Mass and Weight Units

[Frederick G Scoles]

On Thu, 3 Aug 1995, Vince Mrykalo wrote:

>
> > courses.  The gram which is taught in measurement labs is usually the
> > "apparent gram", meaning that it is approximate to a true gram but has
> > corrections for the gravitational force and barometric pressure (air
> > buoyancy) for the particular altitude of measurement.  Unfortunately, it
> > is difficult to measure a true gram of mass unless one is in a good
> > vacuum and has corrected for gravity.
The difference between a gram (mass) and the "apparent" gram (corrected
for air bouancy or barometric pressure) is usually quite small, approx.
10 to 20 parts per million.  This difference will show up in the 4th or
5th digit.  The main thing I wanted to show is that since the gram as we
all use it has already been corrected for the force vectors (bouancy or
barometer, and gravity or altitude), then it really makes little
difference which unit we weigh action parts in, as long as we are
consistent and keep our balances calibrated.

> This is pretty interesting, but what kind of differences in the gram are we
> looking at from one clime to another?> ---
Swiss made (Mettler) weights are about 5 to 7 ppm different from Troemner
(Phila.) wts., which causes a big problem only with analytical or better
balances (0.0001g or better).  I used this example to show how gravity
and air corrections have been an integral part of the gram as we use it.
So, when a teacher says the gram is a unit of mass, that is only part of
the story.
Fred Scoles RPT
> vince mrykalo  rpt
>
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> The facts all contribute only to setting the problem, not to
> its solution -
> Ludwig Wittgenstein
>
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>