物理人教版八年级上册热传递.pptx

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1、Thermalphysics1.Thekineticmodelofmatter2.Thermalpropertiesofmatter3.HeattransferReviewofheattransfer(1)Whatisheattransfer?Heatenergywillalwaystrytomovefromahotterplacetoacolderplace–inotherwords,fromhighertemperaturetolowertemperature.Thisiscalledheattransfer.Heatener

2、gycanbetransferredinthreeways:ConductionConvectionRadiationConduction–heattransferredthroughamatterbyparticlescollidingintooneanother.videoHowdoesconductionhappen?Andwhydometalsconductheatveryquickly?HowcanheatWhyaremetalsgoodthermalconductorenergymovethroughmatter?An

3、dwhyaremetalsgoodthermalconductor?VIDEO?Whyaremetalsgoodthermalconductor?Whenyoufingertouchametalspoon-itfellscold.youpickupaplasticspoon–itfeelswarm.Doyouknowwhy?Whatistheconclusionofthisexperiment?Somematerialsallowheattoquicklypassthem(suchasmetals).TheyarecalledSo

4、mematerialsdonotallowheattoquicklypassthroughoutthem(suchaswoodorplastic).Theyarecalledthermalconductorthermalinsulator.Whatdoestheexperimentshowus?Convectioncannothappeninsolid.Waterisathermalinsulator,whycanweboilwatereasily?Convection–heattransferredbythecirculatio

5、nofafluid(liquidandgas),suchasaheatingsystemathome;WatermovementHotwaterrisesCoolerwatersinksConvectioncurrentCoolsatthesurfaceWhat’shappeninghere?HowdoesheatenergygetfromtheSuntotheEarth?TherearenoparticlesbetweentheSunandtheEarthsoitCANNOTtravelbyconductionorbyconve

6、ction.?RADIATIONRadiation:thetransferofthermalenergybyelectromagneticwaves.(visiblelight,infraredradiation)Radiationdoesnotrequiremattertotransferthermalenergy.Allthesun’senergythatreachesEarthtravelsthroughmillionsofkilometersofemptyspace(avacuum).Thehotteranobjectis

7、,themoreinfraredradiationitemits.Whatkindsofobjectwillabsorboremitmuchmoreinfraredradiation?Thedull(matt)blacksurfacesaregoodemitterandabsorber.EmissionexperimentFourcontainerswerefilledwithwarmwater(withsametemperature).Whichcontainerwouldhavethewarmestwateraftertenm

8、inutes?ShinymetalDullmetalDullblackShinyblackThe__________containerwouldbethewarmestaftertenminutesbecauseitsshinysurfaceref