Does the act of farting make you less buoyant?

I was thinking about the question I asked here:

Even before quasar’s signature line, I wondered if the same principle applied to the gaseous mixture contained in a fart.

Are farts buoyant? When we ‘let er’ rip’ are we making ourselves “weigh” more. Or is the reverse true?

I could have sworn this was indirectly addressed in one of Cecil’s columns, but I couldn’t find it in the archive just now. In any case, the answer depends on the composition of the gas and whether it’s at or above atmospheric pressure in your intestines. Methane, for example, is somewhat lighter than air (unless your intestines have it compressed too much), so if you’ve got some methane in you at atmospheric pressure, it’s making you lighter. Some intestinal gas is hydrogen, which is much lighter than air, and I think some is carbon dioxide, which is heavier than air. So I think it’s possible that sometimes farting makes you lighter and sometimes it makes you heavier, but I have no idea what the pressure is like in your intestines.

Since it is highly unlikely that your intestines have compressed the gasses within them to a density of 1, which is the approximate density of an average human body, the relative pressure of your intestine is trivial as a factor.

The volume of your body is not decreased on a one for one basis for the volume of gas released in a fart. However, it will decrease by some amount. The amount of decrease will be greater than the volume of an equivalent weight of water. You will become less buoyant. As your digestion produces more gas, you will regain that buoyancy, until that gas is released as well.

If someone cares to supply average volume figures for human flatulence, we can run the numbers to see how many farts it takes to sink the average asshole over his head.

How’s that for fighting ignorance?

I ALWAYS feel less buoyant after letting off a rip-snorter, especially in crowded, well lighted settings.

The guilt “weighs” heavily on me!

I think this is along the line of what Triskadecamus was talking about but I’ll try and elaborate regardless.

Things do not float because they possess gas. The only thing to take into account regarding floating is how much the object weighs and how much water it displaces. This is most clearly seen with scuba tanks. An empty scuba tank (some of them anyway) can float. Fill it with air and it will sink. Why? Because air weighs something and the tank, when filled doesn’t expand in any appreciable fashion. Basically it displaces the same amount of water as it did empty but now it weighs more so it sinks.

So, when you fart you weigh less. Did the fart inside of you appreciably expand your body size to displace more water than the fart weighs? Frankly I have no idea. There are so many other variables (regular breathing, firm muscle tone vs. flabby, etc.) that’d swamp the reality out that I doubt you could even perform a reliable test of this.

My guess is you’d weigh less but still displace the same amount of water (the fart didn’t increase your body size) so you’d be more likely to float after the fart. Of course, if you just had a bean burrito the size of your head then all bets are off.

It looks like I read the OP a little different from everyone else. I think it’s self-evident that intestinal gas increases your buoyancy in water. There’s no way the gas inside you is going to be anywhere near as dense as water, of course.

What I was talking about was buoyancy and weight in air. Just as helium in a balloon makes the balloon buoyant so that it floats in air, hydrogen gas in your intestines would make you lighter as long as it wasn’t compressed more than a certain amount by the pressure inside you. So intestinal gas always makes you lighter if you’re in water, but it might or might not if you’re on dry land.


Intestinal gas would make you heavier in water or on dry land. Just as a baloon full of helium weighs more than an empty ballon it isn’t weight that is important but density. Your volume will go down with a negligable decrease in weight so you lose buoyancy, seems pretty obvious.

The OP said, "When we ‘let er’ rip’ are we making ourselves “weigh” more?

You need to learn the difference between mass and weight before you go saying “Ack” to anyone. Have you ever had a grade-school physics class? The mass of a helium balloon is more than the mass of an empty balloon because there’s more matter there. But the weight of a helium balloon is less than the weight of an empty one. Weight means how hard an object pushes down on whatever is under it and is not the same as mass. An object that is less dense than air, like a helium balloon, weighs less than it would if it were denser than air because of the buoyancy of the air.

So passing gas always decreases your mass, but it won’t decrease your weight unless the gas is denser than the medium that surrounds you.

And when you say that intestinal gas makes you heavier, but that losing the gas makes you lose bouyancy, you’re contradicting yourself since buoyancy is the opposite of heaviness.

You need to be more careful before you get even snottier than I was. The definition of weight is the force of attraction between an object and the earth. The fact that a helium ballon cannot be easily weighed on a traditional scale without placing it in a vacuum does not change this.

I was not contradicting myself at all.