Measuring the Granular Density of Modes in 3D

Sand covering the earth, snow on a mountainside, and even plastic balls in a ball pit are all considered granular materials. These athermal materials, while ubiquitous, behave in a unique manner. For instance, granular materials have the ability to behave like all three phases of matter; sand in a sandstorm behaves like a gas, whereas sand flowing in an hourglass behaves like a liquid, and packed sand on a beach behaves like a solid. The solid/liquid transition is known as the jamming transition. This study will experimentally measure the granular density of modes, which is analogous to the density of states in a thermal system. In order to measure the granular density of modes, we need to mimic the randomized motion of thermal particles. We accomplish this using a white noise acoustic wave to vibrate the particles of the granular material allowing us to measure the density of modes using methods from thermal physics. From our measurement of the granular density of modes, we are able to study the jamming transition in a 3D granular material; since, as the jamming transition is approached, there is an excess number of low frequency modes in the density of modes.