  We investigate experimentally the influence of rotation on the penetration
depth of a spherical projectile impacting a granular medium. We show that a
rotational motion significantly increases the penetration depth achieved.
Moreover, we model our experimental results by modifying the frictional term of
the equation describing the penetration dynamics of an object in a granular
medium. In particular, we find that the frictional drag decreases linearly with
the velocity ratio between rotational (spin motion) and translational (falling
motion) velocities. The good agreement between our model and our experimental
measurements offers perspectives for estimating the depth that spinning
projectiles reach after impacting onto a granular ground, such as happens with
seeds dropped from aircraft or with landing probes.
