2003-01-01 In the case of the unit 'joules per hour per kilogram' it is obvious the real unit should be watts per kilogram. But, there are cases where compound units can not be reduced as such. In order to correctly answer Pat's question about proper arrangement of unit symbols, we need to address these issues.
First of all, in the example Pat gave below, in proper SI, the unit name should never appear or be read as joules per hour per kilogram. The word per should only appear one. The unit should read as joule(s) per kilogram hour. The symbol would be J/kg.h The word per and the solidus symbol divides the units in the numerator from those in the denominator. If we wanted to express the unit watts per kelvin (W/K) in base units, we would have kilogram metre(s) cubed per second cubed kelvin, or in symbols: kg.m^3/s^3.K or kg.m^3.s^-3.K^-1. Since the kelvin is to the right of the solidus, it can not be mistaken as part of the numerator, such as kg.K.m^3/s^3. This way it is clear, concise and coherent. The multiple use of the word "per" is a bad habit carried over from FFU. Part of metrication must be to clean house and clean house means getting rid of bad and wrong habits that are part of FFU. In some cases, units can be grouped in parentheses, but this is not really necessary if the rule is adhered to. Always remember to keep it simple. Just because everyone else wants to make it hard, does not mean we have to follow that example. John ----- Original Message ----- From: "Gene Mechtly" <[EMAIL PROTECTED]> To: "U.S. Metric Association" <[EMAIL PROTECTED]> Cc: "U.S. Metric Association" <[EMAIL PROTECTED]> Sent: Wednesday, 2003-01-01 13:04 Subject: [USMA:24306] Power over Mass > On Wed, 1 Jan 2003, Pat Naughtin wrote: > > > Dear Jim, > > > > The other day I was reading a popular text that contained a unit that > > described the energy needed for various sports. I translated the unit the > > authors used into SI as 'joules per hour per kilogram or J/h/kg'... > > > > What would you recommend in these circumstances? > > What are the *average* numerical values for each sport in W/kg or mW/kg? > > Query from neither Jim McCracken nor Jim Frysinger, > but from Gene. >
