It all comes down to chemical bonds eventually, even if they're just van der Waals forces providing a little local adhesion.
In the case of the centrifuge, it has to generate internal tension forces to maintain circular motion, because every part of a rotating system is accelerating towards the centre, and a force is required to maintain that acceleration. Even a disc of solid diamond will fail when these centripetal tension forces exceed the strength of the covalent carbon bonds.

Grant Hutchison