2.4 单摆 课件 -2026-2027学年高二上学期物理人教版选择性必修第一册

25 25252525252525252525252525252525252525252525252525252 第四节 525252525252525252525252525252525252525252525252525252 0 10 252525252525252525252525252525252525252525252525 52 单摆 25252S5252525252525252525252525252525252525252525 2 110 单摆 25252525252525252525252525252525252525252525252525己 25255252552525252525252525252525252525252525255 、单摆 1.定义：将一小球用细绳悬挂起来，把小球拉离最低点释放后，小球就会来回 摆动，当绳长不变、忽略空气阻力、绳长远大于小球半径时，叫单摆。 2.单摆是机械振动，平衡位置是最低点 3.绳与竖直方向最大夹角小于5时，小球做简谐运动 252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525 单摆 25252525252525 5252525252525252525252525252525252525252525252525252525252525252552 4.证明小于5°的单摆是简谐运动 一 F(n-(六 其麻很时sinO- R 252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525 3 0 单摆 10 5252552525252525252525252525252525252525252525252525252525252525252525252525252525525252525255252552 单摆振动的周期 与什么因素有关？ 0 单摆 25 5252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252552 影响单摆周期的因素？ 结论：1.单摆做简谐运动的周期与摆长有关，摆长越长，周期越大。 252525252525252525252525252525252525252cC 525252525252525252525252525252525 5 单摆 252525252525252 525252525252 52525252525252525252525252525252525252525252525529 二、做简谐运动的单摆的周期公式 1.公式：7-2r 7-g (记) 2.1叫摆长。不是绳长，而是悬挂点到球心的距离 3.g是单摆所在地的重力加速度 4.T只与1，g有关，与球的质量及振幅无关（等时性） 2525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252 6 单摆 252525252525252525252525252525252525252525252525252525252525252525252 例题1.一个摆钟从甲地拿到乙地，它的钟摆摆动加快了 及调准方法的叙述中正确的是(C) A.,将摆长适当增长 B.,将摆长适当缩短 C.翌，将摆长适当增长 D.,将摆长适当缩短 5252525252525252525252525252525252525252525252525252525252525252525252 10 25252525252525252525252525252525 29 ，则下列对此现象的分析 2525252525252S5252525252525252525 25 7 10 单摆 2525252525252525252525252525252525252525252525252525252525252525252 例题2.在同一地方，甲、乙两个单摆做振幅不同的简 示，可知甲、乙两个单摆的摆长之比为(C) A.2:3 B.3:2 C.4:9 D.9:4 乙 0.4 08.2→ts 甲 52525252525252525252525252525252525252525252525252525252525252525252 10 2525252525252525252525252525252525 52 谐运动，其振动图像如图所 2525252525252525252525252525252525 29 8 单摆 252525252529 52525252525 525252525 2525252525 05252525 例题3.如图所示，房顶上固定一根长2.5m的细线沿竖直墙壁垂到窗沿下，细线 下端系了一个小球（可视为质点）。打开窗子，让小球在垂直于窗子的竖直平面内 小幅摆动，窗上沿到房顶的高度为1.6m,不计空气阻力，g取10m/s2，则小球从 最左端运动到最右端的最短时间为(B) A.0.2 B.0.4E C.0.6s D.0.85 房顶 墙体 窗上沿 252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525 9 单摆 5252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252552 解析： B 2 B k+比0δ 2525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252 10 单摆 252525252525252 25252525252525252525252525252525252 525252525252525252525252525252525252525252552525529 三、单摆能量分析 1.小球机械能守恒。重力势能、动能相互转化 2最高、最低点列机械能守恒：世空m 3.摆长不变时，最低点速度越快，h越大，振幅越大 2525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252 11 25 25252525252525252525252525252525252525 例题4.两个相同的单摆静止于 在竖直平面内做小角度摆动， A. 252525255252525252525252525252525252 单摆 25252525252525252525252525252525 平衡位置，使摆球分别以 它们的频率与振幅分别为 252525252525252525252S2525252525 10 5252525252525252525252525252525 水平初速V1、V2(V1>V2) f,乃和A1,A2,则(C) 525252525252S525252525252525252G 29 12 10 单摆 25252525252 25252552 例题5.做简谐运动的单摆，其摆长不变，若摆球的质量增加为原来的9/4倍， 摆球经过平衡位置的速度减为原来的2/3，则单摆振动的(B) A.周期不变，振幅不变 B.周期不变，振幅变小 C.周期改变，振幅不变 D.周期改变，振幅变大 2525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252 13