Our chemistry teacher presented us with this problem today:
Suppose a man is standing on a scale, a VERY accurate scale. If he “passes” some gas, would the reading on the scale go up or down and why?
Possibly if the scale was accurate down to fractional milligrams the expulsion could provide enough lift to decrease your weight on the scale for a moment.
One way to look at it.Just by measuring weight of gas expelled could hardly have any effect-since you’d probably be replacing that gas with breathing.Don’t see how it could make you heavier,unless that gas force could push the scale surface down slightly.Since no mention was made as to where the expulsion originated,my WAG is propulsion levitated/decreased gravity for the person for a moment on the scale,making him slightly lighter,at the time.
Accounting for the breathing, there would still be a change in weight.
The question would be should the weight reading increase or decrease?
Example: If the gas passed is all helium, the person expelling it would be less boyant with respect to the air around him, making him appear heavier. However, if the gas was some other extreme, say radon, expelling the gas would make him appear lighter.
Ok,ok, the radon example assumes that the gas isn’t falling from its “origin” and pooling on the scale platform.
Basically the solution depends on the boyancy of the expelled gas: if the gas is lighter than air, the person will appear heavier.
Also, this assumes that the compression applied to the gas pocket is negligible.
I used to work at a scale/balance facility and the boyancy of regular air IS a factor while making very small measurements.
Accounting for the breathing, there would still be a change in weight.
The question would be should the weight reading increase or decrease?
Example: If the gas passed is all helium, the person expelling it would be less boyant with respect to the air around him, making him appear heavier. However, if the gas was some other extreme, say radon, expelling the gas would make him appear lighter.
Ok,ok, the radon example assumes that the gas isn’t falling from its “origin” and pooling on the scale platform.
Basically the solution depends on the boyancy of the expelled gas: if the gas is lighter than air, the person will appear heavier.
Also, this assumes that the compression applied to the gas pocket is negligible.
I used to work at a scale/balance facility and the boyancy of regular air IS a factor while making very small measurements.
“Passing” gas implies farting. The Master gives us a list of the ingredients of a fart here*. Careful reading of such should lead one to the conclusion that farts are lighter than air.
*[sub]Try as I might, I was unable to find the specific column in which he actually addressed the problem posited in the OP.[/sub]
BTW, a couple of things, QuaHKN: First, welcome to the SDMB, and may you have a good time fighting ignorance and having your own ignorance fought.
Second, your OP comes perilously close to what is thought of around here as “asking people to do your homework.” The practice, while impossible to completely eliminate, is not encouraged. A word to the wise.
Once again, welcome, enjoy yourself, make yourself at home (and useful, if you get the opportunity).
I don’t know about fart being lighter than air. The Master’s column mentions hydrogen, CO2 and methane. Methane and hydrogen are lighter than air but CO2 is heavier, so depending on their proportions the mixture could be lighter or heavier than air.
You weigh less after the fart. even lighter than air gas has weight, and when that mass is expelled, you lose the weight of the gas, even if it is a fraction of a milligram.
hrm, didn’t read OP well enough, I guess it would depend on how much volume you lose when you expel the fart - I assume the gas is pushing your abdomen out while it is inside and your body loses a bit of volume once the gas escapes… is that a true assumption? Then if the loss in weight/volume relative to atmosphere’s weight/volume would determine if the scale would go up/down.
We can assume the gas is under a pressure greater than the surrounding air while it is in your body. Otherwise, it wouldn’t leave your body forcefully like it does. Therefore, it has density greater than the surrounding air. So the gas decreases in density as it leaves your body. From this it follows that the reading on the scale will decrease (although very slightly) when you pass gas.
I think to know the answer we’d have to know exactly how much pressure the gas is under while in your intestines. If it’s compressed enough to be heavier than the surrounding air, you’d be lighter after farting. If it’s still lighter than air while in your body, you’d be heavier after farting.
Sooo… Just what is the pressure behind a good, vigorous fart?
Buoyancy is not an issue for compressed gases. Your volume remains constant, you lose mass, you get lighter, period.
C’mon, this is the same concept as the "helium tank’ thread.
Thanks for the warm welcome, kaylasdad99 and the replies from the rest of the posters. I just wanted to clarify that my lab partner and I have already worked on this problem, came up with our hypothesis (although it may not be very scientific), and wanted to see what others could come up with, so I’d have something to compare it to.
Thanks again for all the information.
jnglmassiv: “If the gas passed is all helium”…
If I ever cut a helium fart, you’ll not be able to read my scale because it’ll be bouncing too much from my laughter.
Eeeeeeeeeeeeeeeeeep!
I’m hearing the sound of air escaping sharply from a balloon. Vrrrrrrr!
“Rigel” on Farscape farted helium.
This is true, but I think the pressure inside the intestine is so low (i.e. close to the atmospheric pressure) that fart should be approximated as uncompressed gas. Your abdomen is flexible, unlike a steel helium tank. How many PSI do you think your sphincters can withstand?