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
To: U.S. Metric Association
Cc: USMA Metric Association
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
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