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  • Director Steve Belfer
  • Animator James Jacob, Michelle Tessier
  • Educator Eleanor Nelsen
  • Sound Designer Cem Misirlioglu
  • Narrator Addison Anderson


Additional Resources for you to Explore
Want to learn the latest on this topic? Read the recent publication: Real Time Visualization of Joint Cavitation aka “knuckle cracking!” Then listen to the latest Morning Edition at NPR: Why Knuckles Crack! Scroll down at the site and watch an MRI of knuckle cracking in real time to see the “pop” during the “pull my finger study!”

Here’s another interesting physiological phenomenon that has to do with gas solubility: decompression sickness, or “the bends.” When divers are deep underwater, they experience ambient pressure much higher than it is on land. The divers’ air tanks must be at a correspondingly high pressure to allow air to flow out of the tank into the mask. Learn about the “bends” from the U.S. Coast Guard. Gas solubility is directly proportional to pressure, so when divers breathe the compressed air, much more of it dissolves in their fluids and tissues. If the diver returns to the surface too quickly, the rapid change in pressure causes all those dissolved gases to come out of solution and form bubbles—like the ones that form when you crack your knuckles, but on a much larger scale. Watch this TED Ed lesson: The effects of underwater pressure on the body to learn more.

These escaping bubbles can cause a variety of symptoms including joint pain, rashes, shortness of breath, headaches, and fatigue. In severe cases, the bubbles can cause lung damage, paralysis, or embolism. But if the diver is careful to ascend slowly, the extra dissolved gas can simply be exchanged harmlessly through the lungs. Interestingly, divers can also avoid “the bends” by breathing a mixture of oxygen and helium, instead of oxygen and nitrogen: helium is much less soluble in blood, so there wouldn’t be as much dissolved gas to escape when the pressure returned to normal. Visit this site to learn more about avoiding decompression sickness.

Ever wonder how underwater organisms avoid the bends? Read about Penguins here and Sea Lions here! What can we learn from them that could potentially help humans?

Decompression sickness can also occur when going from standard atmospheric pressure to much lower pressure, like those higher in the atmosphere. This is why aircraft cabins are pressurized—not quite to the pressure at sea level, but more like what you might find at the top of a medium-sized mountain. This is enough to keep most people from experiencing decompression sickness—unless, that is, you’ve been diving recently! Read this FAA Brochure on Altitude Induced Decompression Sickness and find out the details.