Experiments on the Effect of an Irregular Successsion of Impulses upon a Simple Vibrating System

一定の固有振動週期を有する振動系に、不規則な間隔をもつて、多数の衝撃が相次いで興へられた時に、其振動系が如何なる運動をするであろうかといふ事は、地震学上に於ても興味ある問題である。此問題に就て著者のー人は、十余年前に、若干理論上の考察をして其結果を発表して置いた。今、此処では、此の問題に関する実験を行つて、前に得た理論上の結果と比較し、叉実験的模型によつて得られる運動を地震の運動等と比較して見たのである。A physical pendulum is excited into an irregular oscillation by the impact of two streams of shots impinging upon it from the opposite sides. The motion recorded is studied with respect to its mean kinetic energy as a function of the velocity and the number of the colliding shots and also of the logarithmic decrement of the pendulum. The results of experiments are compared and found approximately agreeing with those expected from the theory, in the case when the number of collision per second is small. When the number is very large some discrepancies are observed which may be explained by the increase in the effective mass as well as the effective damping of the pendulum on account of the swarm of shots surrounding the vibrating mass. It is pointed out that the general formal characters of the motion of the pendulum here studied are essentially similar to that of some or other types of motion of the earth as recorded by seismographs. An important bearing of this fact upon the fundamental problems of seismology is briefly suggested