Abstarct: Abstract: The entry of objects into water is one of the fundamental yet complex phenomena in fluid dynamics and hydrodynamics, playing a crucial role in various engineering applications, including the design of watercraft, naval missiles, offshore structures, and impact-absorbing equipment in aquatic environments. A precise investigation of this phenomenon—particularly considering the surface and geometric characteristics of the entering body—provides valuable insights into hydrodynamic forces, energy transfer, and cavity stability. In this study, the dynamic behavior of smooth and grooved steel spheres upon impact with the free surface of a liquid is numerically investigated using advanced computational fluid dynamics (CFD) techniques within the COMSOL Multiphysics software. The model employs an axisymmetric approach, moving mesh, and phase field method. Simulations are conducted for spheres with smooth surfaces and with one, three, and five horizontal grooves, under both hydrophilic and hydrophobic conditions, and across various parameters such as surface tension, viscosity, and drop height. Variables such as instantaneous velocity, impact force on the sphere, and the formation and stability of the cavity are carefully monitored. The results reveal that increasing the number of grooves enhances local disturbances, leads to greater fluctuations in drag force, and alters the timing and location of cavity closure. Specific groove configurations also influence penetration paths and cavity shapes. Moreover, hydrophobic surfaces tend to produce more stable cavities and stronger splash sheets compared to hydrophilic ones. Lower surface tension increases cavity stability and delays the point of separation, while reduced viscosity decreases hydrodynamic resistance, thus accelerating cavity detachment. The combined effect of these two parameters significantly alters system behavior and modifies the impact pattern Furthermore, analysis of penetration dynamics and the distribution of forces on the sphere shows that the combination of surface features and fluid properties plays a decisive role in governing the impact process. These findings can contribute to the optimized design of water-entry bodies in scenarios requiring reduced initial impact and enhanced performance of marine structures. Future research directions include the study of non-spherical shapes and angled entries.