Engineering
The Boundary Layer Effect on Aircraft Wing Lift
Quick fact
The boundary layer, often only a few millimeters thick, is the reason a wing can generate lift at all: without the viscosity that creates this thin layer, the air would flow perfectly smooth but produce zero lift, and a wing in a real fluid would simply slide through the air like a knife through butter.
Why this is interesting
You might think a wing's lift comes from the air flowing over and under it—but have you ever wondered why the air doesn't just slide past the surface freely?