TICKING HOUR GLASSES - EXPERIMENTAL-ANALYSIS OF INTERMITTENT FLOW

Fluctuations in the flow of sand in an hour glass have been investigat ed experimentally for the case when the interaction between grains and interstitial air is important. During the active phase of the how, a plug is formed at the narrowest constriction of the hour glass. The pl ug is below the. free-fail arch defining the lower ''edge'' of the san d heap in the upper chamber. The low-density region between the plug a nd the arch defines what we call a ''bubble.'' Early during the active (how) phase, the position of the bubble is stationary, whereas later, it rises into the bulk of the sand and disappears. The position of th e arch thus oscillates with a shorter period than the one associated w ith the active-inactive phase oscillation.