James Frysinger wrote in USMA 19078: >"Joseph B. Reid" wrote: >> >> Bill Hooper wrote in USMA 19071: >> >> >The watt is also equal to a volt-ampere but that is not it's original >> >definition. The watt is originally defined as a joule per second. Since the >> >volt (V) is a joule per coulomb (J/C) and the coulomb (C) is defined as an >> >ampere-second (A�s), it is easy to show that the volt-ampere equals the >> >watt: >> >1 V�A = (1 J/C)�(1 A) = (1 J/A�s)�(1 A) = 1 J�s = 1 W >> > >> >(In proper SI, multiplication of units is shown by the raised dot. The >> >raised dot generated by my computer is shown here >> >between the letters X and Y: >> >> Bill has brought volts, coulombs and amperes into the discussion. Those >> are electrical units. The watt is defined in terms of length, mass and >> time (m2.kg/s3). The same is true of the joule (m2.kg/s2) > > It's a moot point, Joe. Energy is energy and power is power. > > For didactic purposes or for definition one may choose to start with >mechanical and then show that they apply in electrical situations or >vice versa. Classical physics courses start with mechanical, but that's >based on historical reasons as well as the likelihood that students find >mechanics easier to start with. > > People have worked hard to show the equivalence among mechanical, >electrostatic, and magnetic units. Let's not migrate back to three >separate metric systems.
I quite agree. My point was that the watt is a unit of mechanical power as well as an electrical unit. That may be news to average Americans. Joseph B.Reid 17 Glebe Road West Toronto M5P 1C8 TEL. 416-486-6071
