Jamming: A simple introduction

Amorphous materials as diverse as foams, emulsions, colloidal suspensions and granular media can jam into a rigid, disordered state where they withstand finite shear stresses before yielding. Here we give a simple introduction to the surprising physics displayed by a very simple model system for the jamming transition: frictionless, soft spheres at zero temperature and zero shear that act through purely repulsive contact forces. This system starts to become rigid, i.e. goes through the jamming transition, whenever the confining pressure becomes positive. We highlight some of the remarkable geometrical features of the zero pressure jamming point and discuss the peculiar mechanical properties of these systems for small pressures.