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Operational Definitions



At 11:33 AM +0300 4/10/97, Igal Galili wrote:
Just a comment. For years I have been advocating the change of the
gravitational definition of weight (gravitational force) in favor of its
operational definition: the result of standard weighing - the force applied
on the support.

This particular example doesn't seem so bad, but I'm wary of operational
definitions in general. My science education professor once asked us in
class what the definition of temperature was and a PhD physicist taking the
class with me responded with usual stuff about average kinetic energy. The
Sci Ed prof said no, and no other student could come up with any other
definitions. So after class I asked him what _real_ the definition of
temperature was and he said, "It is how hot or cold an object feels." So
if I put my left hand in a bucket of cold water and my right hand in a
bucket of hot water, and then simultaneously plunge them both in a bucket
of warm water, the middle bucket has two different temperatures at the same
time? And objects that aren't being felt have no temperature? Does an
object that isn't being weighed at some instant of time have weight then?

Larry Smith

P.S. I agree with Donald Simaneck's post quoted below:

Do we feel temperature? No, we feel the result of heat transfer from an
object to our skin, stimulating nerve impulses which .... No wonder early
physicists were in some confsion between heat and temperature as physical
concepts. Do our eyes see light? No, they sense the coded firing of
electro-chemical nerve impulses resulting from a chemical change in
receptors in the retina.

And you folks can surely suggest more examples. All of our so-called
basic and fundamental physical properties are indirectly measured by
instruments and indirectly sensed by our bodies. And many of our
*concepts*, such as energy, momentum, fields, etc. are at least one step
further removed from reality.

I think we are asking for trouble when we teachers try to relate physical
concepts to things people sense and feel--unless we are willing to turn
your courses into physiology courses by carefully examining the
biiological chain of events between the physical stimuli and the response
processed by the brain. Of course the sensory feelings are a first step
for students, and were a first step historically in the development of
physics. But we must go beyond that first step to get to physics.

One of the reasons physics has succeeded as an independent discipline is
that, over its long history, it was able to separate the physics from our
feelings, to make objective models rather than egocentric models, and to
realize that we seek understanding of a universe which we assume
represents an objective reality, not a subjective impression, and which
does its thing without regard to how we feel about it or how we'd like it
to be. We ought to make students aware of that. Many other areas of human
thought, including some which call themselves "sciences", are still making
the sort of mistakes of methodology which physics learned to avoid long
ago by taking a more objective approach.