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Why Your Knuckles Make That Satisfying Cracking Sound, According to Science

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Scientific curiosity is not always burdened by matters of great consequence. Over the years, considerable money and time has been applied to matters involving facial recognition between sheep, whether the flow of urine is impeded by someone watching you pee, and whether humans can capably swim in a pool full of syrup. (They can, almost as well as water.)

Now, researchers from Stanford University and Ecole Polytechnique in France have turned the roving eye of science to the phenomenon of knuckle-cracking. According to Gizmodo, a computer simulation was created to confirm an earlier theory that the audible noise that comes from the human hand after putting pressure on the knuckle was the result of gas bubbles popping inside the finger joint.

Conclusion: Probably true.

The study, published in Scientific Reports, demonstrated that microscopic bubbles inside the lubricating synovial fluid of the joint collapse when a knuckle-cracking session commences. To use an imperfect analogy, the cavitation bubbles are like the body’s Bubble Wrap. Popping them produces an audible—and for many, a very pleasing—sound.

To compile data, researchers took geometric representations of the joint's movements during a cracking session and turned them into mathematical equations. (Imaging has not been shown to be very productive in this field, as the crack takes only about 300 milliseconds and is not easily visualized.) The software models demonstrated that pressure shifts in the joint fluid increase pressure on the gas bubbles. Unlike packing material, however, the gas bubbles don't really perforate—they experience a partial collapse but remain suspended in the joint.

So does this solve the mystery surrounding cracked knuckles? Not entirely. Because it was a simulation, there's a possibility of mathematical error. Proponents of alternative theories—that it's not bubbles collapsing but bubbles being created that produce the noise—feel there's more work to be done. We can only hope a complete understanding will come in our lifetime. Fingers crossed. And cracking.

[h/t Gizmodo]

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The Surprising Link Between Language and Depression
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Skim through the poems of Sylvia Plath, the lyrics of Kurt Cobain, or posts on an internet forum dedicated to depression, and you'll probably start to see some commonalities. That's because there's a particular way that people with clinical depression communicate, whether they're speaking or writing, and psychologists believe they now understand the link between the two.

According to a recent study published in Clinical Psychological Science, there are certain "markers" in a person's parlance that may point to symptoms of clinical depression. Researchers used automated text analysis methods to comb through large quantities of posts in 63 internet forums with more than 6400 members, searching for certain words and phrases. They also noted average sentence length, grammatical patterns, and other factors.

What researchers found was that a person's use (or overuse) of first-person pronouns can provide some insight into the state of their mental health. People with clinical depression tend to use more first-person singular pronouns, such as "I" and "me," and fewer third-person pronouns, like "they," "he," or "she." As Mohammed Al-Mosaiwi, a Ph.D. candidate in psychology at the University of Reading and the head of the study, writes in a post for IFL Science:

"This pattern of pronoun use suggests people with depression are more focused on themselves, and less connected with others. Researchers have reported that pronouns are actually more reliable in identifying depression than negative emotion words."

What remains unclear, though, is whether people who are more focused on themselves tend to depression, or if depression turns a person's focus on themselves. Perhaps unsurprisingly, people with depression also use more negative descriptors, like "lonely" and "miserable."

But, Al-Mosaiwi notes, it's hardly the most important clue when using language to assess clinical depression. Far better indicators, he says, are the presence of "absolutist words" in a person's speech or writing, such as "always," "constantly," and "completely." When overused, they tend to indicate that someone has a "black-and-white view of the world," Al-Mosaiwi says. An analysis of posts on different internet forums found that absolutist words were 50 percent more prevalent on anxiety and depression forums, and 80 percent more prevalent on suicidal ideation forums.

Researchers hope these types of classifications, supported by computerized methods, will prove more and more beneficial in a clinical setting.

[h/t IFL Science]

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The ‘Scully Effect’ Is Real: Female X-Files Fans More Likely to Go Into STEM
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FBI agent Dana Scully is more than just a role model for remaining professional when a colleague won't stop talking about his vast governmental conspiracy theories. The skeptical doctor played by Gillian Anderson on The X-Files helped inspire women to go into STEM (science, technology, engineering, and math) careers, according to a new report [PDF] from the Geena Davis Institute on Gender in Media, which we spotted at Fast Company.

“In the world of entertainment media, where scientists are often portrayed as white men wearing white coats and working alone in labs, Scully stood out in the 1990s as the only female STEM character in a prominent, prime-time television role,” the report explains. Previously, anecdotal evidence has pointed to the existence of a “Scully effect,” in which the measured TV scientist—with her detailed note-taking, evidence-based approach, and desire to autopsy everything—inspired women to seek out their own science careers. This report provides the hard data.

The Geena Davis Institute surveyed more than 2000 women in the U.S. above the age of 25, a significant portion of whom were viewers of The X-Files (68 percent) and women who had studied for or were in STEM careers (49 percent). While the survey didn’t ask women whether watching Dana Scully on The X-Files directly influenced their decision to be a scientist, the results hint that seeing a character like her on TV regularly did affect them. Women who watched more of the show were more likely to say they were interested in STEM, more likely to have studied a STEM field in college, and more likely to have worked in a STEM field after college.

While it’s hard to draw a direct line of causation there—women who are interested in science might just be more inclined to watch a sci-fi show like The X-Files than women who grow up to be historians—viewers also tended to say Scully gave them positive impressions of women in science. More than half of respondents who were familiar with Scully’s character said she increased their confidence in succeeding in a male-dominated profession. More than 60 percent of the respondents said she increased their belief in the importance of STEM. And when asked to describe her, they were most likely to say she was “smart” and “intelligent” before any other adjective.

STEM fields are still overwhelmingly male, and governments, nonprofits, schools, activists, and some tech companies have been pushing to make the field more diverse by recruiting and retaining more female talent. While the desire to become a doctor or an engineer isn’t the only thing keeping STEM a boy’s club, women also need more role models in the fields whose success and accomplishments they can look up to. Even if some of those role models are fictional.

Now that The X-Files has returned to Fox, perhaps Dana Scully will have an opportunity to shepherd a whole new generation of women into the sciences.

[h/t Fast Company]

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