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ABCDEF7 · M
Most smells consist of relatively few (probably fewer than 1 in 1000) molecules mixed in with air molecules, and the spread of the smell is largely governed by the draughts and convection currents which the air would experience even without the odour molecules.
In still air the odour molecules will spread by diffusion, that is by the speeds (usually several hundred metres per second) that they naturally possess at a given temperature; but they travel only very short distances before encountering collisions with air molecules, so diffusion is at far lower speeds.
If the smelling stuff is locally a major air component, affecting air density, then it depends on the overall mean effective molar mass. As gas density, if taken as an ideal gas, is ρ=pMRT. A dense gas would flow down and vice versa. Near all smelling stuff would be denser than air, with few exceptions like ammonia or hydrogen fluoride or methane (smelling if scented as NG).
If it is just a trace addition to air, changed air density does not play any role. Therefore, the direction of smell spreading depends on already existing air convection, either thermal or forced.
If both effects are in place then the result is subject of vector addition of both effects.
Aside of both ways of macroscopic convection, there is omnidirectional gas diffusion according to the concentration gradient.
Source: [i]https://physics.stackexchange.com/questions/687498/does-indoor-odor-smell-travel-up-or-down[/i]
In still air the odour molecules will spread by diffusion, that is by the speeds (usually several hundred metres per second) that they naturally possess at a given temperature; but they travel only very short distances before encountering collisions with air molecules, so diffusion is at far lower speeds.
If the smelling stuff is locally a major air component, affecting air density, then it depends on the overall mean effective molar mass. As gas density, if taken as an ideal gas, is ρ=pMRT. A dense gas would flow down and vice versa. Near all smelling stuff would be denser than air, with few exceptions like ammonia or hydrogen fluoride or methane (smelling if scented as NG).
If it is just a trace addition to air, changed air density does not play any role. Therefore, the direction of smell spreading depends on already existing air convection, either thermal or forced.
If both effects are in place then the result is subject of vector addition of both effects.
Aside of both ways of macroscopic convection, there is omnidirectional gas diffusion according to the concentration gradient.
Source: [i]https://physics.stackexchange.com/questions/687498/does-indoor-odor-smell-travel-up-or-down[/i]
lacrossegirl25 · 22-25, F
Reflection2 · 41-45, M