imperial measures, I still use
feet and inches for everyday use ( and metres too ) , but any technical drawing
will be metric. I have no trouble with that.


Posted by Mike on April 17, 2009, 3:52 pm

We use Newtons, not kg

The Europeans might, the Brits (general public when inflating tyres)
commonly use psi or occasionally bar ( = 100 kPa)   Real world
engineering uses psi, bar, Pa depending on which way the wind is
blowing and the specific application.

Many years ago I heard an Australian weather forecast that used Hecto
Pascals this was the first time I had ever seen the hecto multiplier
in use (with the exception of hectares!) after 20 years of using SI
units and I vaguely recalled the first day I saw a list of SI
multipliers.   I knew the numbers (circa 1000) they quoted were in the
same region as those for millibars, but until I sat down and really
thought about it I was totally convinced that by using Hecto Pascals
they were out by a factor of 10.

Substitute 1 kg, 1 deg K, 1 Joule, 1 Newton as necessary

It's ok I do know about metric water :)


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