At the very bottom, please double-check your joule example. Taking a cup of coffee as about 150 mL or 150 g, and specific heat of water as 4.2 J/(g·K), I get around 630 J, not 1 J, from 1 K of cooling. (that's using the coffee institute's official coffee cup, mine is about 400 mL).
NOTE: A 238 mL cup would make a kilojoule, but that would mess up the apple example of mechanical work. ________________________________ From: Stanislav Jakuba <[email protected]> To: [email protected] Cc: U.S. Metric Association <[email protected]> Sent: Mon, July 25, 2011 7:54:15 PM Subject: Re: [USMA:50797] Re: MPGe = miles per gallon equivalent? Perhaps it will help newcomers to read the attached article published some 20 years ago and appearing on this forum periodically. Stan J. On Thu, Jun 30, 2011 at 10:12 PM, John M. Steele <[email protected]> wrote: Kilojoules are the appropriate unit for individual food items. A total human dietary requirement per day is around 10 000 kJ, which may be better expressed as 10 MJ. > >More relevant to a car is comparison to a horse pulling a carriage. A working >horse can only work part of day, and may have a daily requirement of 138 MJ >(33000 kcal, per Google) and travel 30 km, thus requiring 4.6 MJ/km or 4600 >kJ/km. A larger carriage might require a team of 2 or 4 horses having such a >requirement. > > > >--- On Tue, 6/28/11, Pat Naughtin <[email protected]> wrote: > > >>From: Pat Naughtin <[email protected]> >>Subject: [USMA:50775] Re: MPGe = miles per gallon equivalent? >> >>To: "U.S. Metric Association" <[email protected]> >>Cc: "U.S. Metric Association" <[email protected]> >>Date: Tuesday, June 28, 2011, 9:11 PM >> >> >> >>On 2011/06/26, at 22:36 , John M. Steele wrote: >> >>However, the numbers are getting small, and the 100 factor departs from the >>usual steps of 1000-fold in units. I believe it would be better to multiply >>by >>10 and use megajoules per 1000 kilometers (which could be expressed as a >>megameter). Alternatively the megas could divide out leaving joules per >>meter, >>certainly better in computation, but another representation might be more >>relatable to the public, and easier to tie to meaningful driving distances >>and >>volumes or masses of fuel. I would note that 1000 km is a reasonable monthly >>driving distance for many people, and the cost per 1000 km would be a >>reasonable >>budgetary visualization. >> >>Dear John, >> >> >>I think that I would prefer kilojoules per kilometre as cars already have the >>odometer in kilometres. In addition, the kilojoules is gradually becoming >>used >>as the correct energy unit for food energy values. Perhaps kilojoule is more >>common here but it is finally replacing calories. >> >> >>As the joule is the single unit for energy in the International System of >>Units >>(SI) it means that the energy used in a car can be compared with all other >>sources of energy that are reported in joules. >> >> >>Cheers, >> >> >>Pat Naughtin LCAMS >>Author of the ebook, Metrication Leaders Guide, see >>http://metricationmatters.com/MetricationLeadersGuideInfo.html >>Hear Pat speak at: http://www.youtube.com/watch?v=_lshRAPvPZY >>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 for many different trades, crafts, and professions for >>commercial, industrial and government metrication leaders in Asia, Europe, >>and >>in the USA. Pat's clients include the Australian Government, Google, NASA, >>NIST, >>and the metric associations of Canada, the UK, and the USA. >>See http://www.metricationmatters.com/for more metrication information, >>contact >>Pat at [email protected] or to get the free 'Metrication >>matters' newsletter go to: http://www.metricationmatters.com/newsletter to >>subscribe. >>
