The point below is an important one. Measuring in seconds is obviously superior for many scientific and technical purposes, but in everyday life we often use hours. If I use a 100-watt light bulb for 10 hours, it uses 1 kWh of electric energy. This is equal to 3.6 MJ, but you lose the round numbers. For the average consumer, it is probably more informative to get electric bills in kWh. Automobile speedometers give values in km/h because those units are more useful when you want to know how long it will take to get to your destination. You would measure a car ride as twenty minutes, not as 1200 s. It's also more convenient to use degrees Celsius in everyday life rather than kelvins. Each of these units can be converted to pure SI units without much effort, but they are more convenient.
Carl Sorenson -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Joseph B. Reid Sent: Saturday, July 13, 2002 7:49 PM To: U.S. Metric Association Subject: [USMA:21058] Re: No Nonsense If I understand Gene aright, he would ask that automobile speedometers be graduated in metres per second rather than km/h. He wrote me on 2002-07-13 at 13:53 >Joe, > >In defense of Bob Bushnell, neither his statements nor your statements >are "nonsense" except your opinion that his statement on Wh is nonsense. > >In fact, on page 121 of the BIPM Brochure, we find that the joule is >*defined* as the newton meter, not as the watt second, as you imply. > >The watt second, an equivalent but less fundamental form of the joule, >and the watt hour, not even a coherent SI form, are not even mentioned >in this CIPM Resolution of 1946. > >Contrary to your implication, Bob does not assert that the joule, the >watt, and the watt second are exclusively for electrical applications. > >Bob's statements are clear. The joule is preferred for all forms >of energy. However, Bob would "allow" the watt hour only for its >traditional use; for the measurement of *electrical* energy. > >If I had the authority, I would declare the watt hour illegal by a date >certain for any kind of energy bought or sold in interstate commerce. > >Gene. >.......................................... >> Robert Bushnell wrote on July 12 > >> >Madan; ... you tell Claire to give energy in units of TWH. >> > >> >This is wrong. The watt hour is allowed only for electricity. >> > >> >Energy is given in multiples of joule... > >Joe Reid responded on July 12: >> Nonsense! The watt is the SI derived unit for all kinds of power - >> mechanical, electrical or thermal. Agreed that the joule is the SI >> derived unit of energy and is equal to the watt second, again not >> exclusively electrical. The watt hour is a non-SI unit accepted for >> use with the International System... Joseph B.Reid 17 Glebe Road West Toronto M5P 1C8 Tel. 416 486-6071
