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

["Rauber, Joel" <Joel.Rauber@SDSTATE.EDU>]

Amen!

Of course, many of our demonstrations have the same problem that Aristotle had, how do you get rid of resistive/dissipative forces in a demo environment? I'm sure many of you have some clever ways and demos that convincingly demonstrate the point John Clement is making.  Or do you?

Joel

_________________________

Joel Rauber, Ph.D 
Professor and Head of Physics
Department of Physics
South Dakota State University
Brookings, SD 57007
Joel.Rauber@sdstate.edu 
605.688.5428 (w)
605.688.5878 (fax) 

"Not everything that counts can be counted, and not everything that can be counted counts"
A. Einstein


> -----Original Message-----
> From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
> bounces@carnot.physics.buffalo.edu] On Behalf Of John Clement
> Sent: Wednesday, September 29, 2010 1:50 PM
> To: 'Forum for Physics Educators'
> Subject: Re: [Phys-l] [PTSOS] anvil and sledgehammer inertia demo
>
> 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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