人教版高中物理必修第一册2.4 自由落体运动 课件PPT

自由落体运动三门第二高级中学高中物理必修（Ⅰ）第二章第四节主讲：刘保才 探究过程一——自由落体运动问题：重物体比轻物体下落快吗?实验器材：不同硬币、纸片 实验探究实验１:将一枚硬币和一张展开的纸片从同一高度自由下落实验２：把一张纸片捏成纸团，将纸团和一张展开的纸片从同一高度自由下落实验３：将一枚硬币和一枚表面贴有纸片的硬币从同一高度自由落下 铁球和轻的铁球下落快慢相同实验演示 如果物体只受重力作用(空气阻力可忽略不计时)，在同一高度静止释放不同物体,它们下落的快慢应该相同，而与物体轻重无关结论： 自由落体运动定义：物体只在重力作用下从静止开始下落的运动，叫做自由落体运动注意：在有空气的空间里，如物体重力远远大于所受空气阻力，此阻力可忽略不计，则物体下落的运动也可看作自由落体运动 探究过程二——运动性质轨迹——运动特征——加速?匀加速?直线 检验猜想根据频闪照片记录的各时刻小球位置，可直接判定轨迹为直线根据小球在不同时间里下落的位移的规律可判定是否是匀变速直线运动用给出的自由落体运动的频闪照相图片(频闪时间间隔为1/25s) 分组分析实验分析频闪照片小球的运动轨迹由频闪照片读取小球在不同时间里距初始位置的位移根据所给公式计算a 实验结果用直尺判定小球的运动轨迹匀加速直线运动！加速度a的值 结论自由落体运动是初速度为零的匀加速直线运动同一地点一切物体下落的加速度都相同，方向竖直向下,这个加速度叫做自由落体加速度，也叫做重力加速度，通常用g表示 地点纬度重力加速(m·s-2)特点赤道0°9.780最小广州23°06′9.788武汉30°33′9.794上海31°12′9.794东京35°43′9.798北京39°56′9.801纽约40°40′9.803莫斯科55°45′9.816北极90°9.832最大 基本公式:V=gtH=gt2例1：屋檐上水滴下落的过程可以近似地看作是自由落体运动。假定水滴从10m高的屋檐上无初速滴落，水滴下落到地面时的时间大约是多少？速度是多少？ 例2：一块自由下落的小石头，经过某点时的速度是9.8m/s,经过另一点时的速度是39.2m／s,求这两点间的距离和经过这段距离所用的时间。 自由落体运动的实际应用（一）测反应时间用一长米尺，记录下落位移，根据自由落体运动规律和已知的g值来计算反应时间t 如何测反应时间 自由落体运动的实际应用（二）如何测量悬崖、峡谷的高度测高度 小结自由落体加速度(重力加速度)自由落体运动的规律自由落体运动规律的实际应用作业:课本P47(2)(3)自由落体运动的概念 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