Absolute and relative Frenet-Serret frames and Fermi-Walker transport

Relative Frenet-Serret 3-frames are defined along a test particle worldline with respect to a family of observers and a corresponding comoving relativ e Frenet-Serret 3-frame is introduced in the local rest space of the test p article itself The latter frame provides the tools to geometrically define a generalized centrifugal force, tied to the rotation of the relative veloc ity of the test particle with respect to the observers relative to gyro-fix ed awes in the test particle local rest space. For circular orbits in a sta tionary axisymmetric spacetime, all of these relative frames for any circul ar observers are closely related to the spacetime Frenet-Serret frame, but it is the comoving frame, which reveals the geometric interpretation of the minimal intrinsic rotation observers, which are complementary to the extre mely accelerated observers to which they reduce in the equatorial plane of rotating black hole spacetimes.