[amsat-bb] Re: AMSAT-NA totally metric?
n8fgv at usa.net
Sun Jan 21 14:58:09 PST 2007
>NASA has finally agreed to fly to the moon in metric - a
>move its scientists have wanted ever since they mixed up
>kilometres with miles and crashed an expensive spacecraft
The actual mixup was pounds (of force) and Newtons, and the JPL trajectory
analysts knew that the spacecraft was off course but their managers would not
listen to them when they said that a course correction was needed. That was
real cause of the accident. Moral of the story: when your highly educated
expert employee tells you that he doesn't understand what is going on, you
better drop everything and get to the bottom of the mystery before disaster
>On the other hand many caculations are simplified with metrics,
>wavelength for example. Amps, Volts, Farads, Henrys, Ohms,
>Frequency, and Watts are same in metric and need no conversion.
The electrical units are NOT "the same in metric", they ARE metric!!!
My pet metric peeves:
Newspaper and magazine editors (probably English majors) who quote excessive
precision when converting from metric to US units, as in "the asteroid is
estimated to have a diameter of 1000 kilometers (620 miles)". The scientist
they interviewed does not know the diameter to more than one significant
figure, so quoting 620 miles is absurd.
The same editors also convert rocket thrust from pounds (of force) into
kilograms, because they don't know that pounds can measure mass or force and
these ARE NOT THE SAME THING! In respected scientific publications I see
statements such as "the 100 pound (45.3 kilogram) rocket thrusters..." when
they SHOULD have written "the 100 pound (400 Newton) rocket thrusters....".
As a teaching assistant in the freshman "physics for pharmacists" class I was
required to teach the international students about feet, inches, pounds and
miles when I should have been teaching the US students how to do physics in
It is however a fact of life that both systems of units will be around for
quite some time, and engineers in the United States need to be fully
conversant in both systems of measurements. And if I find a nice South Bend
lathe on E-bay I'm not going to pass it up just because it wasn't made for
Dan Schultz N8FGV
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