Let's say I'm in a room with some kind of noxious stink, possibly of flatulent nature. The quickest way to right the world that comes to mind is to open a window. When I open a window, how do the stank particles leave the room?
[Physics] When I open a window to air out the room, how does the smell disperse
airdiffusionflowfluid dynamicsgas
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The car is behaving like a closed pipe, so you get a resonance set up. There's a Wikipedia article here, but for once the Wikipedia article isn't that great, so there's another better article here. I imagine you (like most of us) will at some point have discovered you can make a sound by blowing across the top of an opened bottle, and it's the same thing happening in your car with the open window acting like the opening in the bottle. Since your car is much bigger than a bottle the resonance frequency is uncomfortably low.
When you open a second window you get an air current flowing through the car and this destroys the resonance.
As the door nears the door frame there reaches a point where the door, for a moment, effectively seals off the air in the room from the air outside the room. This only happens for a moment, since most doors aren't 100% air proof. When this happens, as the door continues to close it decompresses the air inside the room, because the volume of the room increases as the door continues to close but the amount of air inside the room doesn't change because the room is briefly sealed off from outside the room. Thus there is an air pressure difference across the door, with the greater pressure coming from outside the room. This greater pressure slows the door down right before it closes.
On the other hand, with a window open air is let into the room and so even though the volume of the room increases as the door closes the air pressure from outside the window pushes air into the room to keep the air pressure inside the room about the same as outside. No pressure air pressure difference is found across the door and thus it does not slow down.
It is also possible that a fan or something inside the building could be creating a lower air pressure inside the building and thus there is a small air flow from the window into the building, which would push the door to close faster one the above-described brief sealing of the room happens, thus increasing the volume of the "slam!".
Best Answer
Gases diffuse from higher concentration to lower concentration because this process of diffusion increases the gas's entropy.
Every thing in the universe, in general, aims for two things : Minimum energy and maximum entropy.
Entropy is the degree of randomness of a substance. A gas in a container has low entropy because the probability of finding that gas in the universe is less but when the container is opened the gas diffuses into the atmosphere and this diffusion increases the probability of finding that gas in the universe and thus, increasing the entropy.
To move a little more into science, The Gibbs energy change of the system must be -ve in order for the process under observation (say diffusion) to be spontaneous or naturally occurring.
Here, ∆G, ∆H and ∆S are the change in the gibbs energy, enthalpy and entropy of the system respectively.
(enthalpy is the heat content of the system at constant pressure).
Now, when gas diffuse from higher concentration to lower concentration the heat change is negligible but the entropy change is highly +ve (∆S = +ve). The net result is the decrease in the gibbs energy of the system.
Therefore, Diffusion of a gas from higher concentration to lower concentration is a spontaneous or naturally occurring process.