Speeding up the propeller's rotation increases its thrust, while shifting the blades' angles changes the direction of the thrust.

So, in a way, you can think of these as a space analog of polar coordinates because you just use distance to the origin, and then you have to use angles to determine in which direction you're going.

In order to study the rule of seepage flow in fissured rocks, the influence of permeability of fissures in different intersection angles and direction is compared.