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



John!

I think, after reading the first google match, that Brian's reference is to the bag's crackling when opened and when flexed by reaching in to get a chip. The effect is similar, I presume, to very dry kraft paper.

"Besides the fact that they suck (especially the garden flavor) don’t open a bag after a few nips of your favorite whiskey after the wifey is asleep.
LOL! This is exactly what prompted my post :) My wife was asleep upstairs and I opened the bag in the kitchen and it literally woke her up. Man that bag is loud!

Harvest Cheddar is pretty good IMHO. Of course, all the neighbors will know you're eating them :)


http://www.freerepublic.com/focus/chat/2408461/posts


bc knows if it's a low humidity day when he folds his shopping bags


On 2010, May 29, , at 18:01, John Denker wrote:

On 05/29/2010 04:53 PM, Brian Blais wrote:
Anyway, I thought there might be some interesting physics activity in
there somewhere, but I am not sure what.

There is some interesting and fairly complicated physics involved.

At the phenomenological level, there are various ways something
can respond when overstressed. At the extremes we have:
-- plastic deformation and creep, versus
-- brittle fracture.

And then there are all shades of gray in between. Famously
Silli-Putty (silly putty?) will creep if stress is applied
slowly, but it will shatter if shocked:
http://plc.cwru.edu/tutorial/enhanced/files/polymers/therm/therm.htm
http://www.youtube.com/watch?v=uWYxc8xhihg

Ideal crystals tend to be brittle. That is, once a crack is
formed, it tends to propagate like crazy. This can be understood
in terms of the Bragg-Nye model. Feynman has a chapter on this.

To make a loud bag, you need
a) strength, obviously, and
b) brittle fracture (not plastic creep so it "lets go" all
at once.

OK?
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