Re: [Phys-l] loud bag...physics?

[Brian Whatcott <betwys1@sbcglobal.net>]

Brian Blais wrote:
> Hello,
>
> Not sure if this is an interesting physics question, or just a  
> curiosity, but has anyone seen the new Sun Chips biodegradable chips  
> bag?  It is LOUD!  Compared to any other plastic-type bag, it is  
> astonishingly loud, and I was wondering which properties of a bag  
> affect the loudness.  Since it is biodegradable, it isn't made of the  
> same stuff, but if feels mostly the same (perhaps a bit stiffer).
>
> Anyway, I thought there might be some interesting physics activity in  
> there somewhere, but I am not sure what.  If not, at least it is  
> curious.  (you can google loud sun chips bag and get a lot of hits,  
> including a description of the bag itself).
>
> 					bb
>
>   
It is a sadness of composite materials, that when they reach their limit,
they fly apart - sometimes in an explosive hail of dust.
When structural steels and aluminum alloys reach their limit, they
yield, and if the excess load is  not too high,  return from the
exceedance with a permanent bend or stretch.

  It was for this reason that early fiberglass sailboat hulls were thick,
almost as thick as the wooden hulls they replaced. (Just as Ironbridge
over  the Severn, the first iron bridge, looks very much like a wooden
trestle/arch upon which it was modeled.) Those early hulls are still
around, spoiled only by the rotting plywood floors or stringers with which
they were furnished.
Plastics in general, have a plastic stage after the elastic deflection 
range is
exhausted.   I expect that if you cut a thin strip of this bio 
degradable material
and mark it at intervals, that it would still show much the same length 
after you
stretched it to failure. A regular plastic strip should show some extension
in that situation.

Brian W