Stan,
I appreciate your point that citing some number of joules used in a year
is a rate of energy usage, which falls in the category of power or
energy rate.
But I think that one needs to be flexible and sensitive to rhetoric and
context. If an author compares the energy consumed in various forms in a
year's time, then most certainly the author is comparing amounts of
energy and that should be measured in joules. As long as all categories
cover the same time period the comparison is fair.
Some of those forms of usage might be rather sporadic, such as the
consumption of stove wood. I use stove wood in the cold months here. So
I endeavor to enter that cold period with a certain quantity of wood,
which I roughly measure by volume. It contains a certain amount of
useful energy -- depending on that volume, the wood's moisture content,
and the types of trees that it came from. As I am accumulating that
supply of stove wood, I don't give a single thought to its rate of usage
and therefore not to its output energy rate. I want to have some minimum
amount of heat available, regardless of its rate of usage.
So I have no heartburn with folks who would like to cite values for the
amount of energy produced by each source of that energy in a set period
of time and using the joule as the unit of measurement. I'm certainly
smart enough to divide by the number of seconds in that period of time
to view this usage in terms of rate of energy production, measured in watts.
Of course, one could make that comparison in watts, as you prefer, and
then multiplying by the number of seconds in that period to obtain the
total amounts of energy produced in that period by each source.
Presenting such data in watts invites easy comparison to other
"benchmark" figures people recall, such as the power rating of their
nearest power plant. Again, let the rhetoric and the context provide the
guidance.
The beauty of the SI is that it lets readers quickly make such
calculations. It's our collection of U.S. Customary units that makes
such calculations difficult. If we were stuck with those units, then it
would be worth arguing about which presentation is preferable before
going to the bother of publishing a comparison. But since we have the SI
available, citing either annual energy production or the rate of energy
production is sufficient and understandable. This dispute reminds me of
arguments about the direction in which those angels dancing on the head
of a pin are circling. Clockwise or counterclockwise? Hmm ... as viewed
from above or below?
The same can be said for claiming (incorrectly) that the SI prefers the
joule over the watt second. Neither is preferred. Specially named units
are for convenience and are not mandated. If you disagree with me on
this, Stan, cite the clause in the SI brochure that contradicts me.
Let's not discourage any budding metric fans here by bogging down into
arguments of relative purity, especially those that are not
substantiated by the standards.
Jim
On 2014-12-17 09:10, Stanislav Jakuba wrote:
In due respect, Gene, there is no need for the alternative W.s as
there is no need for the N.m (for work) or the kg.m2/s2. Associating
any quantity with only one form of its unit represents a major
advantage of SI. Let's stick with it. The joule is the only form for
the unit of energy to be used in practice.
To those who commented on this email, and I thank you all, you should
know that the Editor "bought" the reasoning and plans the article for
the January issue.
Stan Jakuba
PS: While on this topic, the above principle applies also to the
quantity "energy consumption" that is universally expressed, wrongly,
as Btu/day, MWh/year, etc. In the spirit of SI, the ONLY unit for
power is the W. And because energy consumption is a flow, the unit of
power (W) is correct here despite the almost universal, worldwide
opposition. Imagine that "... per day, per year, per hour, per minute,
per decade ..." all gone with the watt. Suddenly all statistics are
comparable directly.
On Mon, Dec 15, 2014 at 11:58 AM, mechtly, eugene a
<mech...@illinois.edu <mailto:mech...@illinois.edu>> wrote:
Stan,
The “joule” of energy equals exactly one “watt.second”; the
product of the watt and the second, where all reasonably literate
persons have heard of the watt and the second,
and might even know that the watt of power is *defined* as one
joule per second for the time rate of energy processing or transfer.
Try using the watt.second (Ws or W.s) in your writings, until your
readers are more familiar with the joule.
Gene Mechtly.
On Dec 15, 2014, at 8:17 AM, Stanislav Jakuba <jakub...@gmail.com
<mailto:jakub...@gmail.com>> wrote:
*USMA members will, I hope, be pleased reading the answer to an
editor who desired that American units be presented alongside the
SI values in my manuscript. *
*
*
*Dear ....*
*I attempted the parenthesis you suggested but found the
resulting complexity of the text disruptive and harder to read.
And there are other problems associated with doubling each unit.
Allow me a few words of explanation.*
**
*The article is about comparing two sets of numbers. For that,
there need not be any unit at all. The majority of readers will
skip the units anyway, and the few curious engineers and physics
teachers will know how to convert to whatever units they like. As
to the several common values I doubt that there are readers that
wouldn't know that water freezes at 0 deg. Celsius or what a km
is. As to the substitution for the one still unfamiliar unit –
the joule or MJ – here Americans use several different units for
energy such as calorie, Btu, kilowatt hour, lb-ft. As a result. I
am at a loss which one to select. Different professions** use
them all – that would be four parentheses. Instead, I spelled out
the symbol MJ and use it consistently thereafter. Thus no problem
with comparing numbers. In any case non-technical readers will
not care, and experts who might be checking the math will convert
the value to whichever unit they like. I am pleased to say that,
up to now, **no publisher asked me to add conversions. Dozens of
articles, no complains. May I say that one might underestimate
one’s readers?*
**
*As a side issue, you may be interested in why I insist on the
units of a system that has only one unit for any measurement, be
it energy, power, or length. That’s because, with the
multiplicity of the U.S. energy and power units, it is common to
present false or misleading numbers and get away with it for it
is too difficult and bothersome for readers to look up all the
conversion factors to check. I might also point out that since it
is the Federal Law and Exec. Order that state that "SI metric is
the preferred measurement system in the **U.S.**" my writing in
SI only should help citizens learning it. Once they see how
**easy comparisons are with SI units, they might actually prefer
that system particularly when noticing the cheating in the daily
press with American units such as the one illustrated in the
other enclosed treatise. *
*Yours,*
*Stan Jakuba*
**
