声现象复习知识点讲义.pdf

专业好文档第 1 页 共 11 页第二章声现象第二章声现象一、声音的产生一、声音的产生声音是由于发声体的振动产生的。（1）一切发声的物体都在在振动。声源：能够发声的物体。声源既可以是固体，也可以是液体或气体。（2）振动一定会发声，但发出的声音人不一定会听到（如果物体不振动，是决不会发出声音的）（3）振动停止，发声也停止。注意：注意：“振动停止，发声也停止”是指当发声的物体停止振动时，发声体将停止发声，但原来发出的声音仍在介质中继续传播，直至消失，所以不能理解为“振动停止，声音消失”。二、声音的传播二、声音的传播（1）声音的传播需要介质。真空不能传声，因为没有传播声音的介质。（2）介质：声传播所需要的物质，介质可以是固体、液体或气体。（3）声波：声以波的形式在介质中传播。注意：注意：一般情况下，我们听到的声音是由空气传播的，传播的具体过程是:物体的振动引起周围空气的振动，形成声波，以声波的形式向外传播，被人耳接受，人就听到了声音。在真空状态下，因为发生声体周围没有介质，无法形成声波，因此不能将振动向外传播，也就不能传声。专业好文档第 2 页 共 11 页三、声速三、声速（1）声速：声音在介质中传播的速度叫声速，它的大小等于声音在每秒内传播的距离，单位 m/s，读作：米每秒。（2）影响因素：声音的传播速度与介质的种类和温度有关。（3）规律：声音在不同介质中传播的速度不同，原因是：介质不同，其传播声音的性质、方式也不同。声音在固体中传播最快，其次是液体，空气中的传播速度最慢;同一种介质，当它温度改变时，传播声音的速度也有差异。（4）大小：15，声音在空气中的传播速度为 340m/s.四、回声四、回声（1）形成：声音在传播过程中遇到较小的障碍物会绕过去，遇到较大的障碍物，会反射回来形成回声。（2）人耳听到回声的条件：人耳分清前后两个声音的时间间隔至少为 0.1s,如果时间差少于 0.1s，人耳就无法辨别出回声与原声，此时回声和原声混合在一起，起到加强原声的作用，声音听起来变得响亮。因此在一般条件下，我们距离障碍物至少 17m 才能听到声音。（3）应用：可以利用回声册距离，如测海底的深度等等。在利用回声现象求距声源的距离 s=vt/2，v 表示声速，t 表示时间。知识拓展：知识拓展：不同的障碍物吸收声波的能力不同。通常，松软多孔的表面吸收声波的能力强。如果障碍物对声音的吸收作用强，可以减弱回声。例如，在剧场，特别是在录音场所，为了增强原声的效果，专业好文档第 3 页 共 11 页会在场所内加设布制屏障吸收声音。在坐满人的教室里讲话，回声不明显的原因之一是原声被吸收，回声较小。五、我们怎样听到声音五、我们怎样听到声音1.人耳的构造2.骨传导（1）人耳感知声音的途径：空气传声和骨传声。（2）骨传声：声音通过头骨、颌骨也能传到听觉神经，引起听觉，叫做骨传导。3人听到声音的条件人耳听到声音必须具备三个条件：声源、介质和良好的听觉器官。人耳听到声音的过程：发声体因振动而发出声音，并以声波的形式向远处传播；声波传到耳中，引起鼓膜振动；再经过其他组织刺激听声源头骨、颌骨空气震动鼓膜振动听小骨、半规管、前庭听觉神经听觉神经专业好文档第 4 页 共 11 页觉神经，听觉神经把这种信号传递给大脑，就产生了听觉。4.双耳效应和立体声（1）概念：同意声源到两只耳朵的距离往往是不相等的，这样就会造成声音到达两只耳朵的时间、强弱不同，人就是根据两只耳朵所听到声音的这些差异，确定出声音传来的方位这就是双耳效应。（2）原因：对同一声音，两只耳朵感受到的强度不同；同一声音，1 2两只耳朵感受到的时间不同；同一声音，两只耳朵感受到振动的 3步调不同。（3）根据双耳效应听到的同时来自不同方向的同一方向的同一声音就是立体声，人听到立体声的条件：一是耳朵完好；二是至少有两个扬声器。六、声音的特性六、声音的特性1.音调、响度和音色组成了声音（乐音）的三要素。项目音调响度音色概念声音的高低声音的大小或强弱声音的特色决定因素频率振幅和距离发声体本身，如材料、结构等描述尖细和低沉响亮或微弱改变方法改变发声体的松紧、长短、粗细等改变振幅的大小等改变发声体的材料或结构等描述如尖锐刺耳如震耳欲聋如闻其声知其人专业好文档第 5 页 共 11 页说明频率：是指物体在 1s 内振动的次数，表示物体振动的快慢，单位是赫兹，简称赫，符号是 Hz（声音的音调越高，波形越密）振幅：是指物体振动时偏离中心位置的最大距离注意：注意：人能感受到是声音的频率范围为 202000Hz。高于 2000Hz的声音叫超声波，低于 20Hz声音叫次声波。所以人类听不见超声波和次声波。2.探究实验探究：响度与什么因素有关？（1）过程：如图，将系在细绳上的乒乓球轻触正在发生的音叉，观察乒乓球被弹开的幅度。使音叉发出不同响度的声音，重做上面的实验。加大力度敲音叉时，改变了音叉的振幅，不能改变音叉振动的频率，但振幅，不能改变音叉振动的频率，但振幅大了，响度也大了。（2）结论声音是物体振动产生的。1振幅越大，响度越大。2乒乓球的作用：乒乓球的作用：音叉振动不明显，为了观察到音叉的振动，借助于专业好文档第 6 页 共 11 页乒乓球的跳动来放大音叉的振动。七、声的利用七、声的利用1.回声定位蝙蝠能根据回声到来的方向和时间确定目标的位置和距离。科学家利用回声定位原理发明了声呐，可以探知海洋深度、获得水中鱼群的信息。2.传递信息军事航空上，利用雷达进行探测定位和导航；医疗上，利用 B 超进行身体检测，中医诊断“问其声”；用台风产生的次声波来判断台风的风向及位置；利用地震、机器产生的次声波来判断地震的位置、机器的好坏。3.传递能量超声波传递的能量可用来清洗钟表等精细的机械。外科医生可以利用超声波除去人体内的结石。八、噪声的危害和控制八、噪声的危害和控制1噪声（1）从物理学的绝度讲，噪声是指发声体做无规则的振动时发出的声音。但是从环境保护的觉得看，凡是妨碍人们正常休息、学习和工作的声音，以及对人们要听的声音起干扰作用的声音，都属于噪声。2.噪声的来源（1）交通运输：各种交通工具的喇叭声、汽笛声、刹车声、排气声、专业好文档第 7 页 共 11 页机械运转声等。（2）工业机器：纺织厂、印刷厂、机械车间的噪声。（3）施工机械：筑路、盖楼、打桩等。（4）社会生活：家庭噪声，娱乐场所、商店、集贸市场里的喧哗声。3.噪声的等级危害人们用分贝来划分声音的等级。0 分贝是人们刚刚能听到的最弱声听觉下限；10 分贝相当于微风吹落树叶的沙沙声；3040分贝是比较理想的安静环境；超过 50 分贝就会影响睡眠和休息;70分贝以上会干扰谈话，影响工作效率。长期生活在 90 分贝以上的噪声环境，会严重影响听力和引起神经衰弱、头疼、高血压等疾病。如果突然暴露在高达 150 分贝的噪声环境中，听觉器官会发生剧烈外伤，引起鼓膜破裂出血，双耳完全失去听力。为了保护听力，应控制噪声不超过 90 分贝；为了保证工作和学习，应控制噪声不超过70 分贝；为了保证休息和睡眠，应控制噪声不超过 50 分贝。4.控制噪声的途径（1）在声源处减弱。防止噪音产生。如换用噪声小的设备或加一些消声装置。（2）在传播途径中减弱。阻断噪声的传播。如在马路和住宅间设立屏障或植树造林。（3）在人耳处减弱。防止噪声进入耳朵。如可以戴上防噪声耳塞，或者在耳朵中塞一小团棉花。专业好文档第 8 页 共 11 页Winger Tuivasa-Sheck,who scored two tries in the Kiwis 20-18 semi-final win over England,has been passed fit after a lower-leg injury,while Slater has been named at full-back but is still recovering from a knee injury aggravated against USA.Both sides boast 100%records heading into the encounter but Australia have not conceded a try since Josh Charnleys effort in their first pool match against England on the opening day.Aussie winger Jarryd Hayne is the competitions top try scorer with nine,closely followed by Tuivasa-Sheck with eight.But it is recently named Rugby League International Federation player of the year Sonny Bill Williams who has attracted the most interest in the tournament so far.The Kiwi-with a tournament high 17 offloads-has the chance of becoming the first player to win the World Cup in both rugby league and rugby union after triumphing with the All Blacks in 2011.Id give every award back in a heartbeat just to get across the line this weekend,said Williams.The(lack of)air up there Watch mCayman Islands-based Webb,the head of Fifas anti-racism taskforce,is in London for the Football Associations 150th anniversary celebrations and will attend Citys Premier League match at Chelsea on Sunday.I am going to be at the match tomorrow and I have asked to meet Yaya Toure,he told BBC Sport.For me its about how he felt and I would like to speak to him first to find out what his experience was.Uefa has opened disciplinary proceedings against CSKA for the racist behaviour of their fans during Citys 2-1 win.Michel Platini,president of European footballs governing body,has also ordered an immediate investigation into the referees actions.CSKA said they were surprised and disappointed by Toures complaint.In a statement the Russian side added:We found no racist insults from fans of CSKA.Baumgartner the disappointing news:Mission aborted.The supersonic descent could happen as early as Sunda.The weather plays an important role in this mission.Starting at the ground,conditions have to be very calm-winds less than 2 mph,with no precipitation or humidity and limited cloud cover.The balloon,with capsule attached,will move through the lower level of the atmosphere(the troposphere)where our day-to-day weather lives.It will climb higher than the tip of Mount Everest(5.5 miles/8.85 kilometers),drifting even higher than the cruising altitude of commercial airliners(5.6 miles/9.17 kilometers)and into the stratosphere.As he crosses the boundary layer(called the tropopause),e can expect a lot of turbulence.The balloon will slowly drift to the edge of space at 120,000 feet(Then,I would assume,he will slowly step out onto something resembling an Olympic diving platform.They blew it in 2008 when they got caught cold in the final and they will not make the same mistake against the Kiwis in Manchester.Five years ago they cruised through to the final and so far history has repeated itself here-the last try they conceded was scored by Englands Josh Charnley in the opening game of the tournament.That could be classed as a weakness,a team under-cooked-but I have been impressed by the Kangaroos focus in their games since then.专业好文档第 9 页 共 11 页They have been concentrating on the sort of stuff that wins you tough,even contests-strong defence,especially on their own goal-line,completing sets and a good kick-chase.Theyve been great at all the unglamorous stuff that often goes unnoticed in the stands but not by your team-mates.It is as though their entire tournament has been preparation for the final.In Johnathan Thurston,Cooper Cronk,Cameron Smith and either Billy Slater or Greg Inglis at full-back they have a spine that is unmatched in rugby league.They have played in so many high-pressure games-a priceless asset going into Saturday.The Kiwis are a lot less experienced but winning a dramatic match like their semi-final against England will do wonders for their confidence.They defeated Australia in the Four Nations final in 2010 and the last World Cup,and know they can rise to the big occasion.专业好文档第 10 页 共 11 页Winger Tuivasa-Sheck,who scored two tries in the Kiwis 20-18 semi-final win over England,has been passed fit after a lower-leg injury,while Slater has been named at full-back but is still recovering from a knee injury aggravated against USA.Both sides boast 100%records heading into the encounter but Australia have not conceded a try since Josh Charnleys effort in their first pool match against England on the opening day.Aussie winger Jarryd Hayne is the competitions top try scorer with nine,closely followed by Tuivasa-Sheck with eight.But it is recently named Rugby League International Federation player of the year Sonny Bill Williams who has attracted the most interest in the tournament so far.The Kiwi-with a tournament high 17 offloads-has the chance of becoming the first player to win the World Cup in both rugby league and rugby union after triumphing with the All Blacks in 2011.Id give every award back in a heartbeat just to get across the line this weekend,said Williams.The(lack of)air up there Watch mCayman Islands-based Webb,the head of Fifas anti-racism taskforce,is in London for the Football Associations 150th anniversary celebrations and will attend Citys Premier League match at Chelsea on Sunday.I am going to be at the match tomorrow and I have asked to meet Yaya Toure,he told BBC Sport.For me its about how he felt and I would like to speak to him first to find out what his experience was.Uefa has opened disciplinary proceedings against CSKA for the racist behaviour of their fans during Citys 2-1 win.Michel Platini,president of European footballs governing body,has also ordered an immediate investigation into the referees actions.CSKA said they were surprised and disappointed by Toures complaint.In a statement the Russian side added:We found no racist insults from fans of CSKA.Baumgartner the disappointing news:Mission aborted.The supersonic descent could happen as early as Sunda.The weather plays an important role in this mission.Starting at the ground,conditions have to be very calm-winds less than 2 mph,with no precipitation or humidity and limited cloud cover.The balloon,with capsule attached,will move through the lower level of the atmosphere(the troposphere)where our day-to-day weather lives.It will climb higher than the tip of Mount Everest(5.5 miles/8.85 kilometers),drifting even higher than the cruising altitude of commercial airliners(5.6 miles/9.17 kilometers)and into the stratosphere.As he crosses the boundary layer(called the tropopause),e can expect a lot of turbulence.The balloon will slowly drift to the edge of space at 120,000 feet(Then,I would assume,he will slowly step out onto something resembling an Olympic diving platform.They blew it in 2008 when they got caught cold in the final and they will not make the same mistake against the Kiwis in Manchester.Five years ago they cruised through to the final and so far history has repeated itself here-the last try they conceded was scored by Englands Josh Charnley in the opening game of the tournament.That could be classed as a weakness,a team under-cooked-but I have been impressed by the Kangaroos focus in their games since then.专业好文档第 11 页 共 11 页They have been concentrating on the sort of stuff that wins you tough,even contests-strong defence,especially on their own goal-line,completing sets and a good kick-chase.Theyve been great at all the unglamorous stuff that often goes unnoticed in the stands but not by your team-mates.It is as though their entire tournament has been preparation for the final.In Johnathan Thurston,Cooper Cronk,Cameron Smith and either Billy Slater or Greg Inglis at full-back they have a spine that is unmatched in rugby league.They have played in so many high-pressure games-a priceless asset going into Saturday.The Kiwis are a lot less experienced but winning a dramatic match like their semi-final against England will do wonders for their confidence.They defeated Australia in the Four Nations final in 2010 and the last World Cup,and know they can rise to the big occasion.