- if you fart you gain weight!
I can prove that:
The density of air (N2 mixture with O2) is 1293 kg/m³ and of methane (CH4) 656 kg/m³. Your fart is a mixture of both, thus it's density is lower than that of air thus your fart will rise up into the air. Therefor when you haven't farted yet, there is a lifting force in your body, lowering your weight.
An analogy is that when you carry 50 helium balloon, you'll weigh less than when you release the balloons.
For the people who prefer math:
Because you're fart raises, its acceleration is in the opposite direction of your weight. Your weight is then mass* acceleration - mass(fart)*acceleration(fart).
This theory applies on earth in a non vacuum environment.
It was to entertaining not to post this and yes I thought of all this by myself, however I can't believe that I would be the first to prove this, somewhere on the net it's probably already proven
.