Re: Metric Time (was Re: Why not 13 months? (Was La Systeme Metrique))

Olaf Seibert (
14 Oct 1995 02:16:35 GMT

In <45ctmn$> (Andrew Reid) writes:
| But you can get into trouble when these criteria give different
| answers -- my personal favourite example is pressure. The SI unit of
| pressure, the Pascal, is one Newton per square metre, that is to say,
| one kilogram per second-squared per metre. It's a derived unit,
| obviously, but the problem is that for the obvious day-to-day pressure
| measurement, it seems to me that the obvious earth-centred unit is
| the International Standard Atmosphere. It has all the alleged advantages
| of a metric unit, being more-or-less unit-sized in the conventional
| range. In spite of my rigorous metric education, I have no idea how
| many Pascals the atmospheric pressure is, I think it's a few hundred

This is actually pretty easy. 1 atmosphere is almost exactly equal to
the pressure by a column of 10 m of water, as every diver should know.
And I'm not even a diver :). A quick calculation then reveals that a
column of 1x1x10 m of water is 10,000 kg so it produces a pressure of
about 100,000 N (per m2).

A "bar", often used in wheather forecasts, is about the same as an
atmosphere, wich makes a millibar the same as a hectopascal.

| The Celsius temperature scale has a similar, though less serious,
| flaw, in that it is thoroughly arbitrary. It does have the advantage
| that most scientists use it or the closely-related Kelvin scale,
| but the water-oriented zero and hundred marks are not notably more
| intuitive than the Farenheit(sp?) scale, which has the intuitive
| advantage (as I learned in our recent Chicago heat wave...) that
| 100 F is getting to be uncomfortably warm, and 0 F is getting to be
| dangerously cold. So it actually *does* make a certain kind of
| sense.

As far as I know, the definition of 0 Fahrenheit is the freezing point
of a saturated solution of salt in water. 100 F is defined as human (?)
body temperature under certain conditions (which apparently makes the
normal body temperature slightly less than 100 F). I would not find
this a very consistent system; the definitions of 0 C and 100 C at
least are defined in a manner related to each other.


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