On Jan 22, 12:57, Max Eskin wrote:
> Subject: Re: OT: Alien Media (was Disasters and Recovery)
> Philip.Belben_at_pgen.com wrote:
> > Metre, Kilogram, Second, Ampere, Kelvin, Mole and Candela (normally
>
> Kilogram? Why not gram?
The whole system is based on units that are matched to each other in such a
way that the constants involved in relating units to other units work out
to unity. So the kilogram just happens to be a handier quantity than a
gram, and saves a lot of dividing or multiplying by 1000. Except, of
course, in real life, where units are rarely handy sizes at all :-)
On Jan 22, 13:28, Cameron Kaiser wrote:
> Subject: Re: OT: Alien Media (was Disasters and Recovery)
> :: Uh, I thought a gram was defined as 1 cc of water at 4C. A kilogram
is
> ::1,000 cc of water at 4C, which is one litre of water (a litre being
1,000 cc
> ::volume).
>
> The original kilo is a big lump of metal in a bell jar, when the kilogram
> was introduced as a standard.
It was originally intended to be a cubic decimetre of water at it's maximum
density. Unfortunatley, that turned out to be 28 ppm to large -- the
constants I mentioned above don't quite work out to unity. So it was
changed to an arbitrary amount to suit -- and the litre was defined as the
volume of water that had that mass at it's maximum density. Hence a litre
was actually 1000.028 cm^3. Since that just moves the "obviously silly"
constant to a different place in the scheme, it was redefined later to be
exactly 1000 cm^3, but with the recommendation that it not be used for work
of high accuracy. Hmmm.... and we thought IBM were having trouble with
the megamaths.
--
Pete Peter Turnbull
Dept. of Computer Science
University of York
Received on Fri Jan 22 1999 - 16:54:43 GMT