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第4节认识简单机械第4课时讲解课件

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认识 简单机械 课时 讲解 课件
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Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 想一想想一想 工人要把钢材 木料 水泥等运 到楼上通常会怎 样做呢 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 滑 轮 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 滑轮结构 轴 轮 滑轮主要部分是能绕轴转动的轮子 是一种周边有槽 可以绕着装在 框子里的轴转动的轮子 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 你是这么做的吗 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 定滑轮 轴固定不动的滑轮 动滑轮 轴随物体一起运动的滑轮 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 使用定滑轮的特点 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 二 探究使用定滑轮的特点 实验次 数 钩码所受的 重力G N 绳子末端 拉动的方向 弹簧测力计 的示数F N 1 2 3 4 5 2水平2 2斜向下2 2竖直向下2 3竖直向下3 4竖直向下4 结论 使用定滑轮不省力 但可以改变 力的方向 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial F G 定滑轮 l1l2 0 定滑轮实质就是等臂杠杆 拉力大小始终等于重物的重力大小 3 拉力F作用点移动的距离S与 物体上升高度h的关系是 S h 结论 使用定滑轮不省 但可以改变施 力的 力 方向 F F 公式 F G S绳 h物 V绳 V物 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 护城河上的吊桥 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 探究使用动滑轮的特点 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 三 探究使用动滑轮的特点 特点 使用动滑轮能省一半力 但不可以改变施力的方向 实验次 数 钩码所受 的重力 G N 施力的 方向 弹簧测力计 的示数F N 1 2 3 2竖直向 上 1 3竖直向 上 1 5 4竖直向 上 2 2 1 F G F G S 2h Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 动滑轮也是一个变形的杠杆 请找 出它的五要素 动滑轮相当于一个动力臂是阻力 臂两倍的省力杠杆 F G l2 l1 O 公式 F 1 2 总 G G动 2 S绳 2h物 V绳 2V物 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 若拉力F沿斜上方拉 F G吗 1 2 F2 F1 G L1 L2 O F1 L1 动力臂L1减小 动力F增大 要使动滑轮省一半的力 必须使绳子沿竖直方向拉 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 如图图所示 木块块在桌面上匀速滑动动 木块块所受摩擦力4牛 则则拉力F为为 牛 若物体匀速滑动动0 2米 则则拉力方 向通过过 米 2 0 4 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 思考题 1 使用定滑轮的好处是 2 使用动滑轮的好处是 能否利用定滑轮和动滑轮的优点把它们 组合起来 使它们即省力又方便呢 能 把它们组合成滑轮组 改变用力的方向 省力 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 三 滑轮组 由一个定滑轮和一个动滑轮组成 F F F G G G 1 2 F G 1 3 F G 1 2 F G h h h S 2hS 2h S 3h S nh Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 巩固练习 1 如下图 a 所示 物体B重100N 在力F作用 下匀速上升时 F应等于 N 物体上升0 5 米 绳子拉长 米 不计摩擦 图 a F 2 如上图 b 所示 物体A重为100N 挂重物的钩 子承受的拉力是 N 人匀速拉绳子的力是 N 物体上升0 5米 绳子拉长 米 动滑轮 自重不计 图 b 100 100 50 0 5 1 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 使用滑轮组时 动滑轮被几股绳子吊起 所用力 就是重物和动滑轮总重的几分之一 即 1 n F G 思考题 在左图所示的滑轮组中 a 若动滑轮重G 不计 拉力F是多少 b 若动滑轮重G 不能忽略 那么图中 的拉力F应等于多少 G G F1 5 F G 1 5 F G G 分析 图中吊起动滑轮的绳子股数为5 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 如图所示 拉力F的大小等于 F 不计滑轮重及绳与滑轮间的摩擦 1 3 F f f N G T S2 v2 S1 v1 S1 3S2 V1 3V2 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 如图所示的滑轮组中的不计滑 轮与绳摩擦 每个滑轮重3牛 1 甲轮是什么滑轮 乙轮是 什么滑 2 若不计滑轮与绳摩擦已知 物体重12N 绳端所用拉力多 大 3 若不计滑轮与绳摩擦实际测 得绳端的拉力F 为6N 则所吊 起的物体重G 多大 4 物体被吊高0 3m 则绳 端向上拉动多少m F 乙 甲 定 动 5牛 15牛 0 9米 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 如图所示 A B两个滑轮中 A是 滑轮 B是 滑轮 在不考虑滑轮摩擦和重力情况下物体与桌 面的摩擦力为90牛 匀速移动物体0 5米 水平力F 为 牛 绳子伸长 米 F A B 定 动 30 1 5
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