Natural Sciences Grade 8 - CNX

1 Natural Sciences Grade 8By:Siyavula UploadersNatural Sciences Grade 8By:Siyavula UploadersOnline:< >C O N N E X I O N SRice University, Houston, ( ).Collectionstructurerevised:Septemb er12,2009 PDFgenerated:Octob er28,2012 Forcopyrightandattributioninformationfor themo dulescontainedinthiscollection, egin.. electricity.. ower.. cabularyforelectricity.. erature.. ectionandrefractionoflight.. cksofmatter.. ounds.. oundsandmixtures.. :habitat.. opulation.. erentecosystems.. ecialfo o drelationships..135 Attributions.. 140ivAvailableforfreeatConnexions< > chapter 1 Term :ELECTRICITY, dule1:Energytob : (J). Therearetwomaintyp esofenergy: TheenergyofactionormotionisknownasKINETI C energy Theenergyofp ositionisknownasPOTENTIAL energy Energyalsoo ccursinvariousforms, :Chemicalenergy,whichisobtainedfromchemi calsubstanceslikep etroleum,oil,gas,batteriesandfo o d-stu s;Electricalenergy,whichisderivedfromele ctricity;Soundenergy,fromloudsp eakersRadiantenergy, , erenttyp [ , , ]AssignmentInthefollowinglist, < >.

2 AvailableforfreeatConnexions< > erband(sho oting) o owerstationAssessmentofformsofEnergyWere youabletoindicatetheformsofenergycorrect ly?[ ] :ConstructingScienceKnowledge:Thelearner willknowandb eabletointerpretandapplyscienti c, : recallsmeaningfulinformation; categorisesinformation; (b eingshot) o d owerstation KINETICTOELECTRICAL Explainthistograde8withthehelpofasimplee xample. Itisgenerallyknownthatthecommonlightbulb providesuswithlight,butalsob ecomessohotthatitcanhardlyb out5J,whiletheheatequalsab out95J. Theconversionthereforeisasfollows: ELECTRICENERGYTOLIGHTENERGYANDHEATENERGY Alightbulbthereforeisaltogetheruneconomi cal! Ifyouconsiderthis,youwillrealisethatthef o o dprovidestheSOURCEOFENERGY ofhumanb eings,butelectricityandfuelsprovideallot herasp < > :ELECTRICITY, Atpresent,mostofourenergyisderivedfromfo ssilsources(coal,oil,naturalgaswithsecon darypro etroleum) nditdi culttoimagineaworldwithoutelectricity,th isenergysourceisnotavailableinmanypartso fSouthAfricaandtheAfricancontinent.

3 InSouthAfrica,energyisprovidedindi erentforms,themostimp ortantb eingelectricityandliquidfuels(re nedfromcrudeoilandcoal),coalandbiomass( rewo o d).Themainsourcesofenergyforgeneratingel ectricityinSouthAfricaare:burningofcoal; hydro electricity;nuclearp [ , ]Atpresent,coalisthemostgenerallyusedsou rceofenergy,topro duceelectricity, owerstationspro duceroughly90%ofthecountry' :VisittheEskomwebsiteto ndmoreinformationab outthistyp eofp erationofatypicalp estheacronymESKOM standfor?Towhomistheelectricitysupplied? Assignment2:Completethefollowingtabletor epresentthep ower-generatingpro cessbyplacingthedi erentstepsofthispro < >.AvailableforfreeatConnexions< > :Answerthefollowingquestions,makinguseof theinformationyouhavegainedconcerningthe pro enstothesteamthatdrivestheturbines? eratethissystemforaday? clean withregardtonature?Assessmentofthestepst hatarefollowedinthepro cessofgeneratingelectricity:Wereyouablet oplacethestepsinthecorrectorderandanswer thequestionscorrectly?

4 [ ; ] :ConstructingScienceKnowledge:Thelearner willknowandb eabletointerpretandapplyscienti c, : categorisesinformation; interpretsinformation; InSouthAfricathemainsourcesofenergyusedt ogenerateelectricityare: Burningofcoal Hydro electricity Nuclearp owerCOAL-BURNINGANDPOWERSTATIONSA ssignment1 Atpresent,thisisthemostgenerallyusedsour ceofenergy,andthereforeofelectricity, owerstationspro duceroughly90%ofthecountry' < >5 ESKOM ELECTRICITYSUPPLYCOMMISSION Thisorganisationprovides95% ,acoal- ringp owerstationop eratesasfollows:Assignment2 Coalisminedandtransp ortedCoalisgroundCoalisburnedWaterinpip esisheatedtoprovidesteamSteamdrivesthetu rbinesTurbinesturntherotorofthegenerator Therotorisanelectromagnetthatgeneratesel ectricityElectricityiscarriedawaybymeans ofcopp :Thesteamthatturnstheturbineshastoescap esomewhere-Ithastob econdensedthroughco oling,andthisrequireswater!

5 Eachp owerstationrequiresapproximately150milli onlitresofwaterp oration!Typicalco olingtowerscanb eseenalongtheN2justoutsideCap cesscomprisesharmfulgaseslikesulphurdiox ide,carb ondioxide,andnitrogendioxide eseenasa"clean"metho dandisharmfultonatureb ecauseoftheresultantairp ollution,acidrainandparticlesofashpump :Electricity, [ , , ]Weliveinaverydrycountry,butwedohavetwol argep ermanently owingriversandESKOM haserectedtwolargehydro electricp < >.AvailableforfreeatConnexions< > :Findoutwherethesetwolargedams(andanyoth erlargedams),aresituatedanddrawamapofSou thAfricatoindicatetheirp cationofDamsWereyouabletoidentifythedams correctly?Hydro electricitycanbasicallyb eexplainedinbriefbymeansofthefollowingp oints: Thedownwardmovementofwater,duetogravitat ionalpull,energisesthemoleculesofwater. Thefallingwaterturnsaturbineandconvertst heenergyofthemoleculestoelectricenergy.

6 Thetransferofenergytosomeorotherturningm echanismhasb :Readand ndoutmore:VisittheInternetanduseasearche ngine,usingwordslike aqueduct and waterwheel . electricityandcoalburningassourcesofener gy[ , ]Assignment1:Completethefollowingtablede alingwithcoal-burningp owerstationsasopp osedtohydro electricp owerstationswithregardtothefollowinghead ings:Decidewhetheryouaredealingwithanadv antageordisadvantageineachinstanceandmar kthecorresp < >7 Asp ectCoalp owerHydro electricityAdvantageDisadvantageAdvantag eDisadvantagePollutionCostJob-creationRe servesSp eedofpro :Scienti cinvestigations:Thelearnerwillb eabletoactcon dentlyoncuriosityab outnaturalphenomena,andtoinvestigaterela tionshipsandsolveproblemsinscienti c, : plansinvestigations; conductsinvestigationsandcollectsdata; evaluatesdataandcommunicates :ConstructingScienceKnowledge:Thelearner willknowandb eabletointerpretandapplyscienti c, : categorisesinformation; interpretsinformation.

7 :Electricity, [ , , ]Assignment1:4 Thiscontentisavailableonlineat< >.AvailableforfreeatConnexions< > jecton Nuclearp owerinSouthAfrica Divideintogroupsforcollectinginformation onnuclearp 'snuclearp owerstation?Howmuchelectricityisprovided bythisp owerstation?Towhomisthiselectricityprovi ded?Whichdangerousmetalisusedinthep ower-generatingpro cess?Whyisco olinganimp ortantcomp onentofthisp ower-generatingpro cess?Isittruethatyouneedtoburn25railwayt ruckloadsofcoaltoobtainthesameamountofen ergythatisprovidedbyapieceofuraniumthesi zeofonegolfball? oster?[ ; ]Assignment2:Haveaclassdiscussiononwheth ernuclearp [ ] :Scienti cinvestigations:Thelearnerwillb eabletoactcon dentlyoncuriosityab outnaturalphenomena,andtoinvestigaterela tionshipsandsolveproblemsinscienti c, : plansinvestigations; conductsinvestigationsandcollectsdata; evaluatesdataandcommunicates :Science,So cietyandtheEnvironmentThelearnerwillb eabletodemonstrateanunderstandingofthein terrelationshipsb etweenscienceandtechnology,so : Doapro jecton Nuclearp owerinSouthAfrica Thelearnershavetob edividedintogroupsforcollectinginformati ononnuclearp : WhereisSouthAfrica'snuclearp owerstation?

8 ATDUINEFONTEINNEARMELKBOS Howmuchelectricityisprovidedbythisp owerstation?6%+TOOTHERCOUNTRIES Whichdangerousmetalisusedforthep ower-generatingpro cess?ENRICHEDURANIUM Whyisco olinganimp ortantcomp onentofthisp ower-generatingpro cess?BECAUSEOFTHEIM-MENSEHEATTHATISGENER ATEDA vailableforfreeatConnexions< >9 Isittruethatyoucanburn25railwaytruckload sofcoaltoobtainaquantityofenergyequaltot hatwhichisprovidedbyanamountofuraniumtha tisequaltothesizeofonegolfball? YES Visit: Manyp eopleb ecomequiteconcernedwhentheythinkofnuclea rp owerb ecauseofthehorroroftheSecondWorldWarandH iroshima,etc. TheSouthAfricannuclearreactorislo catednorthofCap eTownatKo eb ,5%ofthecountry'selectricity. TheKo eb ergp owerstationistheonlynuclearp ,eachofwhichdevelops960 MWofp ercentofthep owerofthatisdevelop edinSouthAfrica. Ko eb ergsupplieselectricitytothewholeoftheWes ternCap eandexp ortssurpluscapacitytootherpartsofSouthAf ricaandtoNamibia,ourneighb our,duringthesummer.

9 Althoughistheonlynuclearp owerstationinAfrica,thereare438nuclearp ,namely118,areinNorthernAmericaandsupply approximatelytwentyp ercentofAmerica' ,76p ercentofthetotalp owerdevelopmentcapacitycomefromnuclearp endonnuclearfacilitiestoprovideatleastaq uarteroftheirtotalelectricityrequirement . Inspiteofthep erceptionthattheuseofnuclearp owerisb eingreduced,therearede niteplanstoextendtheuseofnuclearp owerinChina,India, owerinstallationswerelinkedtoelectricity networksin2000,andbuildingwascommencedon threenewnuclearreactors erofnuclearreactorsthatareb : Fuel Uranium(U). Amo derator whichslowsdownpro cesses almostlikeasystemofbrakes. Controlro ds tostopareaction. Co olingagent whichisabletoco oldownenormousheat. Protectivecoveringtoprotectp eoplefromradioactiveradiation cessisasfollows: Enricheduraniumissplit( ssion)undercontrolledconditions. Splittingofoneatomofuraniumprovides10mil liontimestheamountofenergythatisobtained fromburningoneatomofcarb on!

10 Thenuclearreactionreleasesanenormousamou ntofheat. Theheatconvertstoseam. Thesteamdrivesaturbine,which,inturn,driv esagenerator. Thesteamiscondensedandpump edbacktoco cess: Theenricheduraniumhastheformofsmallparti clescoatedwithlayersofcarb Thefuelcomesintheformofballs, , < > Theheatthatisgeneratedduringthenuclearre actionisb orneawaybymeansofheliumgas,whichentersth ereactoratab out500 C,movesacrossthereactorfuelandleavesther eactoratab out900 , :ELECTRICITY, Nowthatwehavecompletedthepreviouslearnin gunit,itisclearthatweshallhavetoinvestig atealternativesourcesforourcountry'sener gyandelectricitysupply. Thesourcesthatwearereferringtoareknownas RENEWABLEENERGYSOURCES,andafairamountofi nformationonthesesourcesisavailable. Renewableenergysourcesreferto:SOLARPOWER :Solarpanelsthatcanrunheatingsystemsinst alledonthero ofsofhouses,solarcellsincalculatorsandin somecars, [ , , ]Assignment1:Workinpairsanddesignabro cuson: yourmotivationforpromotingthistyp eofsource, ; adiagramtobrie yandsimplyillustratetheop erationofthismetho db earinginmindthatyouaretryingtoexplainthi stoordinaryp eople; howthistyp eofenergysourceb ene tsorharmstheenvironment; problemsonewouldexp eriencewiththeuseofthissource consider nancialasp ects; yourp ersonalopinionandmotivationforconsumerst oconsiderit!