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Re: operational F, m, and a (velocity measurements with fish-scal es)





At 05:09 PM 10/19/01 -0500, RAUBER, JOEL wrote:
one cannot use the spring to measure other forces, ***without other
kinematical measurements***

1) I am mystified by the reference to "other" forces.
What other forces? Other than what?


The one's which you are trying to measure. (see RESET post)

The spring-scale is advertised to measure the force applied to its
hook. Nothing more, nothing less.

When using it to measure another force, the advertisement works when you
place the spring force on the hook in equilibrium with the other force that
the hook is attached to.

(There will of course be
imperfections
and nonidealities, but that doesn't change the concept.)


Correct. The nonidealities aren't at issues as I have repeated ad nauseum.

I will agree that a spring-scale here on my desk doesn't
measure the force
between Alpha Centauri and Beta Centauri, or any "other"
force, other than
the force applied to its hook. But that really ought to go without
saying. What is the point of discussing this?


(see RESET)

2) I am totally mystified by the emphasized words, "without other
kinematical measurements" (henceforth WOKM).


The emphasize is because your examples have all tended to deny the need to
know kinematical information about the pointer when using a spring scale,
other than its position.

I have given an example (scale + scale + chassis) wherein a
scale measures
a force WOKM. The reading on the scale tells you the force WOKM.

Perhaps WOKM is some general philosophical statement. If the
point is that
you cannot measure mass WOKM or length WOKM or time WOKM or
temperature
WOKM or color WOKM, then by extension you cannot measure
force WOKM -- but
this doesn't tell us anything interesting about force _per
se_. So once
again I'm wondering what is the point of discussing this?

=============

I have described a fully-realizable physics experiment that
illustrates
what I mean (scale + scale + chassis). The counterarguments
have uniformly
lacked any experimental or theoretical _physics_ rationale.

The example added nothing to the discussion beyond what the original fish
scales added to the discussion. It in fact totally ignored the question of
using these spring-scales to determine forces and it ignores the question of
the pointers that these gedanken spring-scales must have in order to
operate.

You never did reply to the question about the instructions you give your lab
technician on how to operate the spring-scale in an operational manner.

Unless
somebody adduces a _physics_ reason to believe otherwise, I
will continue
to believe my spring-scale can measure a force WOKM,

Except, you never have said how? And remember, I am talking about using it
to measure some other force, not the trivial statement that the
instantaneous position of the pointer measures the force the spring applies
to the hook. You have somehow taken what I have said to mean that; I don't
mean that, and apoligize if that point wasn't clear.

The whole discussion was interesting to me as it pertained to using
equilibrium measurements to measure forces as an alternative to using
acceleration to measure forces as pertains to the whole fundamentals of F=ma
discussion. (see reset post)