# 利用滾動實驗測量摩擦係數

2005年

## 摘要或動機

A cylinder rolling on an inclined plane and a sphere on grooved tracks are discussed in details.Using elementary mechanics, the formulas are derived for the time interval (t) and the final speed (vas a function of release height (h). (1) A cylinder is rolling down an inclined plane. The speed and time of the center of mass ofthe cylinder which changed with position (x) are recorded by a motion sensor. We can get theplots of v vs. √x and t vs. √ x, and find that the acceleration of the center of mass of thecylinder is constant, whether the cylinder is in rolling or a combination of rolling and slipping. (2) A sphere is rolling down an inclined grooved track. The final speed at the bottom of thetrack can be calculated from the physics of projection motion after the sphere leaves the track to thefloor. The time t for the sphere starting from rest to the bottom can be recorded by using photogate detectors. From the v-√h and t-1/√h graphs, μs between the sphere and track can be obtained. (3) When a sphere is released from the vertical height h of a cycloidal slide, the time tof pure rolling is the same independent of release position. But, when the sphere moves at a combination of rolling and slipping, the time t' will be different from t. We measure t and t' with photogate detectors and get the plot of t vs. h. The value ofμs can be calculated from the t - h graph. 圓柱或鋼珠從斜面或有槽曲面形成的軌道上滾下時，利用基本力學，可推導出時間 (t) 、速率 (v) 隨高度改變的函數關係。 (1) 利用運動感應器記錄圓柱由斜面上滾下時，圓柱質量中心的速度及運動時間隨位置 (x) 的變化，可繪出 v 對√ x 及 t 對 √x關係圖，由v－√x 及 t－√ x圖可知不論圓柱純滾動或滾動兼滑動，其質心均等加速度運動。 (2) 鋼珠由有槽斜板滾下時，到達底端的速率可由從底端至地面的拋體運動算出，而其時間t則可利用光電計時器直接記錄，利用 v－√h 圖及 t－1/√ h 圖可求出鋼珠和軌道的靜摩擦係數 μs。 (3) 鋼珠從旋輪線上方純滾動至底端時，所經歷的時間 (t) 和釋放高度無關，但是當鋼珠滾動兼滑動時，所經歷時間 t' 會改變，利用光電計時器量出 t 及 t'並作圖，利用 t－h 圖可出 μs。

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