Granular gases of rough spheres: Velocity, rotation and collision statistics from in-situ measurements, optical data and simulations

¹ Dept. of Engineering, Brandenburg University of Applied Science, Brandenburg an der Havel, Germany
² MARS, Otto von Guericke University Magdeburg, Magdeburg, Germany
³ MTRM, Otto von Guericke University Magdeburg, Magdeburg, Germany
⁴ Department of Physics and Applied Mathematics, Universidad de Navarra, Pamplona, Spain

Published online: 1 December 2025

Abstract

Granular gases are not only of interest in fundamental physics, but they can also serve as a test ensembles for the validity of collision models employed in (loose) granular matter. The theoretical literature mainly addresses spheres under ideal conditions and simulations allow full access to all particle parameters, but experiments cannot fulfill these idealizations. We investigate granular gases of soft, rough spheres by combining microgravity experiments and adjusted simulations. We introduce Smart Particles with embedded autarkic micro-sensors for in-situ measurements of rotation rates and accelerations. Additionally, we extract 3D positions, translations and orientations of the particles from stereoscopic video data using Machine-Learning based algorithms. We address the partition of kinetic energy between the degrees of freedom, the angular and translational velocity as well as collision statistics. A simulation is adjusted to experiment parameters, showing good agreement of translational motion, but qualitative differences in the decay of rotational kinetic energy.