General
An early result is due to Newton; the impact depth of any projectile is the depth that a projectile will reach before stopping in a medium; in Newtonian mechanics a projectile stops when it has transferred its momentum to an equal mass of the medium. If the impactor and medium have similar density this happens at an impact depth equal to the length of the impactor.
For this simple result to be valid, the arresting medium is considered to have no integral shear strength. Note that even though the projectile has stopped, the momentum is still transferred, and in the real world spalling and similar effects can occur.
Read more about this topic: Terminal Ballistics
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