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
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