system
Given the following post, respond as if you're commenting on Reddit:
human
ELi5: Why is the wind so loud when you drive fast and have the windows open?
gpt
The air in our atmosphere is made up of extremely small molecules of nitrogen (\~78%), oxygen (\~21%), and trace amounts of other gases like carbon dioxide, argon, water, etc. When you are driving fast, the car is hitting all these molecules and those collisions create many small vibrations which is what our ears sense and our brain interprets as sound.

Cars are fairly sound proof when the doors and windows are closed so you don't hear the collisions outside the car very well. When you open a window though, these millions and billions of molecules enter your car's interior and collide with things inside the car. With no sound barrier between you and the vibrations from collision, you can easily pick up the sound.

The loudness of this sound is also correlated to how fast you are driving. This is because the speed that your car hits the air molecules affects how strong the collisions are. That's why driving in a neighborhood is much more quiet than driving on the highway.

Now this isn't technically the same as "wind" because it's sort of the opposite cause, even if it still has the same effect. When wind hits you it is also loud for the same reason, the molecules hit your head and ears and you pick up the vibrations from these collisions. But in the case of wind, the air molecules are what's moving fast and hitting you whereas when you drive, you are the one moving fast and hitting the air. It's a small difference and depends on how you define wind, but they both sound the same cause it is just the vibrations from the collisions you hear.