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

In response to John D:

Round 3: ding ding!

At 10:01 AM 10/19/01 -0500, RAUBER, JOEL wrote:

I'm willing to stipulate an arbitrarily well lubricated excellently
designed ideal scale.

Good, that simplifies the discussion. Call that approximation /1/.

The gamma v term isn't present when you make an ideal reading, as you
measure v to be zero.

No, I don't. That's not my definition of ideal. Maybe YOU insist on
observing v to be zero, but I don't.

My very next sentence (below) makes it clear that I don't insist on that as
a definition of ideal. And I hope made it clear that I understood that that
may not be your definition of ideal, and that you have constructed a way to
operate the device in a different manner. But perhaps it didn't make it
clear.


Or you at least had to measure v to make your corrections.

No corrections are necessary because of approximation /1/.
So once again,
this is not a reason for worrying about v.

This I don't understand without further explanation.

a) Are you saying that approx /1/ implies no velocity measurement?


4) It may be inconvenient for you to make an observation when
the velocity
is nonzero, but Hooke's law still applies whether you find it
convenient or
not. You can make things more convenient by making a movie
and analysing
it frame-by-frame later, to find the value of (x) as a
function of time....
Hooke's law is applicable to any (x), whether or not (x)
is constant.


True. If I understand you correctly, you are saying that in
order to use
the spring scale I do not have to line of the pointer next
to the tick marks
in such a way that their relative velocities are zero.

That's what I'm saying.

We agree that this is highly incovenient,

OK.

and not what one does in practice with spring scales;

Maybe it's not what YOU do with spring scales, but you can't
require others
to follow the same practices as you.

You are implying something I didn't say. I never said I was requiring you
to operate the scale in that manner, as my very next sentence clarifies
(omited in your quote ) I reproduce it here,

"however as a matter of principle I suppose this is possible."

Thereby, admitting that you can operate the scale in the fashion you
indicated (not requiring a v=0 meaurement, in contradistinction to common
practice.)


However,

a) We are still required to make a velocity measurement (and
perhaps even
acceleration measurements), as a matter of principle in
operating the device
in that matter. I don't think one can escape that reality.

This has been repeatedly asserted, but no experimental evidence or
theoretical support has been given. Re-asserting it won't help.

And neither does simply re-asserting the contrary help either.

In fact I have offered evidence, which I'll repeat in a paraphrase.

The experimental evidence is the evidence of how everyone I have ever
chatted with uses a spring scale. They line up the pointer such that it has
zero velocity relative to the tick marks, are you suggesting that this isn't
the common way of operating the apparatus? (you have offered another method,
that still involved velocity measurements and acceleration measurements in
order to back calculate the spring force K*x, but at least your alternative
didn't require the velocity measurement to be zero).


I suspect this is an axiomatic assumption in JR's world-view.
If so, we
have nothing to discuss. I don't want to get into a religious
discussion. You can make whatever axiomatic assumptions you
like; I don't
have to agree.

It is not an axiomatic assumption. It is a description of how one uses the
apparatus, either in actual common practice, or in the theoretical
(gedanken) usage of an ideal fish-scale for the developement of a force
measuring apparatus standard.


b) I'd even question whether or not you were using the device for an
equilibrium determination of force.

(If the answer is it is not an equilibrium determination), then that
terminates the discussion as we are discussing equilibrium
determinations
and whether or not they implicitly involve acceleration (to
be discussed
later).

I'll let you have this both ways. The spring-scale gives a reading of
force WHETHER OR NOT things are in equilibrium. Equilibrium has got
nothing to do with it.


Maybe you want to make an equilibrium measurement. Fine. Do
whatever you
like. But you cannot prevent me from making equilibrium AND
non-equilibrium measurements.


And since I offered statements regarding either equilibrium or
non-equilibrium measurements, I haven't prevented you from operating the
scale in either manner and have allowed that either can be done.

Of course, this discussion comes about because of the question as to whether
or not there are acceleration independent means of measuring forces. One
poster offered up a statement that Sommerfeld described *equilibrium*
methods as a possibility. The spring scale is an obvious metaphor for this,
and excellent gedanken tool for analysing these questions. Indeed, you gave
an elegant description of developing a spring scale standard with a single
tick mark. (I suspect, but I don't know, that such a standard would require
equilibrium measurements to be useful; but I imagine that you can invent
other similar standards for non-equilibrium measurements as well, I imagine
that they would require more than one tick mark.)

Hence it is germane to the discussion whether or not you are operating the
spring scale in an equilibrium manner or not.

If you are operating it in an equilibrium manner, have you not made a
velocity measurement of the pointer relative to the tick-mark scale?

OTOH, If you operate in a non-equilibrium manner, your description referred
to making velocity and acceleration measurements in order to be able to
calculate K*x; (particularly using the rubrik of the videotape and looking
at it frame by frame to make those measurements).