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  • There’s nothing quite like hearing a fart, and knowing the painful inevitability of it

  • crossing your nose’s path. But, if you could react quickly enough, do you even stand a

  • chance to escape it’s smell? Could you outrun a fart?

  • If youre trying to outrun the sound...good luck! Sounds are vibrations that travel through

  • particles in a wave, and their speed is dependent on the medium theyre travelling in. For

  • example, sound travels 4x faster in water than air, because the particles are much closer

  • together, meaning they more quickly transmit vibration energy. When travelling through

  • air at sea level and 15℃, sound travels at 340 m/s - way faster than the fastest man

  • on earth, Usain Bolt, who can only move 12.4 m/s. Not even the fastest animal, the

  • peregrine falcon which can travel 82 m/s - could soar past the sound of it’s own toot.

  • But it’s the smell that most are concerned about escaping anyway, and here’s where

  • it gets a bit more complicated. Unlike sound waves and visible light which travel through

  • the air, smell is made up of the odour compounds that create the air. When you cut the cheese,

  • odor molecules travel through the air and up your nose where they bind to odorant receptors.

  • And each individual has a unique set of receptors, meaning we all perceive smell differently.

  • At the basic level, smells travel through the process of diffusion whereby particles

  • move from area of high concentration to low concentration, until reaching a state of equilibrium.

  • But the composition of every fart is unique, based on the food you ate, your gut bacteria

  • breaking it down, and the swallowed air you took in. Yup - farts are like snowflakes;

  • each with it’s own variance. But the average fart tends to be composed of 59% nitrogen,

  • 21% hydrogen, 9% carbon dioxide, 7% methane, 3% oxygen, and only around 1% is made up of

  • the smelly stuff. Even knowing this, we would still need to know the concentration at the

  • source, the temperature, air pressure, and wind movement in the room - which even in

  • a very still room is significant. Anecdotal evidence on the internet suggests that farts

  • are ejected at about 3 m/s, but there is little scientific evidence to back this up.

  • However, if we take into account the temperature of the gas, pressure and kinetic energy of

  • molecules, then the kinetic theory of gasses can help predict the average speed of a gas

  • molecule. But since a fart is made up of many molecules, let’s just focus on one of the

  • smellier parts: skatole. If we use the kinetic theory of gasses, assume that the fart is

  • at body temperature, and then we plug in the molar mass of skatole, we calculate that the

  • smelly skatole may be travelling around 243 m/s! Which is obviously faster than a human

  • can move.

  • Of course, these molecules aren’t travelling in an uninterrupted line but are constantly

  • colliding into other air particles and physical matter. As a result the gas cloud as a whole

  • travels much slower still guided by diffusion. And it doesn’t take into account any air

  • movement like wind or the ejection direction, which could either work for or against you.

  • So, while you certainly can’t run faster than the absolute speed of smelly fart particles,

  • with a little luck, you might be able avoid the fart itself!

  • Want more fart science? Check out our videosAre Silent Farts More Deadly?” andWhy

  • Do We Like Our Own Farts?” By clicking the screen or using the link in the description.

  • And subscribe for more weekly science videos!

There’s nothing quite like hearing a fart, and knowing the painful inevitability of it

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B2 US fart air outrun travelling kinetic smelly

Could You Outrun A Fart?

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    Jack Lu posted on 2016/04/29
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