Acoustic emission from crumpling paper

From magnetic systems to the crust of the earth, many physical systems that exhibit a multiplicity of metastable states emit pulses with a broad power law distribution in energy. Digital audio recordings reveal that paper being crumpled, which can be easily held in hand, is such a system. Crumpling paper both using the traditional hand method and a cylindrical geometry uncovered a powder law distribution of pulse energies spanning over two decades: p(E) = E(alpha), alpha = 1.3 - 1.6, with clearly nonexponential distribution over three decades. Crumpling initially flat sheets into a compact ball (strong crumpling), we found little or no evidence that the energy distribution varied systematically over time or the size of the sheet. When we applied repetitive small deformations (weak crumpling) to sheets which had been previously folded along a regular grid, we found no systematic dependence on the grid spacing. Our results suggest that the pulse energy depends only weakly on the size of paper regions responsible for sound production.