[MeganM (OP)]

Ema wants to know:

Why, and especially how, does paper (or any material) make sounds when crumpled? Where does the differences in sound for different materials come from?

Thoughts?

[evan_au]

In university we studied the sine-wave frequency of a plucked 1-dimensional string (on, say, a guitar).
- A crumpled surface consists of many 2-dimensional surfaces, so the result will be more like a drum than a string (and the sine waves will become more like Bessel functions), but I am sure that many of the same parameters apply...

The velocity of waves in the material, which in turn depends on the tension and the density
The dimensions (width & height) of each little facet of the crumpled sheet
Deformations caused by the crumpling
The energy losses in the material (high in paper, low in aluminium foil)
Plus coupling into adjacent facets

See: https://en.wikipedia.org/wiki/String_vibration
https://commons.wikimedia.org/wiki/Category:Drum_vibration_animations

[Nakoyasen]

This is a forum. Knowledge Store I do not know where to find it.

[weilein]

Thank you so much for the solution.

[Awlaki]

the article very good and 1 also very useful for me

[jrjong]

Ema wants to know:

Why, and especially how, does paper (or any material) make sounds when crumpled? Where does the differences in sound for different materials come from?

Thoughts?

That's pretty interesting. Never thought of the paper sound on this way. And thanks evan for the links. Will definately look into it. Nice observation though.

[sciencefreak24]

Based on my own personal observations, it looks like it's caused by a process called snap-through-buckling. Doesn't look like Wikipedia has a decent explanation, so I'll try my best.

Snap-through-buckling is a process where a material deforms under a non-linear stress-strain curve. The best example is on your keyboard. If you have a modern keyboard, then you can feel snap-through-buckling for yourself. Notice how your keys don't really feel like just a spring on a button. It "clicks". That's because the series of springs under each key is designed to apply a different amount of force depending on how much you press down. The force will increase as you press down, but there's a point at which the applied force dips and causes you to fall through.

This similar behavior can be found on the tops of Snapple bottles. There's a little "button" on top that you can kinda click. It's supposed provide an indication about the internal pressure in the Snapple bottle. If it's too high, the cap will pop as opposed to gradually rising directly proportionally to the internal pressure. That's because of snap through buckling.

Now, my theory is that when you crumple paper, you create a bunch of 2-d planes that are unevenly folded in 3-d space. By applying additional force, some of these 2-d planes will pop open, like in snap through buckling.

When your paper gets wet and you let it dry, the water restructures the wood pulp that composes the paper making what would otherwise be a 2-d plane into an uneven 3-d surface.

Hope this helped!

[ammocave]

If you break a piece of wood, it will make a noise as you break a lot of chemical bonds in the wood, releasing unnecessary energy in the form of sound and a small amount of heat. The structure of the paper is quite similar, with the exception of grinding, so it makes a noise, and you tear the same cellulose strands.

[Bored chemist]

If you break a piece of wood, it will make a noise as you break a lot of chemical bonds in the wood, releasing unnecessary energy in the form of sound and a small amount of heat. The structure of the paper is quite similar, with the exception of grinding, so it makes a noise, and you tear the same cellulose strands.

But, if I crumple a piece of paper and then opent it out again, it's not broken. It's still a piece of paper.

[evan_au]

if I crumple a piece of paper and then open it out again, it's not broken. It's still a piece of paper.

(presumably, in contrast with the shattered stump of a tree? And contrasting the crinkle of crumpled paper with the creak and crack of a broken tree trunk?)

Most of the bonds in paper fibers were shattered long before we end up with the paper, during:
- Cutting down the tree (which starts with long, parallel fibers, strongly bound together)
- Woodchipping the tree (producing short lengths of parallel fibers)
- Chemically and mechanically separating the individual fibers into a slurry (mixed with binders like clay)
- Leaving the short, separated fibers to settle in random directions before drying.
- These fibers are not strongly bound to each other.

Individual fibers of small diameter have a smaller bend radius than a solid block like a tree trunk, so you can bend paper more sharply than you can bend a tree without catastrophic failure....
See: https://en.wikipedia.org/wiki/Papermaking

By the way, I heard an explanation of why you can use paper for origami, but not aluminium foil:
- When you bend paper, it breaks some fibers, and loosens others from the binder. So when you bend that region of paper again, it is likely to fold in exactly the same place.
- When you bend aluminium foil, it work-hardens. So when you bend that region of the foil again, it will bend somewhere else (ie somewhere that has not been work-hardened).