Pumice Impact Test (Side View)
High-speed digital sequence of a vertical impact by a copper sphere traveling at 4.5 km/sec into porous pumice (density of about 1g/cc).
A side-view of a near-vertical impact at 500 frames per second (or 2 milliseconds between each frame) taken with a high-speed video. This is a 60-degree impact (from horizontal) into a highly porous target of fine particles. Now you can see the funnel-shaped ejecta curtain moving across the surface after the crater forms. The curtain resembles an inclined wall of particles that actually represent the collection of particles ejected at a well-defined position, time, and velocity. Eventually the crater emerges from behind the ejecta curtain as it moves outward and becomes transparent. This sequence illustrates the evolution of a crater that is stopped by the effects of gravity, rather than strength in the target. These ejecta are launched out of the target and only gravity limits how far they can travel beyond the rim on ballistic trajectories. If the target had strength, the curtain would seem to separate from the rim as the crater finishes.
NASA Ames Vertical Gun Range, NASA Ames Research Center
Peter H. Schultz, Brown University