Conveniently, an energy cost in kJ/km is numerically equal to that
energy cost in J/m. In fact, they ARE identical algebraically. Thus one
can quote a figure in kJ/km to the public while using that same number
in calculations in the lab or design shop. This is convenient when
databases or spreadsheets are used, since the units are normally carried
in separate fields or cells.
Wind speeds are a different matter, of course. A wind speed in km/h is
NOT numerically equal to that wind speed in m/s. One must take care lest
a Martin-Lockheed event occur (mixing numbers with incorrect units).
Jim
STANLEY DOORE wrote:
Pat et al.
Yes Pat, J/m is cleaner and consistent with the SI; however, people
don't relate very well to meters when traveling without having to make
a conversion. We found years ago that the Soviet Union used m/s in
reporting wind speed instead of knots in reporting their weather
observations. That didn't go over very well.
However, we used m/s in our numerical analysis and forecast models
(and still do) for computational reasons by converting whatever the
countries, including the US, reported for wind speed to m/s as
our standard. We made the conversion even for the US observation
reporting system from miles per hour and/or knots to m/s too since the
US used both. In the 1970s I tried to get all US agencies to take
observations in m/s but that didn't go over very well, including
readouts for new automatic wind speed devices. I don't know what the
NOAA, DoD and other US agencies observation standards are today. I
think the FAA still uses knots.
Regards, Stan Doore
----- Original Message -----
*From:* Pat Naughtin <mailto:[EMAIL PROTECTED]>
*To:* U.S. Metric Association <mailto:[email protected]>
*Cc:* USMA Metric Association <mailto:[email protected]>
*Sent:* Saturday, July 12, 2008 7:41 PM
*Subject:* [USMA:41403] Re: Newton for automobile efficiency
On 2008/07/12, at 7:46 PM, STANLEY DOORE wrote:
This discussion about how to present a standard way of
efficiency has two components - technical and useful for public.
the discussion so far have evolved around the technical/scientific
and not the practical use.
The bottom line is the pocketbook - what's the best way to
minimize cost to the user.
*xJ/km* seems to fulfill this best since it relates to every
day life for vehicles. Then prices can be posted in a standard
xJ/km so people can directly compare costs. In effect that's what
the designations of regular, high test (hi-energy), diesel grade
fuels do for customers, and they give you, indirectly, a bottom
line dollar or Euro cost for efficiency to get you from one place
to another.
*xJ/km* then could also be used as a common denominator for
the cost of moving people or freight by rail, bus, car, air, ship,
etc. which people would understand.
Stan Doore
Dear Stan and All,
Using the figures
from http://www.bwl.admin.ch/themen/00509/00528/index.html?lang=en
it follows that walking at a comfortable speed of 4 kilometres per
hour would require using energy at a rate of 150 kilojoules per
kilometre.
I think that I would be more comfortable if this was expressed as
150 joules per metre. This would meet a number of conditions:
1 It would comply with the ISO SI Guide (English Edition 2 2008)
rule (page 10) that:
/Prefixes in the denominator should preferably be avoided./
2 It also uses the ISO SI Guide rule (page 10) that
/The prefix /(for the numerator)/ should generally be chosen so that
the numerical value will be between 0,1 and 1000, …'/
3 Far less importantly, it complies with my suggestion that you can
make calculations easier, and communication much better, if you
choose SI prefixes and units so that the range of values likely to
be used with that prefix/unit combination will fall into the range
of whole numbers without common or vulgar fractions
and without decimals
(See: http://www.metricationmatters.com/docs/WholeNumberRule.pdf ).
Some other approximate values (to compare with walking) are:
Cycling 80 joules per metre
Walking 150 joules per metre
Jogging 270 joules per metre
But note that some human activities take much more energy
Swimming 60 000 joules per metre
For motor transport (numerical factors
from http://bioenergy.ornl.gov/papers/misc/energy_conv.html )
Motor bike 150 joules per metre
Car 300 joules per metre
Truck 600 joules per metre
Cheers,
Pat Naughtin
PO Box 305 Belmont 3216,
Geelong, Australia
Phone: 61 3 5241 2008
Metric system consultant, writer, and speaker, Pat Naughtin, has
helped thousands of people and hundreds of companies upgrade to the
modern metric system smoothly, quickly, and so economically that
they now save thousands each year when buying, processing, or
selling for their businesses. Pat provides services and resources
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