Impact on sand and water

In this thesis we investigate the impact of a body on sand and water. When a body impacts a free surface in the inertial regime the series of events is the following: On impact material is blown away in all directions and an impact cavity forms. Due to the hydrostatic pressure from the sides the cavity will start to collapse. Close to the surface the body passes early, but the pressure is low, therefore the collapse will be slow. Deeper, the body will pass later, but the hydrostatic pressure is higher. The competition between these two time intervals will cause the collapse to eventually occur near the middle of the void. As the walls of the void hit each other at the axis of symmetry, two jets are created: One is driven straight into the air and a second jet shoots down into the enclosed bubble.