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Re: [Phys-l] Inertia?



Of course inertia becomes another name for impetus. Minds on Physics does
not use inertia, though it may mention the word. I would agree that it is
an ill defined word which is better left out. Students need to learn about
interactions and the idea that forces are necessary to observer changes in
velocity. Incidentally apparently Aristotle noted that things would
continue moving unless something acts to stop them, but the concept never
stuck until Galileo.

I would also put the word gravity in the same class as inertia. Both are
magical incantations used to explain things.

However it is possible to take common ideas and bend them to make physics
sense. As I recall there is a good AJP article about doing this. So maybe
one should say that bowling balls have momentum rather than inertia. Then
the momentum stays until an interaction transfers it to another object.
Impetus/inertia becomes momentum, which can then be quantified and molded
into a physics concept.

John M. Clement
Houston, TX


I have a different problem with the word "inertia." If you ask
someone why a bowling ball rolls down the alley although no one is
pushing it, they are liable to say "inertia," in the sense that it is
the cause of the continued motion. On those grounds alone I would
argue for avoiding it.

joe

Joseph J. Bellina, Jr. Ph.D.
Professor of Physics
Saint Mary's College
Notre Dame, IN 46556

On Nov 11, 2008, at 3:20 PM, John Denker wrote:

I've got a question: As a matter of good pedagogy, should
we perhaps de-emphasize the whole notion of "inertia" in
favor of more specific notions and conventional scientific
terminology?

As far as I can tell, "inertia" is a non-technical term,
and there is little if anything to be gained by imposing a
technical meaning on it.
The /word/ appears in some technical terms, such as
"moment of inertia" but that is not relevant to the
present discussion.

In the Feynman Lectures on Physics, the term "inertia" appears
once as a phenomenon and once as a physical quantity:
-- As a phenomenon, "inertia" is synonymous with Newton's
first law of motion. Volume I page 2-3.
-- As a physical quantity, "inertia" is synonymous with
mass. Volume I page 7-11.

So my question is, in a technical context, if you mean the
first law of motion, why not just say "the first law of
motion"? Or if you mean mass, why not just say "mass"?

Of course in a non-technical context, it's perfectly OK
to use non-technical terms.

Also, I'm not allergic to /mentioning/ a non-technical term
... provided it is merely mentioned and not emphasized.

This whole thread worries me, because it seems to give too
much emphasis to "inertia". It seems to delve into fine
points that were never worth delving into.

=====

The same pedagogical point arises in connection with other
terms:
Example: "blue" is a qualitative term. It is not worth
delving into the fine points of "blue", because if you
were trying to be quantitative you would use other terms
and other concepts, such as wavelength.
Example: "heat" is not easy to define in a useful way. It
is not worth starting a holy war over the definition of
"heat", because if you were trying to be quantitative you
would use other terms and other concepts, such as energy,
entropy, and/or temperature.