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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.
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've seen numerous results of research regarding this subject at least a decade ago already drawing the same conclusions.
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.
> 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.