- 1、本文档共23页,可阅读全部内容。
- 2、原创力文档(book118)网站文档一经付费(服务费),不意味着购买了该文档的版权,仅供个人/单位学习、研究之用,不得用于商业用途,未经授权,严禁复制、发行、汇编、翻译或者网络传播等,侵权必究。
- 3、本站所有内容均由合作方或网友上传,本站不对文档的完整性、权威性及其观点立场正确性做任何保证或承诺!文档内容仅供研究参考,付费前请自行鉴别。如您付费,意味着您自己接受本站规则且自行承担风险,本站不退款、不进行额外附加服务;查看《如何避免下载的几个坑》。如果您已付费下载过本站文档,您可以点击 这里二次下载。
- 4、如文档侵犯商业秘密、侵犯著作权、侵犯人身权等,请点击“版权申诉”(推荐),也可以打举报电话:400-050-0827(电话支持时间:9:00-18:30)。
Ch20 SOUNDSoundisacompressionwaveinanelasticmedium.Thesecanincludesolids,liquidsandgasoraplasma.
Humanhearingcandetectsoundwaveswithfrequenciesbetween 20Hzand20,000Hz(20kHz).Frequenciesbelow20Hzarecalledinfrasonic. They areinaudible to human hearing.(Wecan’thearthem!)
Frequenciesabove20,000Hzarecalledultrasonic.Theyarealsoinaudibletohumanhearing.(Again,wecan’thearthem,butsomeanimalcan!)
MediaThatTransmitSoundAnyelasticmaterialcantransmitsound.SteelisaverygoodconductorofsounWaterisnotasgood aconductorassteel,butisbetterthanair.Airisapoorconductorofsound
SpeedofSound Soundwaveswillhavedifferentspeedsindifferentmedia.Thespeedalsovarieswithtemperature.Soundtravels15timesfasterinsteethaninair,andittravels 4timesfasterinwaterthaninair.Soundtravelsatabout330m/sinairat 0oCand340m/sinairat20oC.
ReflectionofSoundEcho-Thereflectionofsound.E.G.Singingintheshower.Soundreflectsoffofasmoothsurfaceatthesameangleatwhichitiincident.(i.e.Theangleofreflectionequalsangleofincidence.)
Refraction Refractionisthebendingof thesoundwave.Soundwavesbendwhenpartsofthewavefronttravelatdifferentspeeds.Thisoccurswhenthereare:–UnevenWinds.–UnevenTemperatures.Thespeedofsoundisslightlyfasterinwarmairthanincoolair.
EnergyinSoundWaves Soundgenerallytransmitsonlyasmalamountofenergy.(10,000,000peopletalkingatthesametime=energyneededtolightacommonflashlight).Soundenergydissipatestothermalenergy(heat)whilesoundtravelsthroughair.
Highfrequencysounddissipatestothermalenergymorerapidlythanlowfrequencysound.Hence,lowfrequencysoundhasagreaterrangeinairthanhighfrequencsound.(Foghornstypicallyproducelowfrequencysound,buthavealongrange)
ForcedVibrations Thesettingupofvibrationsinanobjectbyavibratingforce.Examples:Sou
文档评论(0)