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ID:5959603
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页数:3页
时间:2017-12-29
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1、WavesHowdoeslightgetfromthesuntotheearth?Howdoesmusicgetfromthestagetotheaudience?Theymovethesameway-----inwaves!Lightandsoundarefomp3sofenergy.Allwavescarryenergy,buttheymaycarryitdifferently.Lightandsoundtravelthroughdifferentkindsofmatter.Forexample,lightwavescannotmovethroughwalls,butsoundwa
2、vescan.Thatiswhyyoucanhearpeopletalkinginanotherroomeventhoughyoucannotseethem.Theenergyofsomewavesisdestructive.Anearthquakeproducesseismicwaves.Catchawave.Askafriendtostandafewfeetawayfromyou.Stretchaspringbetweenyou.Shakethespringtotransferenergytoit.Whathappens?Thespringbouncesupanddowninwav
3、es.Whenthewavesreachyourfriend,theybouncebacktoyou!Lightwavestravel300,000kilometers(186,000miles)persecond!Theycanalsotravelthroughavacuum.Thatiswhylightfromthesunanddistantstarscantravelthroughspacetotheearth!SoilsTherearemanydifferentkindsofsoils.Differentsoilshavedifferenttypesofrockandminer
4、alsinthem.Somesoilshavemorewaterinthemthanothers.Somesoilsmighthavemoreplantandanimalmaterialinthem,too.Differentkindsofsoilsarefoundindifferentpartsoftheworld.ThereareseveralkindsofsoilsfoundintheUnitedStates.Insomeareas,thesoilhasalotofclay.Othersoilsareverysandy.Loamisakindofsoilthathasagoodm
5、ixtureofclayandsand.Insomeplaces,soillayersareverythick.Lotsofplantsgrowinplaceswithathicksoillayer.Indryandwindyplacessoillayersaremuchthinner.Layersofsoilonmountainsarethinbecausegravitypullsthesoildownhill.Thetypeofsoilinaparticularplaceaffectswhatkindsofplantscangrowthere.CrisisLifeisacontes
6、t!Whowillwin?Abluebirdandsparrowbothcompeteforspacetobuildtheirnests.Afast-growingmapletreeandslower-growingdogwoodcompeteforthesunlighttheybothneed.Oilcompeteswithcoalandnuclearpowerasanenergysourceforelectricpowerplants!Thereisaproblem.Thereisalimitedamountofspaceforbirds,sunlightfortrees,ande
7、nergyforpeople!Ifwedonotcutbackonourusesofsomeofourresources,somedaytheywillbegone!Howcanweuseenergytodayandknowwewillhaveenoughtogoaroundinthefuture?Wecanchoosealternate,orreplacement,energyresources.Ittakestheearthmillions
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