are there more doors or wheels in the world?

[Daniel-san]

Doors turn on hinges. Is a hinge a wheel?

[origami_itto]

Doors turn on hinges. Is a hinge a wheel?

They're both applications of "the lever". The hinge is synonymous with fulcrum and a wheels axle.

Or is the hinge just a part of the door, like the knob? Do we need to consider the most complex example or the most fundamental.

A door may make use of a hinge and lever but I submit a door need not be movable to be functional.

Leaving aside the entire multiverse of conceptual doors and gates