How close together must air molecules be to bounce off one another?
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When, say N2N2, is in the wild, it regularly collides with other N2N2.
I assume these collisions happen as, having become sufficiently close, the atomic electrons are repelled from the other molecule's electrons, setting up two dipoles (whose dipole moments are in opposite directions, so repel). I conjecture the ||dipole moment|| ∝r−3∝r−3, the situation being somewhat analogous to the tidal effect.
TL;DR:
Regardless, there is some effective volume that the molecules take up such that, if one molecule wanders into another's effective volume, its path is considerably perturbed*. How does one calculate it, especially for diatomic molecules? Is N2N2's effective volume in collisions with N2N2 noticeably different from its collisions with O2O2?
*I feel I should clarify 'considerably'. I suppose a reasonable definition would be that if two N2N2molecules are travelling in opposite directions along parallel lines dd apart, they are considerably perturbed if the angle θθ that they are both thrown off their original line by satisfies θ<π100θ<π100. Note that if d≫d≫ the bond lengths, then the effective volume is essentially spherical and so θθ will not be a function of the molecules' orientations, only of dd.
If anyone's interested, I'm interested in this to work out particles' mean free paths in air.
I assume these collisions happen as, having become sufficiently close, the atomic electrons are repelled from the other molecule's electrons, setting up two dipoles (whose dipole moments are in opposite directions, so repel). I conjecture the ||dipole moment|| ∝r−3∝r−3, the situation being somewhat analogous to the tidal effect.
TL;DR:
Regardless, there is some effective volume that the molecules take up such that, if one molecule wanders into another's effective volume, its path is considerably perturbed*. How does one calculate it, especially for diatomic molecules? Is N2N2's effective volume in collisions with N2N2 noticeably different from its collisions with O2O2?
*I feel I should clarify 'considerably'. I suppose a reasonable definition would be that if two N2N2molecules are travelling in opposite directions along parallel lines dd apart, they are considerably perturbed if the angle θθ that they are both thrown off their original line by satisfies θ<π100θ<π100. Note that if d≫d≫ the bond lengths, then the effective volume is essentially spherical and so θθ will not be a function of the molecules' orientations, only of dd.
If anyone's interested, I'm interested in this to work out particles' mean free paths in air.
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If you drop a ball, it bounces a bunch of times, but the height of each bounce gets shorter and shorter. Because it loses energy in each bounce.
So I don't see how a pressurized gas doesn't lose energy. As I understand it, pressure is a manifestation of lots of molecules bouncing off each other. So over time, shouldn't the pressure drop as the molecules lose speed? and eventually all the molecules will settle in a pile on the floor.
I think another way to phrase this is, how do elastic collisions not lose any energy in the exchange? My understanding of the 2nd law of thermodynamics is that some energy is always "lost" when it's converted from one form to another, or transferred from one object to another. I.e., no transfer/conversion of energy is ever 100% efficient.
So I don't see how a pressurized gas doesn't lose energy. As I understand it, pressure is a manifestation of lots of molecules bouncing off each other. So over time, shouldn't the pressure drop as the molecules lose speed? and eventually all the molecules will settle in a pile on the floor.
I think another way to phrase this is, how do elastic collisions not lose any energy in the exchange? My understanding of the 2nd law of thermodynamics is that some energy is always "lost" when it's converted from one form to another, or transferred from one object to another. I.e., no transfer/conversion of energy is ever 100% efficient.
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