Date:         Wed, 8 Oct 2008 13:36:52 -0700
Reply-To:     Keith Hughes <keithahughes@QWEST.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Keith Hughes <keithahughes@QWEST.NET>
Subject:      Re: Magical cast iron suspension?
In-Reply-To:  <20081008194602.9452A580C05@mpls-mf-13.inet.qwest.net>
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>
> Date:    Wed, 8 Oct 2008 11:12:15 -0600
> From:    Andrew Grebneff <goose1047@GMAIL.COM>
> Subject: Re: Magical cast iron suspension?
>
>
> .It would be an interesting idea... any listees out there
> with accurate scales? Mass a fabricated arm, mass a cast arm; then
> mass each END of each arm separately and let the list know the
> results. I say mass, because despite "common knowledge", scales don't
> measure weight, they measure mass
Uhmmm...no they absolutely do *Not* measure mass.  They measure weight,
which is more accurately referred to as *force* - i.e. the acceleration
force on the mass due to gravity - and from which one can calculate the
"apparent" mass of the object.  Scales/balances also do not correct for
air buoyancy, an effect that becomes more pronounced as the *density* of
the weighed object decreases, and one which must be addressed when
calculating apparent mass.  Because of these buoyant effects, you also
have to stipulate the reference density (typically 8.0gm/cc in the US -
e.g., object A has an "apparent mass of 10g based on a density of
8.0gm/cc", which means that object A would "weigh" the same, under the
same conditions, as Object B that has an actual *mass* of 10g, and a
density of 8.0gm/cc).  To get actual mass, in a direct measurement - not
using substitution methods - you also need to factor in longitude and
elevation of the measurement point.  The density of the earth is not
uniform so the acceleration due to gravity is not uniform, and since the
force weakens as the inverse square of the distance from the effective
center of mass, the elevation will change the apparent mass as well.
>  (kilograms & pounds are a measure of
> mass;
True, at least partially.  "Pounds" as typically used is a measure of
weight or force, not mass.  As a unit, it certainly can be used for
mass, but usually isn't.
>  newton-meters & foot-pounds are a measure of weight
Sorry, but no.  They are a measure of either *work*, or *torque*.

Keith Hughes
'86 Westy Tiico (Marvin)