photoelectric door. In this paper，the self-resembled calibration system with plumb and a funnel

for point location is adopted to ensure the ball falling along the central axis of the glass

cylinder. In addition，four sets of photoelectric door are used to measure the time. This

method makes it possible to accurately find the interval of uniform falling and obtain four groups

of experimental data in a single experiment. The new measuring instrument eliminates the

disadvantages of the traditional falling-sphere method and improves the efficiency and accuracy of

experimental measurement.