Sorry I misused the term weight for mass. It's an example of a common
practice in the public arena use of terms which those of us who are not
deeply entrenched in the SI must overcome.
Regards, Stan Doore
----- Original Message -----
From: <[EMAIL PROTECTED]>
To: "U.S. Metric Association" <[email protected]>
Sent: Saturday, September 01, 2007 8:26 PM
Subject: [USMA:39314] Mass and Weight in Jakuba Book
Stan,
In Classical Mechanics, position, speed, and acceleration *must* be with
respect to a particular "frame of reference"; that is, with respect to a
particular "coordinate system" if position, speed, acceleration, *and
weight* are to be measured without ambiguity. There must be an origin, and
definitions of three coordinates (rectangular, cylindrical, spherical, or
three coordinates from some other of more than ten sets) for locating
positions in space.
Classically (no speeds of physical objects approaching c, the speed of
light), mass is independent of position, speed, and acceleration. In this
case, one may write force = mass times acceleration, Newton's Second Law
in its most simple form.
However, weight (defined in SI as mass x acceleration of gravity)
*requires* either specification or unambiguous knowledge of the particular
frame of reference in question.
This necessary requirement for a "frame of reference" is *missing* in your
discussion of mass and weight.
A useful illustration of weight variations with respect to different
"frames of reference" is the fact that an earth orbiting astronaut is
nearly weightless in the reference frame of the spacecraft, but is not
weightless in the frame having its origin at the center of the earth. The
weight of the astronaut is reduced by only a small amount when in near
earth orbit wrt the earth. A larger reduction to about 1/6 the value on
earth wrt the earth arises in close orbit around the moon or on the
surface of the moon in the frame with its origin at the center of the
moon.
Gene Mechtly.
---- Original message ----
Date: Thu, 30 Aug 2007 08:16:48 -0400
From: "Stan Jakuba" <[EMAIL PROTECTED]>
Subject: [USMA:39292] Re: Current version of PCI list
To: "U.S. Metric Association" <[email protected]>
...
Attached please find the subject coverage as it is presented in my book
(pages 24 thru
31 if you have it).
