In Praise of Dimensional Analysis

glen herrmannsfeldt wrote:
> Jerry Avins wrote:
> 
> (snip)
> 
>> Miles/hour/second is a pretty common unit. Of course, an hour-second 
>> equals a square minute. :-)
> 
> One of my least favorite units is the one power companies like
> to use to describe usage:  Kilowatt hours/day.  Kilowatt seems
> like a fine power unit, without an extra factor of 24.

I think you mean that a KW-hour is a unit of energy. It is also 
(indirectly) a unit of revenue. Hence the usage.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Jerry Avins wrote:
> glen herrmannsfeldt wrote:

Glen,

Your timestamp seems to be a bit into the future.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Jerry Avins wrote:
> glen herrmannsfeldt wrote:
>> Jerry Avins wrote:
>>
>> (snip)
>>
>>> Miles/hour/second is a pretty common unit. Of course, an hour-second 
>>> equals a square minute. :-)
>>
>> One of my least favorite units is the one power companies like
>> to use to describe usage:  Kilowatt hours/day.  Kilowatt seems
>> like a fine power unit, without an extra factor of 24.
> 
> I think you mean that a KW-hour is a unit of energy.

No, you meant that KW-hr/day is a unit of power. My mistake.

   ...

Jerry
-- 
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

On Sun, 29 Apr 2007 18:09:45 -0400, Jerry Avins <jya@ieee.org> wrote:

>Jerry Avins wrote:
>> glen herrmannsfeldt wrote:
>
>Glen,
>
>Your timestamp seems to be a bit into the future.
>
>Jerry

But are the units right?

;)

Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.ericjacobsen.org

glen herrmannsfeldt wrote:
> Jerry Avins wrote:
> 
> (snip)
> 
>> Miles/hour/second is a pretty common unit. Of course, an hour-second 
>> equals a square minute. :-)
> 
> One of my least favorite units is the one power companies like
> to use to describe usage:  Kilowatt hours/day.  Kilowatt seems
> like a fine power unit, without an extra factor of 24.
> 
> -- glen
> 
Unfortunate for technical people, but good for 'normal' customers.

Everyone knows what a day is, and we all get billed in KW-hours.  I 
doubt that very many people could tell you that a KW-hour/day is a hair 
under 42 watts, and even fewer could do it in a blink without a calculator.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google?  See http://cfaj.freeshell.org/google/

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

On Sun, 29 Apr 2007 14:29:36 -0800, glen herrmannsfeldt
<gah@ugcs.caltech.edu> wrote:

>Jonathan Kirwan wrote:
>(snip)
>
>> A venerable approach.  Galileo used it, in fact.  Algebra, at the
>> time, he felt was not yet rigorously founded while ratios had been for
>> quite some time.
>
>I had known that Galileo's first experiments with rolling balls
>were an attempt to slow down the fall of gravity, and allow him
>to understand the effect.  I hadn't known why he decided to do it
>that way, without the algebra to show what the result would mean.

Galileo probably began considering motion like this at least as early
as 1586, I think, having written a dialogue on problems of motion that
year.  He must have considered inclined plane experiments as early as
1591, since he added them to his De Motu that year.  But I seem to
recall that his immersion into building them would have been around
1601-1602.

The details about his thinking, as well as copies of some of his
folios, can be found in Sillman Drake's "Galileo: Pioneer Scientist."
I recommend it.

Jon