Maggie Koerth-Baker has a great piece up at the 538 blog: "How Big Is A Fart? Somewhere Between A Bottle Of Nail Polish And A Can Of Soda." It's well researched, digging into the biomedical literature with verve. And it's great that she gives the answer a context, it's easier to visualize a bottle of nail polish than a 17 ml blob for most people, me included.
I'm not at all surprised at what you can find in the primary literature (I tracked down papers on exploding people and deuterated dogs1 for my introductory chemistry class last spring). The piece is the first in a series Science Question From A Toddler, though I suspect that people somewhat past the target age group (5 and under) would be interested in the answer to this question, too.
In a footnote Koerth-Baker suggests that farts in the body would be smaller because the gas would be compressed inside the body. But the pressure inside the human colon is the same as atmospheric pressure. Farts and burps keep it that way. What's different is the temperature, higher inside the body by about 30oF (17oC). Gases expand at higher temperatures. You can use Charles' law to figure out by how much the volume changes with changes in temperature: V2=(T2/T1)V2
The researchers measured the volume of the farts at room temperature (I read the paper!), so the volume of a fart should be slightly larger in the body than the reported numbers by a factor of (310/293) or about 6% larger. So how big is a fart? Just before exit, it's about the size of a 14 ounce ketchup bottle for the largest one in the 1997 study.
Read full article at: http://cultureofchemistry.fieldofscience.com/
Related articles: Physical Chemistry
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