Air tends to flow faster over

Over what? is there an item here? But if we're talking about an object like for example a rock if the rock was smooth on top the air would flow smoothly but if the rock was jagged and tall in some places and and short in others it wouldn't flow as smooth, Like have you ever put your hand out of the window when you were drinking down the road? And if you put it up the wind will blow your hand back but if you lay it flat the wind will blow under and over it like a charm if you but your hand into a fist it wouldn't be able to flow as smoothly