Abstarct: Abstract The phenomenon of solid objects impacting water surfaces has consistently been a focal point for researchers due to its wide range of industrial applications. This study employs a phenomenological approach, with a specific emphasis on the role of key variables such as object geometry, impact velocity, and density, to identify and analyze the diverse patterns of cavity formation, water splash, and total hydrodynamic force. In this research, the penetration process of cylindrical projectiles into water was experimentally investigated using high-speed imaging technology. The projectiles were designed to be completely identical in terms of net forces, dimensionless numbers, and center of mass. To achieve this, projectiles with uniform length, diameter, and material were used. The results of this study demonstrated that the internal geometry of hollow projectiles, particularly the conical shape within them, plays a pivotal role in the impact dynamics and the formation of internal jets. Furthermore, a direct and significant relationship was observed between impact velocity, effective density, and internal geometry with variables such as penetration depth, cavity closure time, and hydrodynamic forces. In the examination of hollow cylindrical projectiles, cavity closure patterns were categorized into three distinct regimes baxsed on variations in impact velocity and internal geometry. The findings indicate that divergent internal geometries, compared to other shapes, create the highest internal jet height and the largest cross-sectional area at the moment of water entry. This unique characteristic leads to the channeling of a larger volume of air into the water and increased resistance against cavity closure. Regarding solid cylindrical projectiles, changes in effective density at a constant impact velocity resulted in significant variations in the cavity closure regime, penetration depth, and separation time. Additionally, an increase in effective density led to an increase in velocity, acceleration, and the total hydrodynamic force coefficient. The findings of this research can be utilized in the design and optimization of marine and aerospace equipment. For instance, in the design of submarines, the use of conical internal geometry can significantly reduce resistive forces during motion. In emergency landing systems for space capsules or marine rescue equipment, selecting the appropriate internal geometry can reduce impact force and enhance safety. In the military domain, effective density is a determining factor in the penetration depth and stability of cylindrical torpedoes. However, limitations such as the range of impact velocity and the dimensions of the models used highlight the necessity for further research in the area of more complex geometries and diverse flow conditions.