When a solid projectile strikes a granular layer, the impact forms a crater.
This impact cratering phenomenon is basically simple. It can be described as
a one dimensional motion, and the underlying physics is only classical
mechanics. Nonetheless, a lot of dissipative macro grains, granular media,
bring intriguing features to such a simple phenomenon. Surprisingly, nobody
exactly knows how a projectile stops in a granular layer, even in terms of
phenomenology. Some candidates of the force model have been proposed
recently. To clarify which one is the best at describing a wide range
granular impacts, we are measuring the velocity of the impact and discussing
its dynamics.