A single unit impact absorber is a ball absorber located in a mechanical system to attenuate its undesirable vibration. The absorber has a free motion constrained by stops. Collisions between the main system and the absorber masses help to dissipate kinetic energy as heat, noise and high frequency vibrations and thus reducing the main system dynamic response. However, the collisions give rise to discontinuity and strong nonlinearity. This work intends to study the effect of the collision modeling on the absorber efficiency. The contact force-based linear viscoelastic model of Hook-Newton, nonlinear elastic model of Hertz, and nonlinear viscoelastic model proposed by Hunt and Crossley are considered. For each case, analytical study is conducted to determine the equations of motion. The system responses are obtained for forced vibration, considering the whole ball motion cycle: left impact-free motion-right impact and following a numerical resolution based on the Newmark method. Finally, comparison of different impact models is made to conclude on the single unit impact absorber performance.