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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.
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.
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.
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?...
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.
Eric Idle?
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
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...
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.
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.
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.
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.
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.