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What causes the sound of cracking knuckles ?


Posted on Thursday, 29 March, 2018 | Comment icon 12 comments

Are you able to crack your knuckles ? Image Credit: CC BY 2.0 Jaysin Trevino
Scientists have come up with three mathematical equations to explain the sound of a cracked knuckle.
It's one of the most annoying sounds a person can make, but despite almost a century of debate over exactly what produces the distinctive 'popping' sound when someone cracks their knuckles, scientists are still finding new ways of approaching and investigating the phenomenon.

Most recently, French science student Vineeth Chandran Suja and his lecturer Dr Abdul Barakat decided to investigate knuckle-cracking and managed to explain it by way of three equations.

"The first equation describes the pressure variations inside our joint when we crack our knuckles," said Suja. "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."

These equations, he argues, build up a complete mathematical model of the knuckle-cracking sound.

"When we crack our knuckles we're actually pulling apart our joints," he said. "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."

Source: BBC News | Comments (12)

Tags: Knuckles

Recent comments on this story
Comment icon #3 Posted by pallidin on 29 March, 2018, 23:38
Yeah. Once I find a knuckle that "cracks", I just keep doing it until it goes away and it feels better. I heard that this is not harmful at all, but, not sure. Anyone know?
Comment icon #4 Posted by Hankenhunter on 30 March, 2018, 8:27
Gawd, when I get up in the morning I sound like snack time at the Orville Reddenbacher factory. Even my old arthritic dog looks at me as if to say, "Whoa dude, sucks to be you." Hank
Comment icon #5 Posted by quasar_kid on 30 March, 2018, 9:47
I can better explain it in my own language but I'll try in English. When you crack your knuckles fluid is being released that holds the fingerbones loosely together, if you do it for years on end it can cause severe arthritis because the gap between your bones can't close properly anymore which results in your fingers being "bent".
Comment icon #6 Posted by DieChecker on 30 March, 2018, 11:40
I've always heard it is bad for your joints, but here I am almost 50 and my fingers are still pain free.... I guess I'll keep cracking them. I also can pop my elbows, shoulders, ankles and feet bones. The elbows are particularly loud. Like a knuckle pop times three.
Comment icon #7 Posted by Myles on 30 March, 2018, 12:09
I crack too much I think. Neck, back, fingers, toes, ankles, knees and a weird one - my Xiphoid process.  i believe that is what it is called.  The little bone below the sternum. 
Comment icon #8 Posted by DieChecker on 30 March, 2018, 15:52
Oh yeah. I can crack the upper part of my sternum too, but that's due to the surgery I had a couple years back.   It is not too much unless it is hurting you, I think. 
Comment icon #9 Posted by Rlyeh on 30 March, 2018, 18:52
That's a myth. https://www.scientificamerican.com/article/crack-research/
Comment icon #10 Posted by Katniss on 2 April, 2018, 5:28
Hah! I knew it!
Comment icon #11 Posted by I'mConvinced on 3 April, 2018, 14:38
I really had to fight hard to even read this thread. I've avoided it ever since I saw the article on the front page but today was the day. If you pop things then I hate you. I hate the sound, I hate the feeling it generates inside my head, I hate the smug looks on peoples faces while they DO IT ON PURPOSE to screw with you. Yes, I hate you all. That said, behind your hideous joint cracking craziness I'm sure you're all good people. Just please be those good people very, very far away from me . And yes, I'm Misophonic.
Comment icon #12 Posted by DieChecker on 5 April, 2018, 13:39
I soooooooooooo..... Want to post youtube videos of people cracking knuckles now.... 


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