听力1_英语学习_外语学习_教育专区

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1、Unit4OutsideviewToflylikeabird.It'sadesirethatcapturesthehumanimagination.TheGreekstoldstoriesofDaedalus,aninventorwhocreatedwingsmadeofwaxandfeathersandflew.ThefirstpersonwhoseriouslytriedtoflylikeabirdwasanItalianartistandinventor^LeonardodaVinci.DaV

2、incidesignedcomplexandwondrousflyingmachines,buthisdesignsnevergotofftheground.Earlyinventors,likedax/inci*triedtoflybyflapping,justlikebirds.Hereiswhathappenswhenabirdflaps:Whenabirdflaps,thrustandliftandcontrolarecreatedatthesametime.Liftistheforceth

3、atkeepsthebirdelevated・Liftisgeneratedbytheairunderthebird'swings.Thrustistheforcethatkeepsthebirdmovingforward・Thrustisgeneratedbypowerfulmusclesinthebird'schestandwings.Thebirdmaintainscontrolbyconstantlyadjustingitsflapping.Muchofabird'scontrolisgen

4、eratedbyitstail.Asuccessfulflyingmachineneededtoprovidethesameforcesthatabirdused,Asuccessfulflyingmachineneededtoprovidelifttoovercomegravity,controltoletthedriverchangedirection.Andthrusttomakeitmoveforward.Anditneededtobelightenoughtostayintheair.On

5、ceinventorsunderstoodthesethreechallengesseparately,andstoppedtryingtoflap.theymadeprogress.OneinventorwastheBrazilianpilotandaviatorAlbertoSantos-Dumont.Santos-Dumontexperimentedwithballoons・Heflewhislighter-than-airflyingmachinesinFrance.In1901,Santo

6、s-DumontwasthefirsttoflyfromSantCloudtotheEiffelTowerandbackinagiventime.Meanwhileotherinventorswereworkingonheavier-than-airflyingmachines.Withtheseaircraft,liftwasabigproblem.Germanflyer#OttoLilienthal,tackledtheproblemoflift.Hebuiltmanylargegliders,

7、constantlyrefiningtheirdesign・Lilienthalmadethousandsofflightsfromthetopofahill.Somethatlastedaslongasfivehours・Butheeventuallydiedinatragiccrash.Lilienthalsuccessfullymasteredthechallengeoflift,buthedidnotmasterthechallengeofcontrol.TheWrightBrothersw

8、ereinspiredbyLilienthaKsinventions.TheWrightBrothersstartedtodevelopandtesttheirownflyingmachines.IntheirOhioworkshop,theybuiltawindtunnelandstudyaerodynamics.Throughtrialanderror#theydiscoveredhowtheshapesofdifferentwingsaffectedlift.T