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Re: Feeling Acceleration




I've been sitting on the sidelines, amused by the irrelevance of much of
this thread.

Does an ammeter measure current? If it is of the electromagnetic needle
type its needle is responding to a force, caused by the effect of a
magnetic field upon chrages going through its coil. If it is of the type
in an automobile I once owned, it is responding to the expansion of a
bimetallic strip through which a current passes. Does a sensitive
coulommeter measure charge? It measures the force from charges. Does a
graduated cylinder masure volume? It measures the height of liquid in the
cylinder. (Try using it to measure the volume of a gas.) And so it goes.
While all of this disussion helps us understand the various instruments
which respond to a physical property (which is good) I find it puzzling
that they are often couched in language which tries to suggest that one
description of the device is "right" and another "less right".

Almost all of our measuring instruments measure a secondary effect of the
thing we claim to be measuring. And if we don't use them properly, we can
fool ourselves. (Watch out when using voltmeters and ammeters in regions
where there's a magnetic field, and don't wipe the meter face to give it
an electrostatic charge.) Most every instrument has limiting conditions
of use. Many needle-type analog instruments (even expensive) ones only
read correctly only when upright (or only when lying on their backs),
which is a good reason to keep and read the instruction manuals.

The mistake is philosophical, and lies in our confusing the indicaton
(reading) of an instrument (or a feeling in our bodies communicated to our
brains) with the actual physical quantity which initiates the chain of
events leading to that reading.

-- Donald

......................................................................
Dr. Donald E. Simanek Office: 717-893-2079
Prof. of Physics Internet: dsimanek@eagle.lhup.edu
Lock Haven University, Lock Haven, PA. 17745 CIS: 73147,2166
Home page: http://www.lhup.edu/~dsimanek FAX: 717-893-2047
......................................................................


On Wed, 9 Apr 1997, Eugene P. Mosca wrote:


...
2) I've never seen a force sensor yet that doesn't work by first measuring
acceleration.
...

Is there a consensus on this list on the validity of this statement? It
has been made repeatedly before, and as far as I recall, without
challenge. I would really like to know, because if there is a consensus
in its favor, further discussion of the matter is rather pointless.


If a spring scale is a sensor then it seems to me that it measures a force
without first measuring an acceleration.

Gene
----------------------------------------------------------------
Eugene (Gene) P. Mosca Phone 410-293-6659 (Fax 3729)
Physics Department 410-267-0144 Home
572 Holloway Road 610-683-3597 Summer
U.S.Naval Academy Mailstop 9C, Michelson Rm 339
Annapolis MD 21402 email: mosca@nadn.navy.mil
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