Re: [Phys-L] inertia ... or not

[Chuck Britton <cvbritton@embarqmail.com>]

This may be relevant or not.
Many Pedagogues point out that Newton's First Law is unnecessary 
because it is a special case of the Second Law. Therefore - 
simplicity sez - forget the First Law of Motion.

I say - BS. The First Law (often called the Law of Inertia) was and 
IS the significant break with Aristotelian thoughts of Motion. If you 
think that modern society has moved beyond the ancient Aristotelian 
ideas - you've never administered the FCI or asked similar questions 
of your intro students.

And - by the way - the word 'tend' has no place in Newton's First Law 
of Motion in spite of current TV ads to the contrary.

	A moving object WILL remain in motion . . . . . .
	An object at rest WILL remain at rest . . . . .

	until that outside influence is brought to bear.

If you want to advocate doing away with the word inertia - fine - but 
PLEASE don't do away with Newton's First Law of Motion.

Yes, I know, we're not supposed to think about Physics historically - 
but SOMEhow we've got to come to grips with the Aristotelian mindset 
in order to move beyond it.

;-)
.
At 2:58 PM -0700 5/31/12, John Denker wrote:
> Hi --
>
> I have noticed some introductory physics books like to introduce
> the concept of /inertia/ ... and then define mass in terms of inertia.
>
> In contrast, there are plenty of highly respected physics books
> that define mass directly, without mentioning inertia.
>
> Maybe I'm missing something, but I have to ask:  Why would anybody
> bother introducing the concept of inertia?  Why not cut to the chase?
> Why not take whatever process is being used to define inertia and
> use it to define mass directly?
>
> > From a tactical and pedagogical point of view, it seems like a waste
> of effort to define two concepts when only one is needed.
>
> > From a technical point of view, I'm not even convinced that the
> vernacular notion of "inertia" corresponds all that closely to
> mass;  I suspect many students (and many adults), if they thought
> about it at all, would say that a fast-moving car has "more inertia"
> than a slow-moving car, as manifested by the fact that it is harder
> to steer it around a sharp corner.
>
> So this brings us back to the pedagogical principle that learning
> proceeds from the known to the unknown:  You can't define mass in
> terms of inertia unless the students already have a reliable notion
> of what inertia is ... which they almost certainly don't.  They might
> have no idea, or they might have wrong ideas.
>
> I leave it as a question:  Is there any scenario in which it makes
> sense to introduce the concept of "inertia" in the introductory class?
>
> ========================
>
> If this comes down to another case of "we have to cover it because
> it's in the state-mandated standards" I'm going to tear my hair out.
>
> I quote from  http://www.p12.nysed.gov/ciai/mst/pub/mststa4.pdf
>
> >  * explain and predict different patterns of motion of
> >  objects (e.g., linear and angular motion, velocity and
> >  acceleration, momentum and inertia).
>
> No mention of mass ... just inertia.  Aaaarrrrrgggghhhh!!!!!
>
> These asinine standards and tests defeat the purpose of having an
> educational system.  This has got to stop.
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