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    • 【教学设计】《声音的产生与传播》
    • 来源:教导处 |作者:陈虹|2019/10/9 8:27:00|浏览次数:753
    • 一、教材分析

      在学习机械运动的基础上,本章是学生初步接触声学知识的开始。声现象是日常生活常见的现象,是人们交流信息的重要渠道。本节内容的编排顺序按照声从“源”到“接受端”的信息流来编排的。以科学探究的的形式,让学生了解声的产生、声的传播,以及声速的知识。为下一节学习《声音的特性》做知识铺垫。

      二、学情分析

      1. 知识方面:八年级学生对声现象有足够的感性认识,但缺乏上升到理论高度,教师需要充分借助学生已有的感性认识;

      2. 能力方面:学生已经初步具备观察物理现象,应用物理知识解释现象的能力,但各方面能力发展还稍显不足,需逐步继续培养学生善于观察、勤于思考的能力,锻炼学生提出问题、解决问题的能力。

      三、教学目标

      1. 通过感受声带振动、音叉发声,知道声音是由物体振动产生的;

      2. 通过真空罩实验知道声音的传播需要介质,真空不能传声;

      3. 通过阅读课本小资料知道声音在不同介质中的传播速度不同,空气中声音传播的速度大约是340 m/s

      4. 知道回声现象以及人类利用回声现象的事例。

      四、教学重难点

      1. 重点:学生对声音的产生与传播过程的探究;

      2. 难点:1)设计实验探究声音的产生与传播过程;

      2)真空不能传声的实验过程、现象分析、推理方法。

      五、教学方法及仪器

      1. 教学方法:讲授法、演示法、学生实验;

      2. 教学仪器:音叉、乒乓球、水、手机、防水袋。

      六、教学过程

      教学活动

      设计意图

      【导入新课】

      教师活动:播放一首动听的音乐。

      提问:同学们喜欢音吗?

      教师活动:同学们有办法制造出声音吗?小组讨论方法,并将讨论结果大致分类。

      学生活动:讨论、交流,并给出方案。

      教师活动:提问:我们听到声音需要哪些条件?

      渗透三个条件:声音的产生、声音的传播、健全的听觉系统。

      通过播放音乐,激发学生的学习兴趣。

      【讲授新课】

      1.声音的产生

      教师活动:提出活动内容:让同学们将两只手指轻轻地放在喉部,齐声朗读“声音的产生与传播”。仔细体会后,回答问题:

      1.你在说话的时候,是否感觉到喉部在振动?

      2.你知道是什么物体在振动吗?

      学生活动:齐声朗读“声音的产生与传播”,回答教师提出的问题。

      教师活动:让学生利用课桌的器材产生声音,并仔细观察它们发声时各有什么特点?

      学生活动:小组交流讨论。

      演示实验一:音叉振动发声

      教师活动:提问:音叉发声时,我们能否清晰地观察到音叉的振动? 

      学生活动:(1)能。(提问学生:振动幅度明显吗);(2)不能(我们有哪些方法可以使得音叉的振动现象体现得更加明显呢?)

      学生活动:思考、讨论使音叉振动得更加明显的方法。然后根据提出的方法,进行实验展示,看能否解决问题。

      教师活动:(1)利用乒乓球将音叉的振动放大,将一乒乓球靠近发声的音叉,被弹开;(2)将发声的音叉放入水杯,溅起水花。

      学生活动:认真观察、体会音叉振动放大的具体方法。

      教师活动:物体的振动,有时候不容易直接观察到,我们通过某种方式把它形象、直观地呈现出来,这种研究方法,称为转换法。呈现音叉振动,同时呈现乒乓球被弹开,水面溅起水花的图片。

      教师活动:归纳总结,经过大量科学实验证实,声音是由物体振动产生。

      板书:1. 声音是由物体的振动产生的;

      演示实验二:音叉振动停止,发声停止

      教师活动:敲击音叉,用手抓住音叉,提问:发现了什么现象?

      学生活动:仔细听声音的变化。

      教师活动:解释现象,给出结论。

      板书:2. 振动停止,发声停止;

      教师活动:给出声源概念,并板书:3. 声源:发声的物体。

      提问:人说话、音叉发声的声源分别是?

      【反馈练习一】

      1. 声音是由物体的      产生的,二胡是通过     振动发声的,笛子是通过       振动发声的。

      2.正在响的鼓的鼓面用手一按,响声立刻消失,是什么原因?

      通过问题培养学生物理学科核心素养“实验探究”这一素养,着重培养学生提出猜想与设计实验、进行实验的能力, 同时充分培养学生的高阶思维,提高其分析、综合能力。

       

       

       

       

       

       

       

       

       

       

       

       

      转换法这一研究方法的渗透,既完成了知识概念的传授,又完成了方法的教学。

       

       

       

       

       

       

       

       

       

       

      渗透概念,强化概念,并充分利用刚做的实验,达到及时巩固的效果。

      过渡

      总结声音的产生相关知识,并自然过渡到声音的传播。

      2.声音的传播

      教师活动:提问:能否听到老师的说话声,老师能否听到你们的说话声,我们之间隔着空气,以此自然过渡声音能在空气中传播。

      教师活动:【思考1】声音在空气中是怎样传播的?呈现敲鼓图片。讲解鼓面的振动带动周围的空气振动,形成了疏密相间的波动,空气疏密相间的传播形成声波。

       

       

       

       

       

       

       

       

      1   声波

      教师活动:给出声波概念,并给出声波与水波对比图,板书:1.方式:声音以波的形式传播着,我们把它叫声波。

       

       

       

       

       

       

       

      2   水波

      教师活动:提问:物质的状态共有三种,分别是?既然声音能在空气中传播,那能否在液体固体中传播?

      【探究1】声音能通过固体或液体传播吗?

      学生活动:小组讨论,给出事例。

      教师活动:讲解桌子传声,并总结固体传声效果好于气体。

      演示实验三:手机音乐在水中传播

      教师活动:完成演示实验,并要求学生仔细观察并倾听声音。提问:为什么声音变小了?给出前提,液体传声好于气体,之所以声音变小了,是因为我们听到声音经历了声音从水到空气,再到人耳,发生了声音的反射,部分声音没有进入人耳。

      板书:2.条件:声音的传播需要介质。

      (气体、固体、气液体都称为介质)

      【思考2】声音离开介质还能传播吗?即声音能否在真空中传播?

      演示实验四:真空罩中的闹钟

      教师活动:将正在发声的闹钟放入抽气盘中,盖上玻璃罩,打开真空泵,开始抽气,让学生观察发生的物理现象。

      学生活动:观察现象,总结结论,真空不能传声。

      教师活动:板书:真空不能传声。

      反馈练习二

      1.水中的鱼会被岸上人的说话声吓跑,这是因为声音先经过     传播到水中,后经过    传播而被鱼听到。

      2.通常人们称月球是无声的,其原因是月球表面没有     ,宇航员在月球上要靠无线电联系,那是因为     不能传声。

      通过说话这一日常生活随处可见事例,让学生充分体会“从生活走向物理 从物理走向生活”这一基本课程理念。

       

       

       

       

       

       

       

       

      类比法的渗透,帮助学生更好、更形象地理解声波这一抽象概念。

       

       

       

       

       

       

       

       

       

       

       

       

       

      演示实验三,手机放入水中,能够极大地激发学生的学习热情与兴趣。

       

       

       

       

       

       

      真空罩实验切实为学生提供真空环境,让学生切实感受到真空不能传声。

      过渡:

      播放回声视频,让学生在了解了声音传播方式以及传播条件后,进一步深入了解声音传播的其他知识。

      3.声速

      教师活动:播放回声视频,引导学生思考,听到回声需要时间,说明声音传播是需要时间的。给出声速的概念,并说明其大小等于声在每秒内传播的距离。

      教师活动:给出课本小资料,一些介质中的声速,并提问学生发现了什么?

      学生活动:小组讨论分析有什么发现。总结声速的大小与介质的种类、介质的温度有关。一般情况下,声音在固体中的传播速度大于液体,大于气体。

      教师活动:强调一个需要重点记忆的知识:15℃时,空气中的声速约为340 m/s,并板书。

      给出回声概念,讲解人耳区分回声的前提,需要原生与回声之间间隔0.1秒,并强调人耳区别一切不同声音的前提也都是间隔0.1秒以上。

      教师活动:引导学生计算听到回声的最短距离。

      学生活动:小组讨论,进规范书写计算步骤。

      教师活动:给出结论,人耳听到回声的最短时间为0.1秒,最短距离为17米。

      反馈练习三

      学校举行运动会时,小明被安排在终点做计时员。老师告诉他:按表时要看发令枪冒出的白烟,而不能等听到发令枪响再按表。你知道这是为什么吗?

      如果听到发令枪响才开始计时,晚了多少时间?(假定当时的气温是15℃左右)

      通过课本小资料自主阅读,让学生自主思考,发现规律,培养学生的物理核心素养的物理思维。

       

       

       

       

       

       

       

       

       

      通过最短距离的计算,加深学生对回声的认识。

      过渡

      总结声音的传播与声速的相关知识。                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 

      【课堂总结】

      以“本节课你收获了什么?”这一问题,引导学生完成对本节课的重新梳理,得到课堂总结的目的。

      【板书设计】

      声音的产生与传播

      一、声音的产生

      1. 声音是由物体的振动产生的;

      2. 振动停止,发声停止;

      3. 声源:发声的物体。

      二、声音的传播

      1. 方式:声波

      2. 条件:声音的传播需要介质。

      (气体、固体、气液体都称为介质)

      真空不能传声。

      3. 声速  15℃时,空气中的声速约为 340 m/s

      4. 回声:声音的反射。

      【课堂小测】

      1. 考试时,考生翻动试卷时发出的声音是由试卷     产生的,这声音通过     传入监控老师的耳朵。

      2. 小明对着山崖大喊一声,经过2s后听到回声,那么小明和山崖之间的距离大约是多少米。

       

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