Re: When Physical Intuition Fails

[Brian Whatcott <betwys@DIRECTVINTERNET.COM>]

At 11:42 PM 10/29/02, John Mallinckrodt, you wrote:
> /snip/
> I think you may be confusing two different meanings of the word
> "elastic."  The sense of the word that is relevant to the current
> discussion is "nondissipative."  I suspect you may be using the word
> in a mechanical engineering or materials science context, one in
> which it means "nonpermanently deforming."  That sense of the word is
> not, however, particularly relevant to this discussion.
>
> >When I visualize a mass suddenly hung onto a steel strip,
> >I see a fully elastic extension of the strip's length. Do you?
>
> I don't, but I can see how you might.

/snip/

> John Mallinckrodt


I am perceptibly at the point of diminishing returns with this
particular puzzle.
I will merely mention for John's sake, that when he demonstrates
 an elementary  differential equation of dynamics, it is a mass on
a spring that he uses.
And the spring constitutes a steel strip wound into a coil, heat treated
and tempered appropriately.

And yes: the mass bobs repeatedly, until the damping effect of the air
(principally) damps the motion.   He will remember that he models the
 damping as velocity dependent  in recognition of this air turbulence
dissipation. Just because one does not see this always present elastic
stretching in a stiff engineering member does not mean it is absent.

Or perhaps, a more vivid illustration: when you look along the wing of
the next plane you fly, consider the major deflections as turbulence
 is encountered.


Brian Whatcott
  Altus OK                      Eureka!

This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.