4 ms·

tl;dr it's from creating cavities not popping bubbles. Not creating and popping them, but rather that's the sound of creation.

by abalone 12y ago

erikb 12y ago
Thanks. Can you explain it in simpler English please? I'm not native and googling for "cavity" results in pictures of teeth with holes not ankles. If I transfer "hole" to the topic of ankle I don't see the difference between the bubble and the hole theory.
- jrk_ 12y ago
  For more awesomeness have a look at this: http://en.wikipedia.org/wiki/VA-111_Shkval http://en.wikipedia.org/wiki/VA-111_Shkval
- astral303 12y ago
  Bubble theory: bubble collapses (hole was there, hole stops being there after collapse). Hole theory: hole appears, (no hole before cracking, hole forms after cracking). However, "hole" is usually used when the empty space goes entirely through the object, whereas a cavity means that there is an end/depth to it. For example, digging a hole in a sand is really also (more accurately) digging a cavity.
- Kluny 12y ago
  "Cavity" literally means "an empty space". Bones are hollow but filled with marrow. To create a cavity, you have to stretch the bone so that there isn't enough marrow to fill it up.
  - loco5niner 12y ago
    ;-) Pretty sure we're talking about cavities forming _between_ bones. Stretching a bone out enough to to create a cavity "within the marrow" does not sound appealing in the least (yikes)
    - Kluny 12y ago
      Oh yeah? I was wondering about that bit! ;) Must have misread something.
    - andrey-p 12y ago
      Pretty sure the crack from that would be much louder.
- corysama 12y ago
  Think about bubbles in a bottle of carbonated soda. Before you open the bottle, the carbonation is a liquid inside of the water because of the pressure inside the bottle. When you open the bottle, the pressure drops and the carbonation converts to a gas and becomes bubbles. But, imagine if instead of opening the bottle, you just somehow reduced the pressure then quickly increased it back to what it originally was. The carbonation would go from liquid -> gas -> liquid very quickly. CO2 bubbles would form then collapse. Converting from liquid to gas is not a special property of CO2. There are liquids in your joints that will convert to gas if you drop the pressure. That's what happens for an instant when you crack your knuckles. What you are hearing is the bubbles of gas collapsing as the gas converts back to liquid.
  - Crito 12y ago
    What they actually found in this MRI study is that the bubbles stick around for several minutes, slowly dissolving back into the fluid. They don't immediately collapse as you would expect. The sound seems to come from the very rapid expansion. The time it takes for the bubbles to dissolve again seems to be responsible for the "cool-down" period that you experience between cracks.
- fapjacks 12y ago
  This will sound weird, but... Have you ever stabbed a big piece of meat with a thick knife? And you know the sort of sucking sound it makes when you extract your knife from the meat? This is similar to what's happening inside your knuckles. The sudden in-rushing of gas into the space between your knuckles.

tl;dr it's from creating cavities not popping bubbles. Not creating and popping them, but rather that's the sound of creation.

by abalone 12y ago

tl;dr it's from creating cavities not popping bubbles. Not creating and popping them, but rather that's the sound of creation.

erikb 12y ago

Thanks. Can you explain it in simpler English please? I'm not native and googling for "cavity" results in pictures of teeth with holes not ankles. If I transfer "hole" to the topic of ankle I don't see the difference between the bubble and the hole theory.

jrk_ 12y ago
For more awesomeness have a look at this: http://en.wikipedia.org/wiki/VA-111_Shkval http://en.wikipedia.org/wiki/VA-111_Shkval
astral303 12y ago
Bubble theory: bubble collapses (hole was there, hole stops being there after collapse). Hole theory: hole appears, (no hole before cracking, hole forms after cracking). However, "hole" is usually used when the empty space goes entirely through the object, whereas a cavity means that there is an end/depth to it. For example, digging a hole in a sand is really also (more accurately) digging a cavity.
Kluny 12y ago
"Cavity" literally means "an empty space". Bones are hollow but filled with marrow. To create a cavity, you have to stretch the bone so that there isn't enough marrow to fill it up.
- loco5niner 12y ago
  ;-) Pretty sure we're talking about cavities forming _between_ bones. Stretching a bone out enough to to create a cavity "within the marrow" does not sound appealing in the least (yikes)
  - Kluny 12y ago
    Oh yeah? I was wondering about that bit! ;) Must have misread something.
  - andrey-p 12y ago
    Pretty sure the crack from that would be much louder.
corysama 12y ago
Think about bubbles in a bottle of carbonated soda. Before you open the bottle, the carbonation is a liquid inside of the water because of the pressure inside the bottle. When you open the bottle, the pressure drops and the carbonation converts to a gas and becomes bubbles. But, imagine if instead of opening the bottle, you just somehow reduced the pressure then quickly increased it back to what it originally was. The carbonation would go from liquid -> gas -> liquid very quickly. CO2 bubbles would form then collapse. Converting from liquid to gas is not a special property of CO2. There are liquids in your joints that will convert to gas if you drop the pressure. That's what happens for an instant when you crack your knuckles. What you are hearing is the bubbles of gas collapsing as the gas converts back to liquid.
- Crito 12y ago
  What they actually found in this MRI study is that the bubbles stick around for several minutes, slowly dissolving back into the fluid. They don't immediately collapse as you would expect. The sound seems to come from the very rapid expansion. The time it takes for the bubbles to dissolve again seems to be responsible for the "cool-down" period that you experience between cracks.
fapjacks 12y ago
This will sound weird, but... Have you ever stabbed a big piece of meat with a thick knife? And you know the sort of sucking sound it makes when you extract your knife from the meat? This is similar to what's happening inside your knuckles. The sudden in-rushing of gas into the space between your knuckles.