Experimental Test of Time Scales in Flowing Sand

We describe dynamic measurements of the stress obtained during a sand flow. The data show a large noise component as seen in power spectra for these data which satisfy P = P 0 ω -α over at least three decades. Values of α span 1.3 ⩽ α ⩽ 2.3. A calculation of the Hurst parameter of fractional Brownian motion yields values of H which satisfy α = 2 H + 1 within statistical errors. A time scale predicted from continuum models of sand flow may be present, but the inherent noise makes this scale difficult to determine.