[ausev] A Joule is a watt-second

[Gil Dawson]

Hi, Brian--

Thanks for the cogent reminder that this correspondence is neither an  
accident nor an approximation, but a definition.

It seemed odd at first that pushing and shoving would be related  
precisely to voltage and amperes, but I suppose that the SI people  
must have defined volts and amps in terms of joules and seconds, so  
that the precision is not a coincidence at all.

--Gil


On Jan 5, 2009, at 2:36 P, Brian Lasseter wrote:

> On Mon, Jan 5, 2009 at 12:19 PM, Gil Dawson <Gil at gil.dawson.name>  
> wrote:
>>  From http://www.batesville.k12.in.us/Physics/ANet/Science/Measure/
>> UnitsDictF2J.html
>>
>>> JOULE (J)
>>>     The SI unit of energy. One joule is the work done by 1 newton
>>> acting through a distance of 1 meter. One joule equals (1) 1 watt-
>>> second;...
>>
>> A rather odd coincidence, wouldn't you think?  They must've fudged
>> the whole SI system to make this work out.
>
> There is nothing coincidental or fudged in the SI system.  SI derived
> units are all defined in terms of SI base units and/or other SI
> derived units.  The watt happens to be defined in terms of joules (not
> volts or amps).
>
> - meter, kilogram, and second are SI base units.
> - The newton is the SI derived unit of force, equal to the amount of
> force required to give a mass of 1 kilogram an acceleration of 1 meter
> per second squared.
> - The joule is the derived unit of energy, equal to a force of 1
> newton traveling through a distance of 1 meter.
> - The watt is the SI derived unit of power, equal to 1 joule of energy
> per second.
>
>
> http://en.wikipedia.org/wiki/SI_base_unit
> http://en.wikipedia.org/wiki/SI_derived_unit
>
>
> -- 
> TTFN,
> Brian "Lasso" Lasseter
>
> "No Sane man will dance."   -Cicero (106-43 B.C.)
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