Measurements

[Pigwidgeon]

--- In HPFGU-OTChatter at y..., "Amy Z" <aiz24 at h...> wrote:
> Haggridd wrote:
> 
> > The meter, in contradisinction, is some 
> > fraction 
> > > of the distance from the north pole to the equator on a line 
> > passing 
> > > through Paris.  BLECCH!!
> 
> Jenny wrote:
> 
> >Oh 
> > yes, meter is the distance light travels in one second, because 
it 
> > doesn't always go excatly the same distance
> 
> It's actually =derived= from the distance light travels in a 
second; 
> light moves a LOT faster than 1 m/s (so does sound, or a thrown 
> baseball, for that matter).
> 
> My Science Desk Reference says:
> 
> "The first [SI metric system] measurement, the meter, was based on 
the 
> circumference of the Earth measured on a line through Paris and the 
> north and south poles.  The line was divided by 40,000,000, and 
each 
> division was called a meter . . . . Later, the meter was further 
> defined as the length equal to 1,650,763.73 tiemsthe wavelength of 
> orange light emitted when a gas consisting of a pure isotope of 
> krypton (mass number 86) is excited in an electrical discharge.  In 
> 1983, the waavelength definition was replaced the the distance 
light 
> travels in a vacuum in 1/299,792,458 second".
> 
> Paris may be arbitrary, but at least it was a good choice.  I mean, 
> they could have made it Newark.

It was not an arbitary choice. AFAIK the French were unhappy with 
using the British mile and so decided to invent their own unit of 
distance. It was then calculated, as above described by Amy. The fact 
that they got the measurement wrong seems to have been overlooked in 
more recent time.


Light travels at speed c=300,000,000 m/s
Sound travels at about 330 m/s
A top sprinter averages 10 m/s for 200 metres.



Simon