why when you’re driving and lower the back windows but not the front it makes that debilitating helicopter noise?

Question

why when you’re driving and lower the back windows but not the front it makes that debilitating helicopter noise?

In: 121

Answer 1

It is the same effect as the whistle you get when blowing across the top of a bottle – but because the car is bigger, the ‘note’ or frequency, is much lower.

Air flowing across the window creates a low pressure, pulling air out. Pulling air out drops the pressure inside, too, counteracting that. The air switches to flowing in through the window. That air flowing in raises the pressure, so the flow switches again, pulling the air out. The repeated switching of pressure from low to high makes a very loud, but very low frequency, sound.