Re: [Phys-l] [PTSOS] anvil and sledgehammer inertia demo

[Bernard Cleyet <bernardcleyet@redshift.com>]

Paul!

I did not write that;  I quoted someone who did.  [Furthermore, not only are you miss quoting,** I thought it was understood that I disagreed with that by my statement that such demos. were (unfortunately) necessary, but only to grab their attention.  As JC pointed out, that property of inertia is common knowledge -- What is not common is motion continues w/ balance forces.  (Contrary to Aristotle!)

The discussion on phys-l has continued (20 total so far) and is now concentrating on how to show, inter alia, instead of tail chasing, the forces are equal, but there is motion.

Regarding separating area and inertia.  A very simple one, and half gee whiz, is the weight suspended by a thread.  hanging from the bottom of the weight is another thread (same strength). If one pulls w/ gradually increasing force the upper one breaks, if jerked the lower.  This is an old one, so not surprised if PTSOSs know it.


Of course there's more to teaching than ...  But content and pedagogy is essential.   Which reminds me, how many of you use the FCI?

Force Concept Inventory

** His quote that I quoted is:



On 2010, Sep 29, , at 11:49, John Clement wrote:

> Beyond that most inertia demos just show that an object at rest remains at
> rest.  Everyone including Aristotle knew that.  That type of demo is simply
> not worth doing.  The really important demo is to show that a moving object
> with balanced forces remains in constant motion.  That is what students
> don't believe.  Showing that an object remains at rest when forces are
> balanced is also not worth doing.
>
> If you ask what unbalanced forces do students will say make things move.  If
> you probe more deeply they mean move with a constant speed.  So getting them
> past this idea is important, and the traditional inertial demos are not
> worth the hammer to pound them with.
>
> And of course before doing the balanced forces produces constant motion demo
> students need to predict what they will see.  They need to commit to what
> they believe so the correct answer will replace it via reconsolidation.
>
> John M. Clement
> Houston, TX

bc

On 2010, Sep 29, , at 21:41, Robinson Paul wrote:

> I'm sorry, but I disagree with the notion that demonstrations are not worth doing. Lots of things we as physics teachers do are accomplishing more than being heuristic or good pedagogy. Often times it is difficult or impossible to isolate just one variable. 
>
> For example, there is more to the dishes on the table-coth demo than inertia--impulse and momentum, friction, are also involved. Many new teachers--even veterans--are not aware of such subtleties. But that doesn't mean we shouldn't do it. Done properly, it is a memorable demonstration that students will impress students for a lifetime.
>
> There is more to teaching than content and pedagogy.
>
> Go Giants!
>
> Paul Robinson
> Physics Teacher
> San Mateo High School
> 506 N. Delaware Street
> San Mateo, CA 94401
>
> (650) 400-9425, cell
> (650) 369-1220, fax
> pablo@laserpablo.com
> www.laserpablo.com
>
> On Sep 29, 2010, at 3:12 PM, Bernard Cleyet wrote:
>
> > > Showing that an object remains at rest when forces are
> > > balanced is also not worth doing.
>
> __._,_.___
>
>  
> __,_._,___