Physical Pendulum Damped by Dry Friction

Abstract In this work, pendular movement damped by dry friction was studied. Dry friction differs from viscous friction by: a) the amplitude of oscillation linearly decays, whereas in the viscous damping the oscillation decays exponentially; b) the frequency of oscillation is keeping in presence of dry friction, however, the frequency of oscillation is reduced due to damping factor in viscous case. Some experiments were performed using a wood clapboard suspended and oscillating in lateral contact with a flat plate and using a DVD suspended by an axis stuck on its edge, where the friction was in this axis. The movements were recorded an analyzed with aid of software Tracker. It was possible to obtain decay parameters and friction force in both cases. Also, viscous damping forces were calculated due to drag from the air and showed to be negligible with respect to dry friction.摘要 本研究针对受干摩擦（dry friction）阻尼的摆动运动展开了探讨。干摩擦与粘性摩擦（viscous friction）的区别如下：a）振荡振幅呈线性衰减，而粘性阻尼下的振荡振幅呈指数级衰减；b）干摩擦存在时振荡频率保持恒定，而粘性阻尼工况下振荡频率会因阻尼因子（damping factor）降低。本研究开展了两组实验：其一为悬挂的木质护墙板与平板侧向接触并发生振荡；其二为通过粘在边缘的转轴悬挂的DVD，其摩擦作用于该转轴处。运动过程均借助Tracker软件进行录制与分析，成功获取了两组实验的衰减参数与摩擦力。此外，本研究还计算了由空气阻力引发的粘性阻尼力，结果显示其相较于干摩擦可忽略不计。