John,
Although you may be forgiven(?) for quoting Jim's non-SI value, you too do not
include the power of the gas grill in watts. What is it? Why burden the readers
to convert to SI?
Gene
p.s. I do have highest regard for the postings of both of you relative to
postings by other subscribers in spite of this rare deviation from SI.
---- Original message ----
>Date: Tue, 8 Jun 2010 18:59:49 -0700 (PDT)
>From: "John M. Steele" <[email protected]>
>Subject: [USMA:47581] Re: One unit only
>To: "U.S. Metric Association" <[email protected]>
>Cc: "U.S. Metric Association" <[email protected]>
>
> Jim,
>
> I agree with glassy-eyed and wobbly kneed, but this
> is the ROOT of all energy vs power confusion.
>
> Just ask, "So, after the grill has consumed 15000
> BTU, it dies? That seems like a lot of money for a
> grill with a one hour life."
>
> I'm afraid it is up to the engineers to be
> persistent PITAs on this matter. Proud to serve. :)
>
> ------------------------------------------------
>
> From: James R. Frysinger <[email protected]>
> To: [email protected]
> Cc: U.S. Metric Association <[email protected]>
> Sent: Tue, June 8, 2010 9:47:38 PM
> Subject: Re: [USMA:47579] Re: One unit only
> John, your last paragraph can be exemplified with
> the ratings that one sees posted for gas grills.
> They are usually rated as being, for example, "15
> 000 BTU". What is meant, though, is "15 000 Btu/h"
> -- where I have fixed the error in the symbol and
> have added the divisor. The former is an energy
> value; the latter is a power value (the rate at
> which chemical energy is converted to thermal
> energy).
>
> Caution: Experience has shown that if I try to
> discuss this with the sales staff, they get
> glassy-eyed and start to look wobbly in the knees.
>
> Jim
>
> John M. Steele wrote:
> > Pat,
> > I'm sorry but I must go back to your statement to
> Stan, " It seems really odd to me that engineers,
> who
> > > probably know much better, are using a power
> unit
> > > when they are referring to energy."
> > In the instance you cite, you are talking about
> energy over a time period, and energy divided by
> time is power. Annual energy usage has a dimension
> of power, whether you use power units (watts) or
> explicitly describe the energy and the time period.
> > Stan is at least technically correct in using
> watts. I have some misgivings about average power
> vs peak power if the situation is not fully
> explained.
> > Power and energy have exactly the same
> relationship between them as velocity and distance.
> If either is described fully as a time function, I
> can derive the other. Since I am retired, I drive
> much less. Pardon the miles, but they are
> unfortunately the units on my odometer. I am only
> driving 4000 - 4500 miles per year. As there are
> 8760 hours in a common year, my average speed is
> circa 0.5 MPH. That, of course is completely
> useless as a description of my driving which is
> normally at 25 - 75 MPH, plus many hours with the
> ignition is off. My miles per annum is a speed
> (just not terrible useful). 0.5 MPH or 4400
> miles/annum encodes the same information.
> > In the same sense 1600 PJ/annum and 50.7 GW
> encode the same information. As I don't know how
> evenly the 1600 PJ of coal is burnt over the year,
> the utility of average power may be debatable but it
> is technically correct. When energy usage over a
> period is described, the period is so intimately
> attached to the energy that it would be better to
> drop both units than only one.
> > I do understand that you meant petajoules per
> annum, but I believe that omitting the per annum has
> lead to some of the confusion that has existed here
> in various notes about energy vs. power. It must be
> completely explicit, or at least that is my view on
> the matter.
> >...
