  In this paper we develop a simple model of the penetration process of a long
rod through an uniform target. Applying the momentum and energy conservation
laws, we derive an analytical relation which shows how the penetration depth
depends upon the density of the rod, given a fixed kinetic energy. This work
was sparked off by the necessity of understanding the effectiveness of high
density penetrators (e.g. depleted uranium penetrators) as anti-tank weapons.
