A BOOK OF SCIENCE 1.docx

A BOOK OF SCIENCE 1.docx

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ABOOKOFSCIENCE1

THEFIRSTVOLMEOF

ABOOKOFSCIENCE

CONTENTS

1.SOLIDTHINGS….................................................................2

2.LIQUIDTHINGS....……….…….....................................……5

3.GASES.……………………….......................................……8

4.SOLID,LIQUID,ANDGASES.....................................……11

5.MOLECULESANDATOMS...............................................14

6.COMPOUNDSANDMIXTURES......................................17

7.CRYSTALS..........................................................................20

8.CARBON..............................................................................23

9.HOTANDCOLD.................................................................26

10.HOWFRICTIONCAUSESHEAT......................................30

11.HEATANDENERGY..........................................................34

12.BURNING............................................................................38

13.EXPLOSIONS......................................................................41

14.AIR.......................................................................................44

15.VACUUMS...........................................................................47

16.SUCTIONANDSYPHONING............................................50

17.CAPILLARYACTION........................................................53

18.FLOATINGANDSWIMMING...........................................56

19.PRESSUREANDPMPING.................................................59

20.GRAVITY-1..........................................................................62

21.GRAVITY-2..........................................................................65

1.SOLIDTHINGS

Ifyougocamping,youwillneedtosetupatent,andthismeansthattentpegsmustbehammeredintotheground.Usingawoodenmallet,youhammerineachpeguntilthereisenoughofitinthegroundtokeepafirmholdontheguyropefromthetent.Yethowevermuchthetentpeghastobehammeredintotheground,italwayskeepsthesamshape.Thisisbecausethepegismadeissolidwood,andisharderthanthattheground.

Thenwoodforatentpegcomesfromatree,butbeforethetreecanbeusedformakingpegsorplanks,oranythingelse,itmustbefelled.Anaxeisoftenusedforfellingatree.Theheadofanaxeismadeofasolidmetalsuchasironorsteel,whichismuchharderthanwood.Whenthewoodmanswingshisaxeagainstatree,theaxekeepsitsshape,butthesoftertreedoesnot,andpiecesarechippedoff.Whenenoughofthetreetrunkischippedaway,thetreefallsandcanbesenttothesawmillswhereitisslicedupwithsteelsaws.Itcanevenbegroundupintosawdust,whenithasnoneofitsshapeleftatall.

Althoughmostmetalsarefarharderthanmostkindsofwood,theyarenotthehardestsubstancesknown.Thehardestthingofallisadiamond,anditspointededgewilleasilyscratchatoughmetalsuchassteel.Indeed,itispossibletomakeasawthathasdiamondinsteadofmetalteeth,anditwillnotonlycutwillevenslicestraightthroughablockofglass.

If,then,wewanttocutsomethingthatissolid,wemustalwaysdosowithanothersolidthatisharder.Forinstance,itisnogoodtryingtohammerawoodenpegintoabrickwallbecausethebrickistoohardandthewoodwillbreak.Yetasteelnailwillcertainlygoin,sincesteelisfarharderthanbrick.

Solidthings,therefore,keeptheirshapeexceptwhentheyarehitbyothersolidswhichareharder.Butsolidsvaryinotherwaysaswellashardness.Ifwethrowstonesatthem,forexample,theresultisdifferentfordifferentsubstances.Astonethrownatthesteelpillarofabridgewillbounceoffand,exceptperhapsformakingasmalldent,itwillhavenoeffectatallonthesteel.Astonethrownatabrickwallwillalsobounceoff,butthistime,insteadofmakingaslightdent,itwillchipasmallpieceoutofthewall.Brickisnotastoughassteel,andalsoitdoesnotbendor‘give’alittleassteeldoes,butitisfarmore‘brittle’,consequentlythebrickchips.Glass,too,ishard,asbrickandsteelis,butitisverymuchmorebrittlethaneither.Astonethrownataglasswindowwillcrackorevenshattertheglassaltogether.

Therearesomesolidsthat‘give’orbendquiteeasilyandarenotbrittleatall.Thestonethrownatthesteelpillarmightdentitslightly,butifthrownatatinwhichismadeofthinsteel,itwillnotbreakthetinbutitwillbendit,andprobablyquitealteritsshapeor‘deform’it.Ifthestonehitsaleadwaterpipe,theleadwillbendtoo,evenmorethanthetin.Steelandleadarequitedifferentkindsofsolidfromglass—theydonotcrack,buttheydobend,steelwithdifficultyandleadmoreeasily.

Differentsolidsubstances,therefore,havedifferentqualities.Somebendeasilyothersarebrittle,Solidssuchasironandsteelareverytough,whereasothers,suchaspaper,cardboard,andmostkindsofwood,aremuchlesstoughandcanbecutandshapedquiteeasily.Engineersandmanufacturersneedtoknowveryexactlyhowhard,tough,brittle,orbendableanysubstanceiswhentheyaremakingthings,especiallythingssuchasbridgesoraircraftwhichhavetocarrygreatweightsorstandseverestrains.

Thequalityofasoliddoesnotalwaysremainthesame.Alumpofbutterwhichhasbeeninacoldrefrigeratorhasadefiniteshapesandisquitehard;butifitisleftinawarmroomitbecomessofterandmaybegintoloseitsshape.Ifitisleftnearthefire,sothatitbecomesverywarm,itwillloseitsshapealtogetherandbecomeliquid.Mostsolidsgrowsofterwhentheyareheated.Butveryhardsolidssuchasstoneororiondonotbecomesofteruntiltheyareveryhotindeed,sointheeverydayworldarounduswealwaysfindthemhardandstrong（seealsoChapter4）.

2.LIQUIDTHINGS

ThecoldestlandonEarthliesroundtheSouthPole.Itisahugecontinent,biggerthanthewholeEuropeandtheU.S.Aputtogether,andthereisnothingbuticeandsnowandalittlebarerockonsomeofthemountains.Yetscientistsarelivingthere,studyingtheweatherandexaminingtherocksthatlieunderneaththeice,andtheystayformonthsandend.Iftheywantwaterforwashing,orfordrinking,thentheyhavetogathersnoworiceandheatit.Astheyheatit,soitmeltsandturnsintowater.

Thesamekindofthinghappenswithanice-cream.Whenitcomesoutoftherefrigeratoritsitslikealumpatthetopofthecone.Sometimesitisround,sometimesalmostsquare;butineithercaseitissolid.Thenasitbecomeswarmerandasyoueatit,theice-creammelts.Asitmelts,itturnsintoamilkyliquidthatrunseverywhereunlessyouarecareful.

Iceisquitehardandsolid.Duringaverycoldwinter,thewaterinatankoutsideahousewillbefrozen,andtheicewillbeonelarger,solidlump.Ifthereisatapatonesideofthetankanditisturnedon,nothingwillhappen,becauseasolidlumpcannotflowthroughthetap.Butwhentheweatherbecomeswarmer,theicewillmeltandchangetowater.Thewatercantakeanyshape,anddoesnotkeepinasolidblockliketheice,soitwillrunthroughthetapandflowaway.

Waterisaliquid,andallliquidstaketheshapeofwhateverisholdingthem.Ifwaterispouredintoaglasswithstraightsides,itwillfilltheglassandhavethesameshapeastheinsideoftheglass.Butifitispouredintoashallowcuporabasin,itwilltaketheshapeofthebasinorthecup.Thesamethinghappenswithmilk,orwithtea,orwithanyotherliquid.Andifyouspillwaterontheflcor,itrunsallovertheplace,becauseithasnothingtomakeitkeepaspecialshape.

Waternotonlytakestheshapeofwhateveritscontainmaybe—aglass,acup,orabasin—butitalsopressesontheinsideofthatcontainerasifitistryingtoescape.Agoodwayofshowingthisistofillatalltinwithwater,standitbytheedgeofasinkorabath,andpiecethreeholesinit:

oneholenearthetop,oneinthemiddle,andonenearthebottom.Waterpoursoutfromallthreeholes,butitspurtsoutfurtherfromthemiddleholethanfromthetopone,andfromthebottomholeitspurtsoutfurthestofall.

Thereasonwhythewaterspurtsoutfurtherfromthelowerholesisbecauseitispressedoutwithastrongerpush.Thepushorpressurecomesfromthewaterthatliesabove,andsincemorewaterliesabovethemiddleholethanabovethetopone,thewaterwillspurtoutfurther.And,ofcourse,sincethereismorewaterlyingabovethebottomholethanabovetheothertwo,thepressuretherewillbethegreatest,andthewaterwillspurtoutfurtherstill.

Thepressureonthewateriscausedbytheweightofthewater.Peopledonotalwaysthinkofwaterasweighinganything,butifyouliftanemptybucketandthenliftafullone,youimmediatelyknowthatwaterisquiteheavy.Inthetinwithholesinit,thepressureonthebottomholeiscausedbytheweightofallthewater,butthepressureonthemiddleholeiscausedbytheweightofonlyhalfthewaterpressingonit;thetopholehasverylittleweightatallaboveit,andsothepressurethereisleastofall.

Ifyoutakeatinofsoupandpunchoneholeinthetop,youwillfindthatthesoupdoesnotrunout.Evenifyoutipthetinupsidedown,andtheweightofallthesouppressesonthehole,nosoupwillcomeout.Why?

Thereasonisthatnosoupcanleavethetinunlesssomethingelsecangetintotakeitsplace.Butnoaircangetintothetinifthereisonlyoneholebecausethesoupisblockingthehole.Ifyoupunchanotherhole,thenthesoupwillpourouteasilyfromonehole,andairwillenterbytheothertotakeitsplace.Ifyouputafingeroverthesecondhole,thentheflowwillstop.Thisiswhyacontainermusthavetwoholesforittopourproperly,andthatiswhythereisalwaysaholeinthelidofateapot.

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