I just performed a quick literature review of the relevant threads. I found this, but I don’t think the matter was resolved.
Someone in that thread speculated that the gases in farts are lighter-than-air. I’m skeptical; it’s mainly methane, right? And methane is made of heavier atoms than nitrogen and oxygen, which make up most of our air.
But I’m willing to be convinced. Another possibly confounding variable is that fart gases are slightly compressed while inside the body.
Surely there’s a government study that will answer this question…
Hmm, let’s see.
“Hydrogen, carbon dioxide, methane and swallowed nitrogen comprise 99% of colon gas. The remaining 1% consists of trace gases that compensate for their small quantities by their strong odors.”
Methane is only about half as dense as air at Standard Temperature and Pressure (room temp, one atmosphere of pressure). [In case you were wondering, methane is one carbon and four hydrogen, total atomic weight about 12+4=16; air is mostly molecules of nitrogen, two atoms each, with a total atomic weight of 14+14=28]
Hydrogen is also much lighter than air, as all zeppelin fans know (finding the actual density is left as an exercise for the reader). Nitrogen is of course the same density as air. The trace gases are going to be heavier than air, but at only one percent, it’s safe to assume that overall flatulence gas is lighter than air at STP.
However, inside the body, it isn’t at STP. It’s a little warmer, therefore less dense, but not too much, so we can probably ignore that.
But it is at higher pressure (if the intestinal gas isn’t at higher pressure than one atmosphere, it won’t be expelled, so no fart). At the higher pressure, the gas will be denser.
Unfortunately, I have no idea what the pressure is like within the human colon, so have no way of knowing whether the increased density is enough to reach the density of air.
Either Qagdop will come in with an authoritative cite on the average human colon gas pressure, or we’ll have to look for volunteer Dopers to be outfitted with pressure gauges.
Do you mean weight or mass? Should I do nothing but expel gas from my body, my mass will decrease. As for farts, I dunno their composition has ever been adequately determined.
Ignoring the 20° or so of temperature difference (less than 10%, which is well within our margin of error), if the gas were all methane, then you’d need almost two atmospheres of pressure in the colon to get to neutral bouyancy. According to this site, only aout 10% of flatus is produced within the digestive system. So the gas in your digestive system is about 95% as dense as the air and would require relatively little pressure within the colon to become more dense than air. It looks like farts do make you lighter (under normal atmospheric conditions).
In my experience, the temperature (and hence density) of farts can vary by orders of magnitude. I think we’ve all experienced the occasional “blowtorch”. THis would seem to make the question unanswerable in general.
I meant weight. Obviously the mass would decrease, as a simple matter of physics (and a simple physics of matter).
Hyperelastic, I don’t know how you can say the temperature would vary “by orders of magnitude.” That’s just not possible; the temperature will always be within a few degrees of 98.6°.