In superconductors, when the magnetic field has a parallel component to the current density J force-free effects appear due to flux cutting and crossing. This results in an anisotropic E(J) relation, with E being the electric field. Understanding force-free effects is interesting not only for the design of superconducting power and magnet applications but also for material characterization. This work develops and applies a fast and accurate computer modeling method based on a variational approach that can handle force-free anisotropic E(J) relations and perform fully three-dimensional (3D) calculations. We present a systematic study of force-free effects in rectangular thin films and prisms with several finite thicknesses under applied magnetic fields with arbitrary angle θ with the surface. The results are compared with the same situation with the isotropic E(J) relation. The thin film situation shows gradual critical current density penetration and a general increase of the magnitude of the magnetization with the angle θ but a minimum at the remnant state of the magnetization loop. The prism model presents current paths with 3D bending for all angles θ. The average current density over the thickness agrees very well with the thin film model except for the highest angles. The prism hysteresis loops reveal a peak after the remnant state, which is due to the parallel component of the self-magnetic-field and is implicitly neglected for thin films. The presented numerical method shows the capability to take force-free situations into account for general 3D situations with a high number of degrees of freedom. The results reveal new features of force-free effects in thin films and prisms.