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Re: [Phys-l] backwards units : entrenched usage



On 05/17/2008 06:43 PM, Trevor Fink wrote:

I would like to offer 1 final thought. Why is it that, if we understand
what a calorie is, we can't say that substance has 1,000 calories?

You can say whatever you want ... the only question is, will it
be clearly understood? In the context of a food label, you can
probably get away with saying "1000 calories". But more generally,
you need to say /what was measured/ -- not just what is the unit of
measurement.
*) 1000 calories of heat in a hot chunk of iron (in the context
of a heat capacity experiment)
*) 1000 calories of food value
*) 1000 calories of fuel value, in the form of gasoline, even
though it is indigestible and has no food value.
*) et cetera.

Never confuse the thing being measured with the unit used to measure
it. Knowing the unit does not generally tell you what's being measured,
nor vice versa.

... I do not understand why "the RPMs are"
is incorrect. I would conclude that onset to read, "The RPMs are equal to
1,000." This, to me, means the same as, "The engine is operating at 1,000
RPMs."

Those two interpretations are diametrically inconsistent as to
the algebraic status of what an "RPM" is. If you try to use both
interpretations, you will soon run into all sorts of inconsistencies.
So you have to choose. The "1000 RPM" interpretation is very strongly
preferred, because it is consistent with attributing physical reality
to the RPM unit, as discussed in much greater detail (with diagrams
and equations) at
http://www.av8n.com/physics/units.htm

In any case, never confuse the thing being measured with the unit
used to measure it.



When did we decide that apostrophes were optional?

What do you mean by "we", Kemosabe?

I do not consider punctuation optional.

People use punctuation because it is meaningful.

A panda walks into a bar. He orders a sandwich, eats it, then draws a gun
and fires two shots in the air.

"Hey, what are you doing? Where are you going?" asks the confused waiter,
as the panda walks towards the exit. The panda produces a badly punctuated
wildlife manual and tosses it over his shoulder.

"I'm a panda," he says. "Look it up."

The waiter turns to the relevant entry and, sure enough, finds an explanation.

"Panda. Large black-and-white bear-like mammal, native to China.
Eats, shoots and leaves."