Abstract:

The changing weight of the flowing hourglass is researched. The theory，from the perspective of momentum，reveals that the weight variation is proportional to the rate of change of the length of the momentum column(the region that granules flow)and the proportionality coefficient is mass flow rate. The physical image is clear，and it gives the analytic expression of changing weight. Digital measurement of weight is realized by making use of PASCO system to build a weighing platform. Burning out the rope is adopted to decrease experimental error when starting the hourglass. The theory is in good agreement with the experimental results and it shows universality under different loading quantities.

Key words: hourglass, weight, momentum