system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why does higher pressure air move to lower pressure areas?

So first off, I'm a mechanical engineer and understand as a common sense POV that compressed air, when introduced to a larger volume will decompress as the gas fills the larger container...but why? Fundamentally...why does the gas decompress to fill the larger volume?

My fiance asked me "why does the higher pressure go to the lower pressure" when I was explaining the concept of lift due to the shape of an airfoil, and I couldn't give her an answer besides "because it does"

There has to be a more detailed explanation out there right? I can't believe I went through all those years of school and can't give a better explanation and it's driving me insane.
gpt
It helps to remember that "pressure" is really just the result of air molecules bouncing off things. Higher pressure = more molecules = more bouncing.

Imagine a box with a partition in the middle, high pressure on one side and low pressure on the other. Lots of molecules are bounding off one side, fewer on the other side, and the partition feels a net force away from the high pressure side.

Now we magically remove the partition...there are air molecules heading from the low pressure to the high pressure side, and from the high pressure to the low pressure side. \*But there are more going in one direction than the other". This causes the boundary between the high and low pressure areas to move towards the low pressure side as more molecules head that way than the other. This continues until everything evens out and you have equal numbers of molecules going in all directions again.