Let’s look at the answer to the last [Listening] episode first.

….the wealth of the poorest half…

…the 1 percent would soon…

I guess many of you got the correct answers!

Here comes the practice for today. Please LISTEN PATIENTLY. And the question goes to two words I have blanked in the script below.


The Secret Of The Knuckles Cracking

Couple years back, Vinny Suja was taking a biomechanics class at the French Polytechnic School, outside Paris. And he was on the hunt for the perfect class project.

He was cracking his knuckles one day and that’s when he realized—”Huh, that’s interesting.” And so a project was born: the physics of knuckle cracking. It’s ??? (one word missing) a subject of intense scientific investigation.

Back in 1971, scientists figured they knew how it worked: the cracking sound was caused by bubbles popping within the fluid surrounding the knuckles. Or so they thought—because in 2015 shots were fired, in the form of MRI visualization of the knuckles post-cracking.

In fact, the bubbles were still there. The whole process happens too fast for imaging technology to visualize in real time—you’d need to shoot at 1,200 frames per ??? (one word missing), 10 times faster than the best x-ray and MRI machines on the market.

So, using mathematical models, Suja and his colleague Abdul Barakat found that just a partial collapse of the bubbles could cause cracking sounds of the same degree, which might explain why the 2015 researchers still saw bubbles after the crack.

Further modeling of bubble behavior, both pre- and post-pop, will be needed, they say before they’re confident that they’ve truly cracked the case.

Don’t forget to comment with your answers below and try to be the lucky first one.🙂

See you next time! 😀