Do you become heavier or lighter when you fart?

Question

Its all gas - and lighter than air gas....so do you become heavier from releasing that light gas, or lighter (this is without follow through of course...)

Answer 1

Never thought about it coz all I feel is relieved!!! lol

Answer 2

This problem is best described by Archimedes principle - Upthrust is equal volume of liquid or gas displaced.

So we need to know what is the density of the fart inside the body. This has two parts it's chemical composition and it's pressure:

1) What is fart gas made of?

[1] The composition of fart gas is highly variable. Most of the air we swallow, especially the oxygen component, is absorbed by the body before the gas gets into the intestines. By the time the air reaches the large intestine, most of what is left is nitrogen. Chemical reactions between stomach acid and intestinal fluids may produce carbon dioxide, which is also a component of air and a product of bacterial action. Bacteria also produce hydrogen and methane.
But the relative proportions of these gases that emerge from our anal opening depend on several factors: what we ate, how much air we swallowed, what kinds of bacteria we have in our intestines, and how long we hold in the fart.

Avogadro's principle says the weights of a fixed volume of gas at teh same pressure and temperature is dependent on its atomic mass.

Nitrogen (N2) - molecular weight 28
Oxygen (O2) - molecular weight 32
Hydrogen (H2) - moelcular weight 2
Methane (CH4) - molecular weight 14
Carbon dioxide (CO2) - moelcular weight 48

Air is roughly 80% Nitrogen and 20% Oxygen.
Fart gasses are 90% atmospheric and 10% generated by bacteria. [2]
Assuming this is made equally of Hydrogen and Methane. 90% N2 + 5% H2 + 5% CH4

Average molecular Weight of air = 28.8
Average moelcualr weight of fart = 26

This makes fart gas 10% lighter than air.

2) What is the pressure?
> The intestine squeezes its contents toward the anus in a series of contractions, a process called peristalsis. The process is stimulated by eating, which is why we often need to poop and fart right after a meal. Peristalsis creates a zone of high pressure, forcing all intestinal contents, gas included, to move towards a region of lower pressure, which is toward the anus.
The median amplitude of pressure waves associated with intenstine is 10kPa. [4] This is 10% above atmospheric pressure.
However in an airplane the air pressure is usually 10psi or 30% below sea level pressure. [3]

The answer is a close call at sea level, you may be slightly heavier or slightly lighter depending on the chemical composition of the gases and the pressure in your intenstine. However in an airplane you almost certainly will get lighter.

To comment on Simons S's last point - whether the bowel collapses or takes in air - this will give the same weight as the air it as long as it is kept at the same pressure as the external atosphere. Otherwise it would be like pumping air into a tyre - the tyre does start to get heavier once the pressure exceeds one atmosphere.

Answer 3

Your mass is reduced as the gas has mass and has left your body.

However, this doesn't mean that if you were to get on some scales and weigh yourself before and after that your measured weight would go down. It is possible that the gas you released was providing buoyancy that reduced your weight (recall Archimedes principle that the buoyancy force is equal to the weight of the fluid, in this case air, that it has displaced).

If the buoyancy of the gas (while inside you) is greater than it's weight (i.e it is providing an net up force) then your weight measured on the scales will increase when farting.

If the buoyancy of the gas is less than it's weight (i.e. it is providing a net down force) then your weight measured on the scales will go down.

Notice in these arguments there are important qualifiers. For example we are talking about the buoyancy of the gas while it is inside you. The gas is likely to be under pressure inside you and confined to a certain volume. Just because the gas floats while it is outside your body does not mean that it floats at the pressure, volume and temperature within your body. Also I am talking about your weight measured on the scales, usually when we talk about weight we mean the force on your body due to gravity, we don't consider the "negative weight" caused by buoyancy. Finally, I haven't considered what replaces the fart gas once it leaves your body. It could be that your bowels collapse to fill the gap, it could be that air rushes in to fill the gap. Unfortuantely to answer this you need a biologist, not a physicist.

Answer 4

Theoretically, you should become lighter. Not to mention the extent of course (it will very very small)

Here, i m comparing your weight the instant before you fart and the instant after you fart.
Since mass is the measure of the total amount of substance in your body, letting out gas is definitely a loss of mass, as (to wdzone) gas HAS weight. Since mass and weight is proportional, a loss in mass will lead to a loss in weight.

Answer 5

You become lighter as gas has mass as well. It's like a balloon, a empty balloon has less mass than a helium filled ballon. it's just that the helium filled balloon will fly up in the air as it's mass/volume is lower than the mass/volume of the same volume of air

Answer 6

Are you trying to find some way to cheat the weight scale?

Answer 7

you will become lighter.

Athough at atmosperic pressure farts are lighter than air, they are compressed in your body, making them denser than air.

If they weren't compressed thenyou wouldn't get that farting sound!!

Answer 8

It would seem lighter

Answer 9

that is possibly the best question on this site - ever!!!!!!

(sorry I cant help, but I think you'd have to ask a ery dedicated doctor to do some measurements)

Answer 10

miss ktps i love your questions lol. anyways im not sure about this 1 but it certainly soothes my tummy ache after a long rasper