Penetration of a spinning sphere impacting a granular medium

TL;DR

This study experimentally examines how the rotation of a spherical projectile affects its penetration depth in a granular medium, revealing that spin significantly enhances penetration and can be modeled by adjusting frictional forces.

Contribution

It introduces a modified frictional model accounting for rotational motion, providing a better understanding of penetration dynamics of spinning objects in granular media.

Findings

Rotation increases penetration depth.

Frictional drag decreases linearly with velocity ratio.

Model aligns well with experimental data.

Abstract

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.