[Physics] Why buoyancy is applied on centroid

Question

My book says: "The point of application of the buoyancy force is the geometric center(centroid) of the submerged part of the body, whereas the specific gravity of the fluid is constant."
But why buoyancy is applied on centroid?

Answer 1

Because otherwise it would induce a torque, i.e., a rotation. When a (pseudo)force applies to a whole body considered as solid, you can consider it as ponctual at settled at its centroid (exactly as for gravity force).