Re: cause of loud noise from brown paper bags

I do not think it is the bending of the paper that causes the sound. If you bend 
a small piece of the bag, it does not make a very impressive sound. Rather it is 
probably the surfaces of the bag that are being moved quickly into different 
positions that creates the sounds. Try snapping your finger against the side of 
the bag. You will get a much more impressive sound.

Sound is just moving air and the sides of the bag are moving the air. Each small 
segment of bag is acting like a small loudspeaker. The stiffness of the bag  
allows "creation" of many small segments which "snap", "crackle", and "pop" back 
and forth rapidly as the bag is being distorted into a smaller space. 
Loudspeaker cones used to be made of paper (some undoubtedly still are ), and 
the magnetic voice coil moved them rapidly back and forth to make sounds, 
sometimes very loud ones.

Hope this helps,
David Winsemius, MD