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

["John Clement" <clement@hal-pc.org>]

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

> Those, below, contrary to the subject are not inertia demonstrations, but
> pressure ones.  Cf. spike heels or track shoes and snow shoes.  I on
> rereading understand David and likely Dennis understood this, so my
> comment changes to:  Illustrating two effects in one demo. is likely not
> heuristic, or good pedagogy.
>
>
>
> bc recalls the sign at the entrance of the cork floored auditorium at the
> Stoke on Trent College of Further Education:  No spike heels.
>
>
> On 2010, Sep 28, , at 22:46, Dennis H wrote:
>
> > I used to use a big round of wood that I'd get each year when I cut my
> firewood. I would let the student take a big swing with the sledge hammer.
> Did this successfully for years. I never imagined that he could miss the
> round (about 1.5 ft. diameter). The sledge glance off the wood. I didn't
> get hurt that time, just scared. Now I just talk about it and show the
> video. There are too many good inertia demos to die for one that's a bit
> dicey.
> >
>
>
>
>
>
>
> On 2010, Sep 28, , at 22:36, Bernard Cleyet wrote:
>
> > Area?  Please explain?
> >
> >
> > bc
> >
> >
> >
> > On 2010, Sep 28, , at 05:29, David Geller wrote:
> >
> > > I borrow a 20 kg plate from our weight room. The only difference is
> that the large area adds to the inertia effect.
> > >
>
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