2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/186366We study the dynamics of extended test bodies in flat Friedmann-Robertson-Walker spacetimes. It is shown that such objects can usually alter their inertial mass, spin, and center-of-mass trajectory purely through the use of internal deformations. Many of these effects do not have Newtonian analogs, and exist despite the presence of conserved momenta associated with the translational and rotational symmetries of the background.14 pages, minor clarifications addedGeneral Relativity and Quantum Cosmologytext