Obviously, for any polygon we can define at least $3$ different centroids:
$C1:\;$ mass center of the lamina;
$C2:\;$ mass center of vertices with equal masses;
$C3:\;$ mass center of the perimeter.
For the triangle $C1 = C2 \ne C3$; for common, even convex, polygon $C1\ne C2\ne C3$:

I'm interested: are there any theorems, facts or conjectures about these points?