What Makes Plastic Noisey??

I want to know why it only makes a noise when I am there to hear it?

Hello Electroman! I suppose it just your ferret pet does plastic bag noisy as well as mine dog pet likes do the same with plastic bottle !

To be more seriously, I think it is set of physical properties of plastic (stiffness factor/Young module, viscosity and etc). Plastic is artifical material and as any human-made material it was pursued some profitable purposes due to its design. Plastic media for bag should be light, hermetic, safe for storing meal and etc. So it seems the noisyless had not been taken in account ever as key designing criteria.

So noisy is side effect that is so adorable by ours pets.

Imagine a glass in moment it's broken up. It makes good noise for a short time than glass gragments are believed to be more silencer. So i draw the analogy that plastic is like glass that we can't break completely owing to its predesigned structure.

Plastic is fragile and non-fragile for the same time, viscous and non-viscous.

But plastic porous media structured with micro air bubbles make it not so transparent for acoucstic waves and therefore quieter.

Best regards to you and your ferret.

Hello caramba! I don't know why are pets love the noise, but I would guess that the noise extends to very high frequencies above our hearing but still within our pets hearing range?

Some one somewhere must have done some work on this problem / ability of plastics?

John.

Many more explanations regarding plastic but less regarding the pleasure to create noise ... is it that our pets by creating noise they feel the same way as we, humans, do, when we create music?

Mine was one of the votes against this being OT - I feel this is an extremely valid point. If the ferrets, dogs, cats, etc. of the world did not enjoy making the noises, there would have been no reason to ask the original question!

The noise is the result two things:

1. physical vibrations from the plastic changing its shape.

The plastic is composed of very long molecules. When bent, it will snap into a new shape in an attempt to equalize or minimize the pressures. The stiffer or more dense the material will create more noise. High density polyethylene (HDPE) plastic will make more noise then Low Density polyethylene (LDPE) plastic. To have vibrations, you must have a resonant frequency or fixed length of a certain area in the plastic. The softer more pliable plastic has more varying sized areas. This results in less surface pressure, different frequency and lower power vibrations.

A good comparison of how a stiff plastic reacts would be to lightly dent a pop can and let it pop out. The plastic has the same physical action on a smaller scale but multiplied in quantity.

2. Breaking of molecular bonds.

When plastic is crinkled or crushed in a ball, a few of the molecular bonds are broken.

A good comparison is to take a small green stick and bend it until you hear snapping. Some of the strands are broken yet the stick remains relatively whole with a weak spot. You can re-bend this stick many times before all the strands break.

The same thing happens with the plastic, however, being more flexible, it will withstand many bends and breaks. The plastic that no longer makes allot of sound has many small breaks.

Hmmmm okay, but how do the breaking molecules create a noise?

Is it simply made by the molecular link pulling apart and if so I guess that would be why the noiseyness factor reduces with age and number of crumples...

I suppose it could be the same as your analogy of a breaking twig or a glass reinforced plastic where each breaking bond causes a sound but it still leaves the whole as one unit but weakened...

But what makes a noisier plastic bag more noisey than a quieter one?

John.

As the molecules are stretched to the limit and break, the two parts snap back to an un-stretched condition and vibrate longitudinally.

The noisier plastic bags are usually HDPE bags. The quieter ones are LDPE. It is the higher density, stiffness, and potential energy that makes the difference.

Also thickness will make a difference.

What will make more noise; Aluminum foil or an aluminum can?

Yes, point taken Techno...

I suppose its the notion that many years ago I think I read an article that said it was to do, possibly, with piezo action inside the material or something, not sure now!!?

"piezo action " I think that is stretching it a bit far!

Although Piezo action uses the elasticity of materials combined with electricity to create vibrations, I don't think the noise in plastic has anything to do with electricity inducing vibrations.

Techno, I was thinking of two articles, one was about the fact that very low levels of light emissions had been observed from a plastic material when it flexed, that led to the statement that they researched it and explained it by the piezo effect.

Maybe long plastic molecules breaking could develop a static charge?

John.

I recall years ago seeing video (and replicating it in real life) of 'sparks', or light flashes given off by chewing on candies (Mentos? don't recall) which was attributed to a pizeo- (or similar) electric effect from bonds between sugar molecules breaking. Plastic bags made from cellulosic materials (corn cobs, etc.) might have similar carbohydrate molecule bonding. Doubt it would create sonic waves, but no proof either way yet.

I turned the lights off in the shed and chewed on a plastic bag. Nothing. Very disappointing.

Now I have the blank stare of a very puzzled She questioning my sanity.

Yes, and no

The breaking of bonds will create light, electricity etc. However the true definition of piezo is to add electricity to create vibrations.

The action of breaking a bond is like this;

You add physical energy to the bond and atoms by stretching it. The energy and vibrations builds up until it can no longer keep its form. The bond breaks and gives off excess energy.

The excess energy can be in many forms:

1. heat
2. light
3. electrons (electricity)
4. Large atomic particles Particles
5. molecular particles.

The electricity is a result of the break, not the cause. The cause was a build up of energy from a physical force.

Must be a hellofa molecule to make that much noise when it breaks.

But what makes a noisier plastic bag more noisey than a quieter one?

I wouldn't agree with this statement for any non-restricted time. But for relatively short time span (till your ferret will be bored this game) I would agree that plastic material can generate stable level of noise even increasing one for a some time, but it'll come to its quieter state after all when all potential energy will have been spent.

What is a noise? From common viewpoint it's somewhat as unpleasant sound. Ok, what does make sound unpleasant? When someone touch a guitar string it makes sound just called as harmonic thought to be pleasant for hearing. But when we're experienced of scored chaoticaly distributed strings' sounds it converts to noise.

Let's consider four items glass, triplex glass, plastic bottle. All items are exposed endless series of kicks.

Initially every item is described consists initially no matter one solid spot, membrane or string

m*d^x/dt^2+beta*dx/dt+cx=0; (1)

f=1/2pi*sqrt(c/m) --- frequency;

A(beta)- average build up sum of absolete magnitude of harmonic oscillation for string during 3-4 tau.

W=A*f=const --- energy factor of system.

After first and last kick for glass we get significant A for a short time from some oscillating fragments. We get a few fragments every one makes its contribution in summary level of noise. Then we get silence as heap of glass fragments can't generate significant noise. W=const.

For triplex glass we need to get some kicks and get more fragments. Every new fragment is getting smaller has more frequency and less average magnitude. But W remaims the same.

For pl bottle we get prolonged process of creation new membrane clasters. First jammings of my dog pet used to be very loudy as he fight with not only bottle elastic property but (as techno said exactly with its cylindric shape and thickness to compare a pl bag). Then process looks with rosen noise level as though new membranes can generate less level but it's number and summary square exceed sum square of gashed boundaries. Bottle loses its shape and transparency covered by crackles. Then when we get situation when of momentum. After all most surface of former bottle is covered non-elastic boundries than membranes capable to generate any significant sound and my pet demands new toy for his game.

For pl bag we have similary situation but only significantly increased duration of growing up noise and its stabilazing. But all shall be stay still no mater how long time we are ready to listen playgame of ours pets.

I do not pretend my explanation are correct, it's not even theory but very simple model.

Kind regards to everybody.

Vlad.

P.S. Take a look on fig.

"m*d^x/dt^2+beta*dx/dt+cx=0" - hmm...

Is that m * (d^x/dt²) + β * (dx/dt) + c * x = 0, or what?

Don't make much sense to me .

m - mass of ocassiaonally created membrane;

beta- viscousity coef;

c- elastisity factor.

It's classic expression. I've meant there had been appearing a lot of such membranes that create something like a "white noise". At initial moment suddenly changed boundry conditions can be considered as applied force like delta-function. So we have contrary going process creating of sounding membranes (elastic zones) and it's boundries (viscous zones).

Don't much sense for me why don't you log in Guest? Your remarks are to the point.

Shouldn't it be:

"m*dx^2/dt^2+beta*dx/dt+cx=0"

i.e.

m * (dx²/dt²) + β * (dx/dt) + c * x = 0 ?

Yes, Guest, thanks. I've not properly working editor script in my browser.

m*dx^2/dt^2+beta*dx/dt+cx=0

m * (dx²/dt²) + β * (dx/dt) + c * x = 0

These are 2 very different equations.

These are the same, but written in different notations. Opps! I'd noticed small mistake, it shoud be wrtitten m*d^2x/dt^2 for first memeber, but it's not a great sense.

sorry for my Opera brows doesn't permit me use script editor

Kind Regards

So m(d²x/dt²) + β(dx/dt) + cx = 0

- is that your final answer?

Yes, sure. Thank you. Have you understood my approach a whole? I so sorry for my poor language.

'Scuse me for letting my ignorance show, but what have your graphs got to do with the differential equation?

It's nothing, your ignorance. I thought and believe that all participants of cr4 forums (guests include) have very very good knoweledges and experience to extrapolate diff eqs to plausible graphs outputs. And there are some hmm.. restrictions how much should be written in modest forum window. Ok I think about and will write you maximum short one of probable developing of idea tonight (my time zone) if you wish. Best regards.

Simple two-dimension model.String (membrane) has initial length L. ρ-linear density kg/m.

1st step. Let us to suppose there is tiny cannon that can shoot the membrane. W(i) - kinetic energy of impact; i- iteration step; W_th - threshold for creation non-elastic zone. Shooted place with coordinate z₁ splits membrane on two parts with length L_i1 L_i2 and makes there non-elastic zone ΔL.

Therefore L_i1+L_i2 < L.

W,z1 --- can be obtained as random generator output.

2nd step. We get two oscillators described its ODEs and it's easy to resolve its.Initially oscillators are subjected force impulse (neliglible small) and as the main factor in no time changed parametres of mech systems, m1,m2. Therefore we should resolve here two ODEs for given initial conditions and new parametres of system.Third step. Next shoot. Get W of shoting and z.

If ( z1(i+1) == z1(i) ) i.e.if we've shooted to old non-elastic zone there nothing happens new.

If ( z1(i+1)!=z1(i) && W<Wth ): we can't create non elastic zone but only renew already some faded oscillation at existing zone.

If ( x1(i+1) != x(i) && Ws>=Wth ) we get new membrane splitting and one more membrane as well as one more non-elastic zone ΔL.

4th step. Loop to step 3. We can launch simultaneously resolving for a set of such membranes getting produced more real sound.

Needless to say that for every step we should resolve ODEs for given parametres and initial conditions. Oscillating graphs can be stored in file as summary superposition that can be further processed through sound system. It can be easy realized by means of any language (Basic, Pascal, C) or math software Matlab, Scilab, Octave.

Gradually when ΔL will stay comparable with L we won't get significant sound level at output.

Algorithm should be applied simultaneously for a several of such membranes. Parameters and initial conditions can be adjusted.

I emphasize it's only model. I can't insist it's correct, but I bet it can be realized and produce a sound so far from Mozart sym#40. Therefore shown above graphs at least have a sense. For glass we have only first two steps. It's possible to make 3-d decision with PDEs as well.

Best regards, Guest.

This is a logical approach, and while I have not taken sufficient time to fully analyze the math, it 'looks' right. My feeling is that each 'crinkle' is amplified by the plane of non-crinkled material around it, and as the uncrinkled zones get smaller and fewer, the sound level dies off.

Much is dependent on the nature of the plastic itself. Old-fashioned cellophane is relatively stiff and durable, thus louder for longer than more modern polyethlylenes, vinyls, styrenes, etc. that can also be used for thin films such as bags. These tend to be softer and/or crumple without rebound more quickly.

Yes it's just model and it does represent non-original iterated logic calculations. I can't get all nuances of English but in Ru the model and the theory both are very different notions. For instance Ptolemy's Geocentric model of Universe was absolutely wrong but it was pretty workable for ancient navigation issues. So as mine one very abstract, very simplified, but it can work for understanding the matter. I hope.

As for cellophane and other material, I share your viewpoint --- all depends of set of its properties both geometric and physical ones. I very doubt ours ears can hear broken moleculas at edges of pieces of broken sword, but propagation of waves along broken steel surface -- why not?

Best regards.

I'm with you on that. Hearing molecular bonds break is something Spiderman (the cartoon superhero) might be able to do, but I'm doing good to hear the vibrations along the metal surface of the bell on my alarm clock in the morning! Sword edge molecules shearing - I don't think so. Surface vibrations along the blade - MUCH more likely. Same goes for plastic films. The stiffer the film, the louder the crunch.

Just as a speaker moves in and out creating a sound wave the surface of the plastic does all so. As the plastic is moved small spots flex back in to shape from the memory in its extrusion. After flexing a while it starts to be more supple loosing some of the memory.

I think the 'clicking frog' effect probably has a lot to do with it. The material flexing between two stable states due to the multiple folds. The transition between states is rapid and thus generates a sound pressure front (and presumable back as well..damn, I've gone silly again)

Del

Plastic bags seem to be made of a very stiff material in a very thin sheet. As the bag is put into use, creases are formed in the bag.

Could it be that the noise comes from the formation of folds and creases in the plastic much like what you hear when you crumple aluminum foil. The noise diminishes over time as the accumulated folds make the bag more flexible. In effect, the bag becomes broken in and is no longer as interesting.

Another source of sound is the bag material rubbing together as is is folded and compressed. The wrinkles and folds of the plastic bag vibrate and produce sound when they are crumpled together. Once again, as the bag becomes broken in, the volume of sound diminishes.

Soooooo on the one hand we have Techno and others saying its the plastic molecular chains breaking, which I would assume is irreversible? and thus the plastic eventually loses its noiseyness.... But somehow it remains in one piece?

On the other hand as Del and others said it could just be the flexing of the plastic from one shape to another, which I suppose does explain why when you crumple a bag and let it sit undisturbed it contiues to crackle as it trys to return to its original shape?

Hmmmm maybe its a combination of both?

John.

While the analysis as to why plastic makes noise, and that it diminishes over time has been fantastic, I am surprised that no one has mentioned that it is better to avoid taking the plastic bag and, instead, bring a reusable cloth bag to the store. Your ferrets may suffer, but the planet they live on will be better off.

In the alternative, don't always take the bag offered. Why do baggers put milk bottles with handles in a bag? Why do we need a bag for an item that fits in a coat or pants pocket? Of course, we don't. Also, if the bagger does bag an item, and you tell them you don't need a bag, make sure to tell them to re-use the bag. Many times, they will take your item out of the bag, and then toss it, as if it was somehow unfit for use again.

"Why do baggers put milk bottles with handles in a bag?" Cos my hands get cold.

"Why do we need a bag for an item that fits in a coat or pants pocket?" We don't if we've got big enough pockets. Are you, by any chance, a poacher? Time was, you could get hanged for that (if you were lucky) - or even transported to Oz!

Just a a visual representation, could you use corrigated cardboard and break perpendicular to the internal ridges to act as a comparison in justifyable magnitude as to what is taking place?

If so then I agree with the hypothesis of the molecular breakage theory.

For the case of paper bending or tearing it's not the fibers / molecules that break, but the hydrogen bonds between the fibers / molecules in the formed shape. Could this be true in plastics as well? My cat is scared of crinkly paper bags!

I don't have a ferret to experiment with, and I'm not a vet, but here's my guess ; Ferrets like to wriggle about in tight holes. The passing of flaired trousers was coincident with the introduction of plastic bags. Being inquisative, the ferrets were bound to experiment with the bag alternative, and there they discovered the joys of static. The majority of plastic bags don't contain air holes, and so the ferrets then discovered the perverse pleasure of auto-erotic asphyxia. Is the ferret panting when it emerges ? Is it blue/flushed in the face ? Thought so. The observed reduction in noise after a while is simply 'recovery time' which varies from ferret to ferret. I suggest that you shave your ferret and feed it bromide with utmost urgency.