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Scientists Explain the Sound of Knuckle Cracking (bbc.com)
"The BBC reports on something sure to impress your next date -- and possibly your last -- when you explain it," writes Slashdot reader dryriver. From the report: Scientists have turned their attention to investigating that most annoying of human habits -- the sound made when you crack your knuckles. The characteristic pop can be explained by three mathematical equations, say researchers in the US and France. Their model confirms the idea that the cracking sound is due to tiny bubbles collapsing in the fluid of the joint as the pressure changes. Surprisingly, perhaps, the phenomenon has been debated for around a century. Science student Vineeth Chandran Suja was cracking his knuckles in class in France when he decided to investigate.
"The first equation describes the pressure variations inside our joint when we crack our knuckles," he told BBC News. "The second equation is a well-known equation which describes the size variations of bubbles in response to pressure variations. And the third equation that we wrote down was coupling the size variation of the bubbles to ones that produce sounds." The equations make up a complete mathematical model that describes the sound of knuckle cracking, said Chandran Suja, who is now a postgraduate student at Stanford University in California. "When we crack our knuckles we're actually pulling apart our joints," he explained. "And when we do that the pressure goes down. Bubbles appear in the fluid, which is lubricating the joint -- the synovial fluid. "During the process of knuckle cracking there are pressure variations in the joint which causes the size of the bubbles to fluctuate extremely fast, and this leads to sound, which we associate with knuckle cracking.'' The study has been published in the journal Scientific Reports.
"The first equation describes the pressure variations inside our joint when we crack our knuckles," he told BBC News. "The second equation is a well-known equation which describes the size variations of bubbles in response to pressure variations. And the third equation that we wrote down was coupling the size variation of the bubbles to ones that produce sounds." The equations make up a complete mathematical model that describes the sound of knuckle cracking, said Chandran Suja, who is now a postgraduate student at Stanford University in California. "When we crack our knuckles we're actually pulling apart our joints," he explained. "And when we do that the pressure goes down. Bubbles appear in the fluid, which is lubricating the joint -- the synovial fluid. "During the process of knuckle cracking there are pressure variations in the joint which causes the size of the bubbles to fluctuate extremely fast, and this leads to sound, which we associate with knuckle cracking.'' The study has been published in the journal Scientific Reports.
something sure to impress your next date -- and possibly your last
Not bloody likely, my last date stopped answering my calls.
Corruption is convincing someone that the selfless ideal is the same as their selfish ideal.
* Why does this uncomfortable feeling happen in the first place that goes away when you crack your knuckles?
* What causes the bubbles?
* Are the bubbles related to the feeling, or not or merely a side-effect?
And it's not just knuckles. Toes, shins, knees, elbows, neck, ... it seems it can be everything, depending on the person.
this is boring stuff.
I won't bother to look up the original reference(s).
Noted.
And this kind of "modeling" is, er, crude. Among other problems, it sorta oversimplifies the strain field in the surrounding fluid.
How do you have a "strain field" in a liquid?
Typical of would-be physicists.
Considering that you think quoting your sources is beneath you, and you seem to be using terms you don't understand, it is possible that your condescending attitude may be unjustified.
What I said is perfectly understood by any proper scientist.
First, it it those people's duty to look up the possible references, if they want to style themselves as, you know, scientists; since this is very old news, and I'm not the one at fault, I won't spend the time required to find the old papers.
Second, if you had any kind of skill in the field, you would have noted that the paper talks about "fluid", not "liquid". That's not the same thing. Learn elementary rheology, or better, continuum Mechanics. I won't start a basic course here (although I could, having taught this at PhD level), but for the record, a liquid does undergo strain; but by definition of a _liquid_, only its time rate involves dissipation. And by the way, a change with time in the strain field does very obviously necessarily occur here. Then, the behavior of a general fluid can involve the strain field proper, such as occurs in say, viscoelasticity.
Do you even know what a field is in PDEs, anyway? Or PDEs? Ever heard about Navier-Stokes? Or any kind of mathematics?
that creimer never cracked... the moose knuckle!
CROFLOLFL!!!!
I think these videos show the same principle at work (at least as I understand them). It seems to be important that the formed bubbles are vacuums (i.e. formed by pulling joints apart rather than evaporating gas) because that's what allows them to collapse.
Collapsing vacuum bubbles in a fluid:
https://www.youtube.com/watch?...
How the principle explains another real world phenomenon:
https://www.youtube.com/watch?...
I've seen numerous results of research regarding this subject at least a decade ago already drawing the same conclusions.
Never seen such an attitude. You're a disgrace, and you know it, hence the An. Coward.
I bet some of you cracked your knuckles after reading this post...
wrong sound , more like a crunch ...proof see roommates face
Most proper scientists don't actually speak condescending-douche fluently. You'll need to translate a bit, since you are clearly a native speaker.
In case you were wondering what it sounds like when an auditorium full of people crack their knuckles simultaneously, here you go: https://www.youtube.com/watch?...
And you do think ShanghaiBill is at fault. Re-read that cunt's post then shut the fuck up.
You are definitely building yourself up with hot air.
What I said is perfectly understood by any proper scientist.
Strain fields are not relevant to every scientist's field (it's more relevant to continuum mechanics just as you noted), but then by applying the term "proper" perhaps you are referring to those more properly learned scientists by some canonical reference of "science" - care to share with us filthy commoners?
First, it it those people's duty to look up the possible references, if they want to style themselves as, you know, scientists; since this is very old news, and I'm not the one at fault, I won't spend the time required to find the old papers.
Second, if you had any kind of skill in the field
How convenient of you to exclude yourself from your own rules.
you would have noted that the paper talks about "fluid", not "liquid". That's not the same thing. Learn elementary rheology, or better, continuum Mechanics. I won't start a basic course here (although I could, having taught this at PhD level), but for the record, a liquid does undergo strain; but by definition of a _liquid_, only its time rate involves dissipation. And by the way, a change with time in the strain field does very obviously necessarily occur here. Then, the behavior of a general fluid can involve the strain field proper, such as occurs in say, viscoelasticity.
Do you even know what a field is in PDEs, anyway? Or PDEs? Ever heard about Navier-Stokes? Or any kind of mathematics?
You are saying all the right things as far as tooting your knowledge of fluid dynamics (at least as far as name dropping can get you), but in all the wrong ways. I assure you, you could not have taught this at PhD level, and you will probably never understand why. My guess is you are an undergrad with second order ignorance.
First, it it those people's duty to look up the possible references, if they want to style themselves as, you know, scientists;
No. Sorry, but no. You make a claim, you have the burden of proof.
I've seen people trying to reverse the burden of proof (i.e. "I claim and if you don't believe me, prove me wrong"), but asking people to prove your statement if they want to believe it, that's ... new.
We used to have a Bill of Rights. Now, with the rights gone, all we have left is the bill.
Fed up or not, the second you start to act like an a-hole when posting then other people stop caring about what you have to say, regardless of it's accuracy.
It's interesting to see that so far, I've been the only one actually saying anything specific wrt the science involved. Beyond posturing, would _you_ be able to write anything relevant to the scientific problem at hand?
> Strain fields are not relevant to every scientist's field
I was of course referring to the general problem of "scientists" not fulfilling their due diligence duty by looking for prior art. In these times of easy googling it's all the more damning.
> How convenient of you to exclude yourself from your own rules.
Huh? This is Slashdot, mate, not a formal academic assignment. Do you really expect me to spend time rummaging through old cardboard boxes?
> you could not have taught this at PhD level
Pathetic. I did precisely that about 25 years ago, for PhD students in Mathematics. Remember, I'm still the only one writing anything specific to mechanical models here. Care to show your skills by, say, telling us a thing or two about, say, properly dealing with the incompressibility constraint in CFD?
Flat out wrong. The burden of proof is obviously on the people who publish their "discovery" to show that they did their homework in the first place. And the fact is, they didn't, both because they haven't searched for prior art (I'm not the only one here stating that this study has already been done, btw) and because they do not seem to bother checking that they have the relevant skills (in fluid mechanics or rheology, at least, and possibly acoustics as well) to begin with.
And you do think ShanghaiBill is at fault.
No. In fact, considering your consistent belligerent attitude it was downright polite of him to even say your attitude "may be unjustified" instead of "is unjustified". You are at fault. Shut the fuck up.
Scientists have turned their attention to investigating that most annoying of human habits -- the sound made when you crack your knuckles
It annoys the crap out of me when the media talks about "scientists" as if they are some sort of monolithic entity. WHICH SCIENTISTS are they talking about? What are their names and specialties?
Anyway this sounds like a candidate for an IgNobel prize if I ever heard one.
> you could not have taught this at PhD level Pathetic. I did precisely that about 25 years ago, for PhD students in Mathematics. Remember, I'm still the only one writing anything specific to mechanical models here. Care to show your skills by, say, telling us a thing or two about, say, properly dealing with the incompressibility constraint in CFD?
As I suspected, you have completely missed why everyone here has issue with you: your current attitude is not welcome in the scientific or academic world because it is self serving, you may or may not have filled the role of a professor but you did not and clearly currently cannot _play_ it to anyone else's benefit. People will be interested in what you have to bring to a discussion when you stop trying to measure the length of your penis and compare it to everyone. You are not necessarily unique in this aspect, it's just that most people grow out of it, you appear to have much growing to do.
When someone says, "Any fool can see
The entire thread replying to the first comment posted here seems to be ignoring the content of that comment: this is not new. Some of the detailed analysis might or might not be new, but the main result is known.
Here are some popular articles from years back:
https://www.telegraph.co.uk/news/science/science-news/11539913/Why-knuckle-cracking-makes-a-popping-sound-and-why-it-might-be-beneficial.html : Quote: "When muscle joints are pulled apart there forms a tiny cavity filled with gas which then collapses, creating a popping noise."
https://health.howstuffworks.com/human-body/systems/musculoskeletal/question437.htm
https://articles.mercola.com/sites/articles/archive/2014/11/08/cracking-knuckles-harmful.aspx
> your current attitude is not welcome in the scientific or academic world
As opposed to well-behaved ignoramuses or even crooks who make a living out of false or nonsensical science, in many cases with taxpayers' money? How am I supposed to put up with them? Be nice, clap hands each time I've heard one lecture too many on a topic the lecturer has not contributed a whit to? And knowing that (s)he teaches the nonsense to unsuspecting students?
BTW: I'm not claiming this is true of all scientific fields; I can only judge mine, but there the camel's back was broken long ago. Just look at the sheer number of journals and papers, wonder at the inflation, and ask yourself if we do really make so much progress so fast, or if the standards have simply gone awry.
If you bothered to read the article you would learn they specifically discuss this. Their model is more advanced and actually realized the previous understanding was too naive and simplistic. The bubbles do not totally collapse but break into a wide variety of sizes and it is the collapse of bubbles in a specific range of sizes that creates the sound.
I suppose when Einstein published his theory of relativity you would have commented that this has been known for hundreds of years by Newton.
What I said is perfectly understood by any proper scientist.
Well Brenda - not everyone here is a scientist. And those of us who are find you to be a tad lacking. As well as making an egregious error in assuming what scientists do or do not know. They are not all fountains of identical knowledge.
But enough of calling you out - let's delve into your writing.
First, it it those people's duty to look up the possible references, if they want to style themselves as, you know, scientists; since this is very old news, and I'm not the one at fault, I won't spend the time required to find the old papers.
Well lookie here! A "proper scientist" who refuses to provide citations! There was a word for people like you around campus.
Unemployed.
I have always maintained that a good scientist or researcher should be able to explain to regular people (reasonably intelligent but ignorant of the matter at hand) what it is they are trying to say, to educate them to at least a minimal level of the subject.
But here you come in like the Grand Maximus lord of science, waving your massive science cock around like a bludgeon, slaying anyone who dares to disagree or even ask for clarification. It is useless, even self destructive as the immediate result is to look upon you as a mental masturbating douchenozzle who is first ridiculed, then laughed at, then ignored.
The shepherds did so well protecting the flock that the sheep no longer believed that wolves existed.
did scientists explain also why this sound is unbearable?
Slashdot, fix the reply notifications... You won't get away with it...
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We have understood this phenomena for decades and without the use of algorithms or mathematical formulas. I'm sorry you weren't born yet, and that your parents and teachers never bothered to, you know, teach you anything (especially humility). Millennials and their 'science' are just flipping broken, man. Thanks a lot, helicopters of the world. Here is the fruit of both your labors and your loins.
Great article admin. i love the way you summarized this post.
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You honestly expect them to argue for both sides of the debate?
We used to have a Bill of Rights. Now, with the rights gone, all we have left is the bill.
This is nowhere near new information.
I've known this for over 20 years -- pressure drops as the ends of the bones are levered apart and it passes some boil pressure point for some liquid or dissolved gas in there, which violently gassifies causing the pop.
They must have just defined these equations.
(-1: Post disagrees with my already-settled worldview) is not a valid mod option.
Awww come on, this is Slashdot. Do you expect people to read the referenced article? :-)) /. crowd for talking about a topic I know, and whose deep understanding is required to even express any meaningful opinion :-)))
And a a general response to various "penis size" comments, sorry to the
That said, I did read the article, and I stand to my points. I sort of half-retract on the first point, because the authors did read and reference previous literature, but you are right to mention that they acknowledge it was indeed simplistic; if only they woud draw the conclusion that it was maybe not the right kind of approach altogether, or at least not guaranteed to be sufficient.
Hell, I won't spend an hour on their "model" to eg check whether it even keeps balance of mass, since this is a common problem with some studies. They don't develop their own fluid mechanics approach, but just use an old "axisymmetric" solution as a given. Assuming this is even correct (it possibly is), the boundary conditions for those are often problematic (ie they have a major influence on the result, and finding the "right" ones can be tricky, even for people really specialized in fluid mechanics, which they don't seem to be). And they immediately reduce it to a "zero-dimensional" model, as with the rest of the study. As a counterexample, this approach is perfectly fine (provably) with Hertz contact laws, but then it's compressible elasticity. So from there, I usually grow tired and stop reading. There really is too much to say about the propensity of some physicists to systematically reduce everything to a neat zero-dimensional formula.
P.S. I like your comparison with classical mechanics and relativity. Irrelevant, but funny.
Who's my pwecious wittle scwipt kiddie? Gosh, they're just so adorable at that age.
So where do the original bubbles come from? They surely cannot remain within the synovial fluid pockets if they are bursting (thus causing the sounds which were mathematically modeled... because that's what they wanted to model, supposing that there are tiny bubbles in the first place).
What about the possibility that ligaments are also involved? And that the displacement of ligaments are 'slapping' the bubbles around? Or what about all of the other things in the human body?
How are they discovering this now?
This was the explanation given to me more than a decade ago when I was still in school.
Yes. This is standard. It's called "related work".
If you can't explain in your paper why you don't have any related work, and people point out that yes, this is nothing new and has been known for decades, it's your own job to fix your article with the correct related work.
I've seen people trying to reverse the burden of proof (i.e. "I claim and if you don't believe me, prove me wrong")
Wow, you're aware of the scientific method! Pretty impressive. Thanks for sharing.
Slashdot: providing anti-social weirdos a soapbox, since 1997.
And then "scientists" wonder why no one believes there shit any more. Coal workers are out of jobs, homosexuals are getting "married" and these idiots are wasting taxpayer dollars on researching useless bullshit.
We've known for at least a decade that it's micro-cavitation that causes the sound!
This is not news! Olds perhaps...
You have to be kidding! I read about this being discovered back in the 90s.
What I said is perfectly understood by any proper scientist.
The No True Scotsman defense.
First, it it those people's duty to look up the possible references
It falls onto the one making claims.
Ever heard about Navier-Stokes? Or any kind of mathematics?
Is that an attempt of Falacia ad Verecundiam? (appeal to authority)
Can these scientists say explain what is the sound of one hand clapping?
#DeleteChrome
Nah. I listen more to assholes than non assholes, because assholes are more often correct and fed up with the bullshit. Also, I'm an asshole myself and typically find myself agreeing when another asshole takes the time to rant about bullshit.
The original AC is correct, of course. This has been known for decades. Nothing new here, except maybe a crappy mathematical model for the sound, which is utterly pointless. It's a fucking pop.
The same principal is used to explain the inflation which accompanied the big bang. The nitrogen liquid (or initial elementary whatever) changes state under decompression, which is a phase change which has more energy in its ground state than in its previous state, which energy is released as inflation in the big bang, or a cracking sound in the joints.
I won't bother to look up the original reference(s). This has been known for decades, I read about it at least two decades ago. And this kind of "modeling" is, er, crude. Among other problems, it sorta oversimplifies the strain field in the surrounding fluid. Typical of would-be physicists.
The previous work is clearly pointed out in the paper, but of course, refusing to read it, you wouldnt know. Apparently (as described in the intro of the paper) this explanation for knuckle popping was known and widely accepted for a long time, but has more recently become contested. The mathematical modelling might be crude, but it predicts the spectrum to a degree which can decide between this old explanation and the newer other explanation, so it does the job. To do that, you mostly need to have a good handle on the short-time-scale dynamics of the cavitation. So as you are obviously an expert, here are two questions:
1) Not having read the paper, but only a summary based on a BBC article about the actual scientific article, how can you be sure strain fields have not been taken into account?
2) Assuming the liquid to be aqeuous, do you expect strain fields to be at all significant?
1) I _did_ read the article. As I stated above, it's typical physicist oversimplification. They shop for old literature in a field they I am not certain they master *ahem* to grab a zero-dimensional "model" for liquid flow between two spheres, sort of Reynolds lubrication. That's fine if you do have the skills to check if it even makes sense in the precise context, and that kind of skill requires PhD level in Mechanics. There is way too much to say here for a random /. comment, but as a mere example the "solution" they use might very well be unstable in various ways in this context, depending eg on boundary conditions or the precise geometry. I've seem so many papers ignoring that (in the sense of mathematical ignorance), and developing sophisticated models around a flow that cannot exist in the sense that any infinitesimal perturbation drives the flow away from it, fast. Really too much to say.
2) Aqueous or otherwise, it's certainly mosty dissipative, let's assume more or less complicated viscous. Given the probably very high rate of strain around a bubble whose diameter is rapidly evolving in the vicinity of zero, yes, the damping influence of viscosity might be important, and other neglected factors might as well. And again, I won't check the old reference they provide for the maximum pressure formula, but it wouldn't surprise me much if it didn't pass, say, balance of mass. :-))
You mileage may vary, mine is close to reset
So I guess I'm not part of the "in" crowd. I didn't know it for decades. Any chance I could still get some kind of proof?
Li'l hint why I'd insist: We used to know for centuries, not just decades, that the Earth is the center of the universe.
We used to have a Bill of Rights. Now, with the rights gone, all we have left is the bill.