Computer Measurement of Nonlinear Characteristics of Physical Pendulum Driven by an Externally Applied Force

自作の物理振子を用いて，強制振動のコンピュータ計測を行った。軸の摩擦を軽減するために，軸の両端にボールベアリングを使用し，木板の振子と軸が一体となって振動するように作成し，共軸にポテンショメータを取り付けて，角変位を電圧に変換し，外部励振の周期を徐々に自動掃引しながら，一連のデータをコンピュータで測定した。非線型振動特有の振幅飛躍現象と履歴現象が得られた。強制振動の運動方程式を数値的に解き，実験との比較を行った。コンピュータを活用した物理実験教材開発の一例となる。An experiment about the nonlinear forced oscillation of a physical pendulum is investigated with a computer.The pendulum can swing about the horizontal axis which is supported by two ball bearings at both the ends,and the instantaneous angular displacement of the pendulum is measured as digital data by a potentiometer mounted coaxially.The system is driven by an externally applied sinusoidal force.The experiment clearly revealed two distinct nonlinear phenomena one a phenomenon of discontinuous jumps in the amplitude of oscillation as a function of the period of the driving force,the other a phenomenon of hysteresis loop in the amplitudeperiod curve:when the period of external force is increased and when the same is decreased the discontinuous jumps in the amplitude take place at different periods of the external force.The motions of the physical pendulum are also numerically analysed by means of computer simulations