stupid physics questions

[Absolute_Zero]

Seeing as this has become, by default, the physics thread.

If the following stands and is shown to be exploitably practical, then it could become revolutionary for electron-ics... or rather, Weyltronics.

Weyl Fermions Found, a Quasiparticle That Acts Like a Massless Electron

What is a Weyl fermion?

[toxibunny]

here's a question for the smartypantses here: what is the speed of a fart? I'm talking about detectable, by nose, the fart of someone 15 feet away. indoors. how quickly can it be done?

[pogo]

I don’t think it has a speed once it leaves the body. For one the person who smells it is often the one who does it, which suggests it goes nowhere, just rises as warm air, much of the time. So the answer is basically whatever the airspeed is. Outside that might be the windspeed, and whoever is downwind would smell it. Indoors it will depend on air conditioning, drafts, and other normal sources of air movement.

[k345y]

I don’t think it has a speed once it leaves the body. For one the person who smells it is often the one who does it, which suggests it goes nowhere, just rises as warm air, much of the time. So the answer is basically whatever the airspeed is. Outside that might be the windspeed, and whoever is downwind would smell it. Indoors it will depend on air conditioning, drafts, and other normal sources of air movement.

You didn't factor the vital.
It does have a speed once it has been released, some farts are a matter of slow permeating seepage as you suggest but many more are launched with a high pressure and velocity which will factor into the over all from ass to nose equation.

[toxibunny]

gas molecules ping about though...

[k345y]

gas molecules ping about though...

But at the same time conform to their predicted trajectories.

Leave the exhaustive by product quantum mechanics to the physicists and trust in your natural given ability to sense the incoming direction of farts.

[gumboot]

HTH

[t0ne]

On a related note, it takes my dog about 2 seconds to detect if you get cheese out of the fridge. From the next room. We've been trying to work out how he can tell it's cheese and not something else other than by the smell?

[zip accident]

On a related note, it takes my dog about 2 seconds to detect if you get cheese out of the fridge. From the next room. We've been trying to work out how he can tell it's cheese and not something else other than by the smell?

I googled speed of diffusion, didn't get anything that wasn't long equations, I think it's of the order of feet or maybe metres per second, but it varies depending on the substances, two seconds for five or ten metres seems too fast, maybe the wrapping makes a distinctive sound?.

[gumboot]

Yeah, it's not just doggy noses that put humans to shame. It's their ears too. And also their eyes in some respects.

.. and even their buttholes. Apparently if you're lost in the jungle you can figure out which way's north by the way your dog poops. Thanks wikipedia!

[pogo]

Sound seems much more likely. Cheese hardly smells when cold, and as much as it does then opening the fridge door will let out the smell. Not only could he be hearing the particular packaging but maybe what you say: dogs can’t understand language but can recognise particular words.

[t0ne]

We've thought it must be sound but it would have to be a very subtle difference as a lot of stuff is packaged very similarly or just wrapped in clingfilm and he only does this with cheese.
I started to think about the phenomenon where dogs can apparently know when their owners are leaving work etc. perhaps he picks up on me thinking 'mmmmm cheeeese'?

[pogo]

It may be a subtle difference to you but dogs hearing works quite differently. They can hear sounds we can’t, such as the frequencies of a dog whistle, which will mean they hear additional harmonics which may help them. They also have better directional sense, and brains tuned to use their ears and noses more for locating sources of sound (while we rely much more on sight).

The other thing might be behavioural, in that dogs are very close observers of their owners, who they consider pack leaders. It may be something you do, even subconscious, that they pick up on. They can of course be trained, deliberately or not, to associate certain words or with things.

[toxibunny]

it could also be confirmation bias.

[gumboot]

So... Hindenburg... paint versus hydrogen...

Mythbusters seem to have done a scientifically insulting experiment comparing air-filled to hydrogen-filled, which raised a question for me before I actually saw it and decided that that just made the debate even stupider.

But the question is, does the rapid, upward escape of a lighter-than-air gas, even if it's not flammable, cause an inrush of air (containing oxygen) which literally fans the flames of the other burning materials? Contrasted with an air-filled balloon where the inrush of air is only that brought about by convection.