SCIENCE GRADE 4 UNIT C PHYSICAL SCIENCE by FREDDY QUITIAN

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DirectedInquiry

Whot is one woy you cqn determine density?

GuidedInquiry

Whot boot designwill corry the most corgo?

AclivityFlip Chort Do wotermoleculeshoveony spoce beiweenthem? How do qtomsdiffer? Quick Aciiviiy Tronsporencies

DirectedInquiry GuidedInquiry

Whot con hoppenduringo chemicol cnonger How doestemperotureoffecthow long o reoctiontokes?

How con moller chonoeform? Whot ore somechemicolreoctions? How ore chemicolpropertieshelpful? H_owis technologyinuolvedin euerydoy lite?

DirectedInquiry

How con you leornobout the motionof o pendulum?

GuidedInquiry

How con you describemotion?

ActivityFlipChort How does inertiooffecl motion? Whot forcesoffecio poddleboll? QuickActivity Tronsporencies

How con energychongeits form?

GuidedInquiry

How does light move?

ActivityFlipChort How do wovesmove? Whot hoppenswhen you mix cólors? Quick Activir¡ Tronsporencies

How is moller meosured? Whot doeson otom look like? How does moiterchonge? Whot ore mixtures?

ActivityFlipChorf Whot con speedup o chemicolreoction? How con you obseweevidenceof o chemicolchonge? Quick Activiiy Tronsporencies

DirectedInquiry

Horvcon y_oumokethingsmove? Whot ore torces? How ore forcesrelotedtrcmotion? How do simplemochinesmokework eosier?

How is energyreloiedto motion? How ore soundsproduced? How con l¡qhtbe bent? Whot is the-rmol energy?

Directed Inquiry

Whot con electricityflow through?

\ruroeo rnqurry

How ore seriesond porollelcircuits different?

ActivityFlipChort How con you useinsulolorsond conductorslo mokeo gome? How con you mop o mqgnefsmqgnehc field? Quick Activit/ Tronsporencies

Whot is stoticelechicity? Whot is o simplecircuit? Whot doeso porollelcircuitlooklike?

FullInquiry

Con you chongeúe polesof on electromognet?

STEMProject

Testo Model Airplone

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element

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OIOÍ| pose348 prOlOn poge348 neulron

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electron poge349

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Explore Whot is onewoy youcon determine density? Moteriqls

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I woodenblock, f stickof cloy, I stickof cloy ¡E¡t@t! melricruler

bolonceond grom cuoes

Whor lo Do Meqsure thelength,width, ond heightof o woodenblock in centimeters. Findthe block's volumein cubiccentimeters. : lengfhx widfh X heighf vol¿¡rne

Useo bolonceto meosurethe mossof the block.Putthe blockon one side.Add grom cubesto the othersideuniilthe 2 sidesbolonce. Findthe totolmossof the grom cubes.Eoch grom cubehoso mossof 1 grom.

colculotoror computer (optionol)

trnthisoclivity you find the densi| of eoch object,using cubiccentimeters ono gromsos the unitsof meosuremenf.

Colculote theblock'sdensity. Thedensityis I number of gromspercubiccentimeter. densifg:Íloss+voldne

Repeot stepsI to 3 withf of o sfickof clo¡ -i of o stickof cloy,ondo gromcube.

Exploin Your Results Gommunicqte Describeone woy to f¡ndthe densityof on object. Whot mustyou meqsure? Tok€ lt to lh€ Net PeorFnslcc8$n€t.cof¡

t@Predict oboutwhotwill Whenyou predicl, you moyosko quesfion hoppennextin o storyond thenthinkof on onswer.Afteryou mokeyour prediction,continuereoding.As you reod,consider new if ony new informotionsupportsyour prediction.Perhops, informotionwill leodyou to mokeo differentprediction.

FictionSfory Science

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Foryeors,Rodneyworkedon building his spoceship. The hordestiob wos finding the right moteriol to use for the toilfins. They hod to be mode of the densestmetol ovoiloble. Unfortunotely,Rodneyhod only tlvo moteriolsleft in his shop.He hod somesquore,thick sheetsof titonium ond chromium. Rodney knew whot he hod to do to moke the rioht choice. ¡¡q{!{i?1X1r*x¡*lrtt}t

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Apply ltl Moke o grophicorgonizerlikethe one shown.Moke o

predicfion obouthow Rodneywill meqsure thedensityof the moteriols. Communicqte your predictionto o clossmote.

Question

How will Rodney meosurethe densify?

Prediction

quYouAreThere! You ore working inside o huge reseorch instrument in o loborotory thot is three stories toll. When your work is done, giont mognets ond other equipment will stort to hum. Tiny porticles, too smoll to see even with o microscope, will zoom through the instrument ot super speed.Theseporticleswill smosh together, forming new types of motter. Scientistsdo experiments like these os they study motter. Scientistshove been studying motter for centuries. Whot hove they leorned?

Thegold in thesenuggets is the pureelement.

Lesson I

What aÍeproperties of matter? ffi AIIthingsaroundusare madewith justa few kindsof matter. Eachkind of matterhas its ownsetof properties.

Elements There ore more thon 100 bosic kinds of motter, colled elements. Elements ore the bosic building blocks of motte¡. Elements combine to moke up oll other kinds of motter. Elements connot be broken into simpler substonceswith ordinory physicol or chemicol processes. Only o few elements, such os gold, ore found in noture in pure form. Most elements ore combined to form the things oround us. For exomple, rust is o combinotion of iron ond oxygen. Living ond nonliving things ore mode of iust o few elements combined in mony woys.

Properties of Elements Eoch element hos its own chemicol ond physicol properties. You con use these properties to identify eoch element. Chemicol properties describe how o mqteriol chonges into other moteriols. Physicol properties con be meosured without chonging the moteriol. Physicol properties include on object's moss, volume, color, odor, ond phose of room temperoture. Physicol properties con be observed, described, ond meosured with tools such os rulers, microscopes,thermometers, scoles, ond bolonces. More than I of the elements ore colled metols. Metols hove the physicol properties ofbeing shiny, bendoble, ond oble to conduct heot energy ond electricity well. l.

.yÓCnecfpoint: Arethingsorounous Howmonyelemenls orethere? usuollymode of pure elementsor combinolionsof elements?

Why do you th¡nkponsore mqdeof metol? fdke l| lo the Not p@rlorsuc.e3snel.com

: keyword: element : codei g5p3¿3

343

Weight ond Mqss Weight is o meosureof the pull of grovity on on object.Springscolesmeosureon oblect'sweight.A spring scolehos o spring thot stretchesor is squeezed togetherwhen you weigh on obiect.The omount thot the spring'slength chongestellsthe obiect'sweight. If on objectis too lorge to hong from o scole,you con odd up the weights.ofoll the obiect'sports. The totol weight of the ports olwoys equolsthe weight of the

By boloncinglhe ioy cor wiih knownmosses, you con meosurethecor's mossio be 8 groms.

whole obiect. Weight chonges when the pull of grovity chonges. Grovity is not the some everywhere on Eorth. For exomple, the pull of grovity decÂĄeosesslightly os on obiect is Iifted to the top of o mountoin. Therefore, the obiect's weight becomes o little less. Moss is the omount of motter in on object. The omount of moss offects the weight of on obiect, but moss is not the some os weight. Moving on obiect to the top of o mountoin does not chonge the omount of motter in on object. Its moss stoys the some. Moss is meosured by using o bolonce, often using units of groms, milligroms, or kilogroms. To find moss, on obiect is ploced on one side of the bolonce. Known mosses ore ploced on the other side. When the two sides bolonce eoch other, the totol moss of oll the known mossesequols the obiect'smoss.

Volume Volume is the omount of spoce thot on obiect tokes up. Cubic units ore used for volume. You con find the volume of o regulor box by meosuring ond multiplying its length, width, ond height. You con write o formulo using V for volume, L for length, W for width, ond H for height. The forrnulo for finding the volume of o box is V : L x W X H. You con use o groduoted cylinder to find the volume of o liquid. You con olso use o groduoted cylinder to meosure the volume of o solid obiect thot Ăąts in the cylinder ond sinks in woter. First, put o meosured omount of woter in the cylinder. Then put the obiect into the woter. Reod the new volume. The difference between the tÂĄ,vovolumes is the volume of the obiect.

344

Withoutfie toy cor, thegroduotedcylinder meosures 50 milliliters of woler.Wth thecor, thewoler levelmeosures 55 milliliters.Whot is thevolumeof lhe cor? Thevolumeof solids ore lobeledwith cubic centimelers. Onecubic (cm3l centimefrer is the someosonemillilircr.

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f% Thisgold bor hos o mossof obout1025g or I .025kg.

Properties of Objecrsond Mqteriqls How mony different woys could you describe the physicol properties of the gold bor obove? There is o difference between on obiectt properties ond o moteriol's properties. You could soy thot the bor's properties include o rectongulor shope with o certoin size ond moss. These properties ore only true for this bor or other bors iust like it. If you cut or bend the bor, some properties will chonge. A moteriol's properties ore the some no motter how you bend, cut, or crush it. Gold's density is the some no motter whot shope it hos. AII pieces of gold ore not ottrocted to mognets. Therefore, these ore gold's properties, not just the bor's properties. Other moteriol properties include color, hordness, ond texture. 1. JCnecfpoint. Is volumeo propertyof on object,or the motler thot mokesit uo? .)

Useo colculotor or spreodsheet to find the volumeof the gold bor picturedobove. Roundyour onswer fo the neorest0.,] cm3.

Density ond Buoyoncy Density is o meosure of the omount of motter in o given volume. To find on obiect's density, divide the obiect's moss by its volume (D : +). For exomple, you could find the density of the cor on the previous poge by dividing its moss, 8 groms, by its volume, 5 cubic centimeters. The density is 1.6 groms per cubic centimeter. Density is o physicol property of o substonce. Density is the some for o substonce no motter how much of the substonce is meosured. For exomple, iron will olwoys hove o density of about 7.9 groms per cubic centimeter, no motter how lorge o piece of iron is meosured. Becouse the density of o moteriol is olwoys the some, it con be used to help identify o moteriol Equol volumes of ony two different substonces usuolly hove different mosses.This meons thot the two substonceshove different densities. Look ot the pictures below. The boll of cloy hos the greoter moss ond the greoter density.

Thisbosebollhoso mossof I I0 g ondo volumeof 195cm3. Its densityis obout

Thisboll of cloyhos o mossof 445 g ond o volumeof 195cm3. Its densityis obout

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Flooting or Sinking An object is buoyont if it floots. Buoyoncy is on importont propefty in boots or bolloons. You olso wont o life jocket to floot ond on onchor to sink. You would use different moteriols for eoch. Whether o certoin moteriol floots in a liquid depends on the densities of both the moteriol ond the liquid. If the obiect's density is lessthon the liquid's density, it will floot. If the object's density is greoter thon the liquid's density,it will sink. The chort on the previous poge shows thot fresh woter hos o density of obout 1 grom per milliliter. Notice thot in the chort, moteriols thot you expect to sink in woter, such os cement ond iron, ore more dense thon woter. Moteriols thot floot in woter, such os pinewood ond cork, hove o density lessthon 1 grom per cubic centimeter. Oceon woter hos dissolvedsolts ond other moteriols. Becouseof this, oceon woter is more dense thon fresh woter. Its density depends on how much moteriol is dissolved in it.

f' LessonCheckpoint howcouldyoutellwhยกchoneis more l. If you hodtwo equollysizedobjects, dense? tobleon lheprevious thotis listedin thedensity 2. Suppose you hodo moteriol Howdo poge.It flootsin wolerbutsinksin oliveoil.Whotisthemoteriol? you know? Descriptive In yoursciencejournol writeo 3. descriptionof on object.Includesomepropertiessuchos color,odor, ond Do you know how Is it o gos, liquid,or solidol roomtemperoture? hordness. well it conductsheot or electricity?Would you expectit to floot?

Lesson2

Howdo atoms t.

comDlneI Atoms are particlesof elements.Atoms combine to form compounds.

All heliumotoms hoveexoctly 2 prolrons ond usuollyhove 2 neufrons ond 2 elecFons.

Atoms An otom is the smollest porticle of on element thot still hos the propertiesof the element. Atoms of one element ore different from otoms of other elements. Atoms ore too smoll to be seen even with o microscope. The properties of otoms determine the properties of on element ond how the element con combine with other elements. The otom's center, or nucleus, usuolly hos both neutrons ond protons. A neutron hos no elect¡icol chorge. A proton hos o positive chorge. An otom is identified by the number of protons it has. For exomple, oll corbon otoms hove six protons. No other kind of otom hos six Drotons.

Theelements in lhiscolumncon eosilyloseone electron.

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Chromiumis used in chromeploting.

Be 6

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Elements thot ore metolscon conductelectricity well. 3

t2 29

Cr Mn Fe Co N¡ Cu Zn Coboll

Nb Mo

Pd Ag

LYir.

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Fr 57

1¡r Ce 89

Lesson2

Howdo atoms lo^l

comDlnef All heliumotoms hoveexoctly 2 protonsond usuollyhove 2 neulronsond 2 electr.ons.

Theelements in thiscolumncon eosilyloseone electron,

Atomsareparticlesof elements. Atomscombineto form compounds.

Atoms An qtom is the smollest porticle of on element thot still hos the propertiesof the element. Atoms of one element ore different from otoms of other elements. Atoms ore too smoll to be seen even with o microscope. The properties of otoms determine the properties of on element ond how the element con combine with other elements. The otom's center, or nucleus, usuolly hos both neutrons ond protons. A neutron hos no electricol chorge. A proton hos o positive chorge. An otom is identified by the number of protons it hos. For exomple, oll corbon otoms hove six protons. No other kind of otom hos six Drotons. Chromiumis used in chromeploting.

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Rb 55

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Cr Mn

Elements thot ore metolscon conductelectricity well. 3456

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Co Ni Cu

Electrons move oround the protons ond neutrons. An electron hos o negotive chorge. Electrons moy join or leove otoms, or be shored between otoms.

The Periodic Tqble Elements ore orgonized in o toble colled the periodic toble of elements. The elements ore orronged in eoch row occording to the number of protons. Lorger otoms ore on the right side of eoch row. The columns of the toble ore orronged so thot the elements in eoch column hove similor chemicol properties. Therefore, you con predict the properties of on element if you know its column. For exomple, in the lost column on the right you will find elements known os noble goses.They do not often combine with other elements. Every element hos o symbol of one, two, or three letters. Only the first letter of the symbol is copitolized. Whot elements hove the symbols C, H, ond Co? Nonmehlsore in thecolumnsto the right They do not conduct electricitywell. r5 l贸

Thelightsin thissign controinneon.

Phoseqt room 眉emperqfure

Key: Symbol Elemenfnome Thenumberin eoch box is the numberof protonsin theoioms of thof element

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.yfCnectpoint. Describe theperiodictobleond how it is orgonized. @ Predict Usethetoblelo predictwhototoms properties oscolcium. wouldhovesimilor chemicol Wrile theirnomes.

Molecules Atoms moy combine with other atoms to form molecules.A molecule is the smollestporticle of o substonce mode of combined otoms thot hos the propertiesof thot substonce.In some molecules, otoms shore electrons.Some electronsno longer go oround iust one otom. They go oround two or more otoms. These otoms ore then bonded tooether in the molecule. Mony substoncesore found in noture os molecules, not os single otoms. Air is o mixture of severol kinds of molecules.It hos oxygen molecules,nitrogen moiecules,and moleculesof other goses.Most oxygen molecules in oir hove ot leost two oxygen otoms. Nitrogen molecules olso hove h,yootoms thot ore bonded together. Most of the oir in the otmosphere is nitrogen gos. When nitrogen gos is cooled to -196"C, it turns into o liquid. Even so, its molecules still contoin two otoms bonded tooether.

An oxygenmolecule hostwo ofroms.

A nitrogenmolecule hostwo olroms.

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LOmpounos A compound is o type of motter mode of o combinotion of elements. Atoms of the elements ore combined into molecules.Most things thot you see oround you ore compounds. Every molecule of o compound hos the some combinotion of elements. Toke woter, for exomple. Every woter molecule has the some three otoms.

Imogesof Molecules No microscope con enobleo personto ocluoilyseeon otom or molecule.Atoms ond molecules ore too smollfor thot. Speciol technologyletsscientists moke imogesof otomsond molecules. Thistechnologydetects the shopeof on otom or moleculeond then drowso pictureon o computerscreen.The picturesdo not hovetrue colors.Afomsond molecules ore oftenseento be well-ordered, os in thisportof o grophitemolecule.

join iogether Corbonotroms to form grophiie,whichis usedin pencils.

Propertiesof compoundsore different from the propertiesof the elementsthot moke them up. Woter,for exomple is o liquid. At room temperoture,hydrogen ond oxygen ore invisible gosesond do not hove o smell. Sugor is olso mode of otoms of hydrogen ond oxygen, but it olso contoins corbon otoms. Purecorbon otoms con be seenos grophite, or pencil leod. Glucoseis o kindof sugorwith the Pencilleod surely doesnot tostesweet!Yet, when thesethree elementsore combined in the formuloCuH,rQ,Themodelshowsone Howmony form of theglucosemolecule. right woy, they form o sweet,white solid.

Chemicol Formulqs

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Every compound hos o nome ond o formulo. A formulo shows how mony otoms of eoch element ore in the compound. For exomple, woter has the formulo H2O. The "2" after the "H" shows thot o molecule of woter hos two hydrogen otoms. The O stonds for oxygen. It does not hove a number ofter it. This meons thot o woter molecule hos one otom of oxygen. A corbon dioxide molecule hos the formulo COr. It hos one otom of corbon ond trvo otoms of oxygen. Corbon dioxide does not burn. In foct, it con be used to put out fires. At temperotures of -78'C, corbon dioxide becomes o white solid colled dry ice.

ore in this otomsond whoi elements molecule?

Everywotermoleculehostn o hydrogen otomsond one oxygen olom,

ยกf Cnecfpoin! In o formulofor o tellyou? compound, whotdo lhe numbers

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dry ice,liquidnilrogen,or othervery cold moteriqlsore used.Moke o posferto show whol you hove leorned.

Dry iceis frozencorbondioxide.Dry ice sublimotes os it worms.It chongesf,o corbondioxidegos.

351

Kinds of Sqlts Compounds ore not olwoys formed by shoring electrons. Solts ore compounds in which porticles ore held together by opposite chorges. These porticles moy be chorged otoms or $roups of otoms. Porticles with more electrons thon protons hove o negotive chorge. Porticles with fewer electrons thon protons hove o positive chorge. There ore mony kinds of solts, but they oll hove some things in common. They oll hove ot leost one kind of metol element ond one kind of nonmetol element. AII solts con form crystols. Crystols ore formed when chorged porticles orronge themselves in o regulor geometric pottern. Solt crystols ore brittle. Generolly, very high temperotures are needed to melt solts.

Toblesoltis sodiumond chlorine.Its crystolslook like cubes.Its formulois NoCl.

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Table salt

Properties of Solrs Properties of solts ore different from the properties of the elements thot went into moking them. For exomple, most toble solt is mode of sodium ond chlorine. Both of these elements con be very dongerous. Pure sodium is o soft, silver metol. Putting o lorge piece of sodium in woter con couse on explosion. Pure chlorine is o yellow, poisonous gos. Yet together, sodium ond chorine moke o brittle, white solid thqt we con sofely eot.

Purechlorine gos in o boitle.

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Purecopperis o golden brownmeiol.It coneosily be bentto form pots.It con be modeintowires.

Puresodiumis o softmetol. Coppermokeso greensolt whencombinedwith chlorine ond woier. Coppersohsore brittle.Theyconnotbe bent or modeinlo o wire os pure coppercon,

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l. Comporetoblesoltwith gtucose.

Whencopperis usedto mokeo solt, its properties chonge.Coppermokeso bluesoltwhencombined with sulfurond oxygen.

2. Write o porogrophthot teflshow the words moffer, element,atom, crystal,compound,ond molecu/erelole. ¡. @ pred¡ct Supposeo lorge olom bondswirh o smoll otom. Prediclwhetherthe propertiesof the new molecule will be the someos lhe lorgeotom,thesomeos the smoll olom, or differentf rom both otoms.

353

Lesson 3

How do phase changes occur? A maturtalis a solid,liquid,or gas because of the arrangementand motionsof its atomsor molecules.

Solidsond Liquids In Chopter Z you leorned thot woter hos three forms. Woter is o solid when it's frozen os ice. Woter is o liquid in the oceons. In the oir, woter is o gos. These three forms ore colled phoses, or stotes, of motter. The stote of o moteriol ot room temperoture is o physicol property. The phose of woter or ony moteriol is due to the motions ond orrangements of its porticles-its molecules or otoms. The porticles ore olwoys moving. Solids hove o deĂąnite shope ond volume. The porticles of o solid vibrote in ploce. In most solids, the porticles ore very close together. As o solid worms up, it melts. Forceshold the porticles foirly close to one onother, but they con move obout. Therefore, liquids do not hove their own shope. They toke on the shope of their contoiner. Since the forces keep the porticles close to one onother, liquids hove o definite volume. As liquids get colder ond freeze,their porticles slow down ond vibrote in ploce. A moteriol freezesof the some temperoture cÂĄtwhich it melts. This temperoture is colled the freezing point or melting point. For exomple, fresh woter freezeswhen its temperoture lowers to 0'C. Ice melts when its temperoture rises to 0'C ond more heot is odded.

354

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Lesson3

How do phase -occur? changes A materialis a solid,Iiquid,or gas because of the arrangementand motionsof its atomsor molecules.

Solidsond liquids In Chopter Z you leorned thot woter hos three forms. Woter is o solid when it's frozen os ice. Water is o liquid in the oceons. In the oir, woter is o gos. These three forms ore colled phoses, or stotes, of motter. The stote of o moteriol ot room temperoture is o physicol property. The phose of woter or ony moteriol is due to the motions ond orrongements of its porticles-its molecules or otoms. The porticles ore olwoys moving. Solids hove o definite shope ond volume. The porticles of o solid vibrote in place. In most solids, the porticles ore very close together. As o solid worms up, it melts. Forceshold the porticles foirly close to one onother, but they con move obout. Therefore, liquids do not hove their own shope. They toke on the shope of their contoiner. Since the forces keep the porticles close to one onother, liquids hove o definite volume. As liquids get colder ond freeze, their porticles slow down ond vibrote in ploce. A moteriol freezesof the some temperoture ot which it melts. This temperoture is colled the freezing point or melting point. For exomple, fresh woter freezeswhen its temperoture lowers to 0'C. Ice melts when its temperoture rises to 0"C ond more heot is odded.

354

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The freezing point is different for different moteriols. It is o physicol property thot con be used to help tell whot o moteriol is. The freezing point of o moteriol doesnot chonge, no motter how much moteriol you hove. The freezing point of o liquid moy chonge when things ore odded to the liquid. For exomple, the freezing point of solt woter is Iowe¡ thon the freezing point of fresh woter.

ChongingSize Moteriols chonge sizewhen their temperotures chonge. The moteriol is not mode o¡ destroyed. The hotter o moteriol gets, the foster its porticles move. Fostermoving porticles generolly hove more spoce between them. This odditionol spoce cousesthe moteriol to get o little lorger. For exomple, putting o metol jor lid under hot woter mokes the lid hotter. The lid will get o little lorger ond you con remove it more eosily. ..--.. When moteriols cool, they moy become o little smoller. Their porticles move more slowly, ond there is less spoce between them. Porticles never get cold enough to stop vibroting, though. chonge I . úCnectppint, Why do moteriols sizewhentheychongetemperoture? 2 @whymightyou pointof o themélting wontfo consider for substonce beforechoosingmoteriols fryingponsor engineports?

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liquids qnd Goses Compored to solids ond liquids, porticles of o gos ore very for oport. Gos porticles generolly do not offect one onother unless they collide os they move. If o gas is ploced in o contoiner with no other goses,the porticles will spreod out evenly throughout the contoiner. Therefore, o gos does not hove o definite shope or volume. Gosescon be squeezedmuch more thon solids or liquids. This is becouse there is more spoce between gos porticles.

Evoporofing qnd Boiling Evaporotion occurs when porticles leove o liquid ond become o gos. Porticles evoporote from the surfoce of o liquid when they move upword with enough speed.This is how woter puddles evoporote. If the temperoture of o liquid is high enough, porticles throughout the liquid will evoporote too. As gos porticles move quickly upword through the liquid, bubbles of gos form under the surfoce of the liquid. The boiling point of o Iiquid is the temperoture ot which Iiquid turns into gos bubbles. The boiling point is o physicol property of o liquid. The boiling point will be the some for o liquid no motter how much is being heated. Different liquids hove different boiling points. The boiling point con be used to help tell whot on unknown liouid is.

At the boilingpoint, liquidunderthe surfoceturnsinlo gos.Thegosforms bubblesthot riseto the surfoce.liquid olsoturnsfo o gos ot the sufoce.

When o liquid tums into o gos,the gostokesup more spoce.This doesnot meon thot goseshove more motter thon liquids. Thereiust is more spocebetweenthe porticles of o gosthon betweenthe porticlesof o liquid.

356

Wolrervoporis invisible. Whenyou seesĂźeom, whot you ore octuolly seeingore liny woler dropletsformedby ' condensoiion,

Porticles of liquidscon evoporofeevenif the entire liquiddoesnot reochthe boilingpoint Thisis why wet clolhescondry.

Condensqtion

If thegos touches o coolsufoce, condensoiion con (xcur.

'&"s#ew ts*

Condensotionoccurswhen o gos turns into o liquid. This often hoppens when gosporticlestouch o cold surfoce ond their temperoturedrops.The porticlesslow down ond ore tropped by the ottroctive forcesof the surfoce. As more ond more gosporticlesget tropped, they form o liquid drop. The cloudsin the sky ond dew on the ground form by condensotion.

Lntorne

wiF

$lerql 9t'ee!ipci'!, l. Comporethe molionond spocingof porticlesos o moteriolcools from o gos to o liquidond thento o solid phose.Do porticlesever stop moving? 2. Defineond comporeboilingpoints,meltingpoints,ond freezrng DoÂĄnls. Moke o posterwith picturesor o Venndiogrom lo showhow solidsond liquids,or liquidsond gosesore olike ond different.

357

Lesson 4 .r.r

-r.|

What aĂ?e mlxtures

andsolutions? Sometimeselementsand compoundsare mixed togetherbut are not bondedtogether.

Mixtures In o mixture, different moteriols ore ploced together but do not bond to form compounds. Generolly, the different moteriols keep their own properties.If solt ond pepper ore put together to moke o mixture, the solt ond the pepper do not chonge their flovors or colors. Most foods thot you eot ore mixtures of different moteriols. Whot is your fovorite food thot is o mixture? The moteriols in simple mixtures con be seporoted becouse they hove different properties. For exomple, o mognet con seporoteiron filings from sond. This seporotion hoppens becouseiron hos the property of being mognetic, ond sond does not hove thot property. A screen filter con be used to seporote o mixture of pebbles ond sond.

l. Themixtureof solt,pepper, ond woteris pouredthrough o filter.The pepperconnot90 throughthefilter PoPer.

-I

t@ -

Seporoting o Mixture Supposeyou hove o mixtureof soltond pepperthof you wont to hove seporoted. Youcon do this by usingthe different nrooertiesof the two moteriols.Solt dissolvesin woter. Pepperdoesnot. Peooerwould f loot on the woter'ssurfoce.

Some metols, such os gold, silver, copper, iron, ond nickel, ore elements.Mony metols ore mixtures of elements. For exomple, steel is o mixture of iron ond corbon. Bross is o mixture of copper ond zinc. Bronze is o mixture of metols, mostly copper ond tin. These mixtures ore colled olloys. The properties of olloys ore usuolly different from the properties of the originol metols. The properties of the olloys depend on how much of eoch metol is used.

3. Toseporolre he soltfrom thewoler,you conusethe differentboilingpoinh of wofยกerond solt.Thisflomeis hotenoughto boil woter.The flomeis nol hotenoughto evoporotethesolt,Thewoter evoporoles ond thesoltstoys in thedish.

2. Thesoltond woier possthroughthe filter poper.

t . f Cnectpoint Nome 5 metolsthot ore pureelements ond 3 thot ore mixtures.

Norrolive In vourscience journol, wrยกfe o story in which o choroctermokeso mixtureof food to eot. Be sureto cleorlvstotethe steos requiredto mokethe mixture.

359

Solutions When dirt ond woter moke o mixture, the dirt will slowly settle to the bottom. When o pinch of sugoÂĄ dissolvesin o toll gloss of woter to moke o mixture, the sugor will not settle to the bottom. Sugor ond woter moke o speciol kind of mixture colled o solution. A solution is o speciol mixture in which substonces ore spreod out evenly ond will not settle. In o solution, the substonce thot dissolvesis colled the solute. The solvent is the substonce in which the solute is being dissolved.In the solution of sugor ond woter, the solute is sugor ond the solvent is woter. Woter con be o solvent in so mony different solutions thot it is colled o universol solvent. When o solute dissolves,individuol particles seporote from the solute ond spreod throughout the solvent. You con moke solids dissolve in o liquid foster by stirring or heoting the solution. Grinding o solid solute into smoller pieces will olso helo it dissolve foster.

Thesesoltcrystolsore modewith the elemenls potrossium, mongonese, ond oxygen.Thesolt leoves purplehoilsos it dissolves in woferond spreodsout.

360

-'":Ă ,;:

-"'-"-*w**5

A smollomount of soluteis being dissolved. It will mokeo dilute solution.

Not oll solutions ore mode by dissolving o solid in o liquid. Two liquids con moke o solution. A gos con dissolvein o liquid. For example, woter in o loke contoins dissolved oxygen ond corbon dioxide goses.Why would it be importont thot these gosesore dissolved in the woter?

Amounts of Solutes

If o solutionis soturqiedno moresolutewill dissolve.

A lorgeomount of soluteis beingdissolved. It will mokeo concentroied soluiion.

Solubility is o property of o substonce. Solubility is how much of o substonce con be dissolved by a solvent ot o certoin temperoture. The hotter o solution is, the more solid solute con be dissolved. Solutions con be describedos being soturoted, concentroted. or dilute. A solution thot is soturoted contoins oll the solute thot con be dissolved without chonging the temperoture" If more solute is odded to o soturoted solution, the solute will not dissolve. A concentroted solution hos so much solute thot it is relotively close to being soturoted. A dilute solution is far from being soturoted. In mony coses,o moteriol will not dissolve ot oll in o porticulor liquid, no motter how hot it is. For exomple, solt will not dissolve in oil.

.ĂşLe"sotr Checkpoint.. 'l . Couldo mixtureof pepperondwoterolsobe colledo solution? Couldo mixture of soltond Exoloinvour woterolsobe colledo solution? onswers. 2. How conyou couse.more solidsoluteto be dissolved in o liquid?

3 E@EE&@

DescriptiveObserve the

piclureson thispogethotshowthe mokingof o soturotedsolutionof woter ond o ourolesolt.In your sciencejournol, write o descriptionof the solution'soppeoroncein eoch of the photos.

zo Investigofe Whot bootdesign will corrythe mostcorgo? Thinkobout whot you know oboutdensityond the other propertiesof motler. Designond buildo bootihot con corry o lorgeomountof corgowithoutsinking.

Whol to Do

Moleriqls

,:& foil ond cloy

't tub with woter

The Problem Designo boot fhot will supportthe mostcorgo possible.Foil,cloy, or onothermoleriolof your choicecon be usedto build the boot. Considerwhich moteriolwould be besl. Considerdifferentboof designs.Sketchor diogromyour proposed designchoice.Exploinwhy you pickedyour designsolution.

Identifywhich moteriolswill work bestfor your design. Moke o plon or o procedure.

metricruler

your model boot.Meosureits length, Construct width, ond heightin centimeters. pennres

bolonceond grom cubes

Youmeosured mossusing ond nonslondord slondordunits. Penniesore nonstondordunits of moss.Groms ore stondordunifs.

Testyourbootdesign.Flootyourmodelbootin the yourboot tub of woter.Predict how monypennies to yourboot.Record will hold.Add corgo(pennies) you odd beforeyourbootsinks. the numberof pennies

@ Ur" o bolonceto meqsure themossof thecorgo in groms.Recordthe moss. '*----.

Didknowingoboof densifg helpgor.tsolvegoondesign pnoblern? Fxploin.

-:-...'-

Amounl of Corgo Corried WiĂşout Sinking (number of pennies) lenoth

width _

h e i g h_ t

oroms

If goonboof wos domoged, how cottfdgounepoirif? Whofwoofdgouose?

Exploin Your Results I . Sketchyour modelboot design.Exploin whot cousedyour boot to sink. 2. Inferpref Dqfq Evoluoteyour modelboot design.Wos it moreor lesssuccessful thon the designsof theothergroups?Exploin. 3. Whot shope,size,ond moteriolmodethe boot thot couldcorry the mostcorgo?

Reviewyour procedureond designwith otherstudents. Comporeond controslyour investÂĄgotion with theirs. Ask yourselfond the other sludentsqueslionsobout how your procedureond design couldbe improved.Usetheir comments to helpyou moke revisions.

In eoch line plot, noticehow the doto spreodsout on ihe numberline.Noticeolsohow it clusters in certoinoreos. Thenusethe tobleond the lineplotsto onswerihe quesfions.

In whichtemperoture rongedo themeltingpointscluster? A. -,l20'C to -80'C

B. -贸0'c to-20'c C. -40'C ro0"C D. 0'c ro20"c

rongedo the boilingpointscluster? Q) In whichtemperoture

F. G. H. I.

I 贸0'C to 200'C 80"Cro 140'C 0'c to 40'c *80'C to -40"C Q

Wni.n of theliquidshoson extremely high meltingpoint,comporedto the others? A. propone B. chlorine C. iodine D. hydrogenperoxide

In whi.h temperoture rongeis the

greotest gop betweenboilingpoints f o r t h e s el 0 l i o u i d s ? ,l20'C ,l85'C F. between ond -33'C ond Z9'C G. between H. between17"Cond79"C ,l20"C L between100'C ond

Copy the lineplotson lhe previouspoge. Findthe meltingpointond boilingpointfor 5 other substonces. Moke o toble ond odd the doto to the lineplots.

Use Vocqbulory orom {p.348)

eleclron (p. 3a9)

compound (p.351)

elemenl (p. 343)

i Exploin Concepts ro.Explointhe differencebetweenon otom ond o molecule.

neulron (p. 3aB)

concentroled (p.3ó1)

proton (p. 348)

dilure (p.3ó1)

soturoted (p. 3ó I )

I l . Whot is the differencebetweeno mixture ond o solution?

12. Exploinhow motlerchongesf rom o solid to o liquidond thenlo o gos.

Usethe termfrom the listobove thot besl completesthe sentence. I.

A(n)is in the nucleus of on otom ond hoso positivechorge.

A(n)is in the nucleus of on otom ond hosno electricol chorge.

Alnl is oort of on otomond hoso negotiveelectricolchorge.

A solutionis if it hoso lorge omountof solutein comporison with the omounlof solvent.

A(n)solutionhoslittlesolutein comporison with the omountof solvent.

A solution is if it contoinsoll the solutethot con be dissolvedot the time.

Thereore morethon 100 typesof motter, eochcolledo(n)

Thesmollest porticleof on elementis o(n)

Elements combineto formo(n)

I3. Infer Youmix oil ond vinegorfor o solod theoil hos dressing. Aftero few minufes, seporoledond is flooting.Inferwhich hosthe greoterdensity-oilor vinegor. Exploin. Usethe followingtoble for QuestionI 4.

HeldTogether by Opposite €horges

chloride Clossifywoterondsodium (toblesolt)by tellingwhichcolumn eoch in. belongs

15. Form Gluestions You hoveo divided box with lobeledcomportmenls. Eoch comportmenihos o sompleof o different element.Youdrop the box ond spill oll lhe sompleson the floor. Formquestions to help you put lhe elementsbock in the right comporfments.Formot leostfour questions.

1 7 . Which of the followingis o mixture? @ @ @ @

gold steel iron nickel

r8.Theomountof motlerin on object is its

@ Predict y

TestPrep

l贸. A plosticblock hos sidesthot meosure 4 centimeters, 2 centimeters, ond 3 cenfimelers. Its mossis 19.2 groms. Predictwhetherthe blockwill floot in woter.Will it floof in olive oil? Gother informotionbeforemokingyour predictions.Fill in the boxesoerow. Informolion

H)-

@ @ @ @

weight. densily. volume. moss.

| 9. Exploinwhy the onsweryou selecfed for QuestionI B is best.For eochof the onswersyou did not select,give o reoson why it is not the beslchoice.

; 20. E@@Descriprive Chooseon itemf rom lhe clossroomono describeot leostfive physicolpropefies of the item.

96?

-l

Theworstgrode Noncy Hollevergot wos in science.Shewos in fourthgrode. Shethoughtsciencewos boring.Thotchonged in sixthgrode.Ms. Holl hod o wonderfulscience ot teocherwho inspiredher to do experiments home.When shegot older,shestudiedspocesciencel| ot NASA. in college.Now sheis o reseorchscientist S h ed o e sr e s e o r cohn f l u i d s - g o s e so n d l i q u i d s . r\qncy KqDer Holl nqn NoncyRobel She leornshow they behovein spoce. workswilhooses in whichfluidss Ms. Holl conducts ondliquids'""perimenis for the moment,to be weightless,os they *orl多 u"J'l ore doneot NASA ond ore spoce.Theseexperiments ensurethot repeotedmonytimes.In thiswoy, scientists moy be Thenthe experiments ihe resultsore consistent. repeotedin spoce-on rockets,on the spoce SpoceStotion. shuttle,or ot the Internoiionol for Ms. Holl lovesworkingos o spocescientist NASA. Butwhen shefirstwent to college,shestorted M. s . H o l l o u t i n c o m p u t epr r o g r o m m i n g switchedto spocescience,becousethot is whot shereollvwontedto do. Sheodvises young peopleto work hord to pursuetheir interests. strongest

Observehow dropsof woter interoct.Fill on eyedropperwith woter.Counthow mony dropscon fit on o pennybeforethe woter overflows.

2Mg *

f,P Mognesium

370

------>

2MgO

_**-

'e "t' Oxygen

MognesiumOxide

â&#x201A;Źho&r f? V*ahulory physicolchonge poge325

chemicol chonge poge375

combustion pose377 reqctqnl

product

poge3ZB

pose328

chemicql equotion poge328

polymer

pose388

Explore Whotconhoppen Weonsofetg duringo chemicolchonge? goggres. Moleriols

Whql to Do Put50 mLof woter ond o thermometer in cuo A. After 1 minute,recordthe temperorure.

2 cupsond poper towel

ffi w:l room+emperoture woter ond groduotedcylinder

Add 3 Alko-Seltzer@ toblers to cup A. Woit I minute. Recordthe temoeroture. Donof tosfe fhe toblets, the powdens,on fhe liqrids.

J:l.!*;.*多

lhermometer ond 3 Alko-SeltzeP ioblets

\."

Wipe off thethermometer witho popertowel.Put50 mLof woterond thethermometer in cupB. After 1 minute, recordthetemperoture.,.

端

\s*

cupwith 3 spoonfuls of bokingsodoond cupwith 3 spoonfuls of colciumchloride

Add thebokingsodoondcolcium chlorideto cup B.Woit I minufe. Record thetemoeroture.

a :

timeror stopwotch {or clockwith o secondhond)

After you collect dotc, you usepost experiencelo help evoluolethe doto ond mokeoccurote inferences.

If o neocfionprodocesheof,fhe fempenofone rises.Thenmol enenggis givenoff. Lessenenggnenroins. Bgosingo thenmornefen fo rneosone fhe ternpenofone chonge,gooconfell if enenggis losf on goineddoningo neocfion.

ExploinYour Results Usethedofo you collected io mokeon inference.In whichreociionwosenergylost?

.r t!.¿

¡"¿?nlDrow Conclusions Yoursciencebook is pockedwith focts.You put thesefocts togetherwith your own knowledgeoboutthe world to drqw helpsyou shorpenyour conclusions. Drowingconclusions of science. understonding . Reodthe foctsoresented in this orticle.

r Thinkoboutwhotyou olreodyknowoboutthetopicto moke qn inference oboutit. o Usethe sciencefoctsond your own knowledgeto drow o conclusion. Cooking Article

OcldngErocü Bokersuseyeostto boke breod.They mix the yeostwith worm woter ond sugor.Then they odd flour. The yeostdigeststhe sugarond gives off bubblesof corbon dioxide. This mokesthe breod dough rise. The heot of boking kills the yeost. Look ot the holes in q slice of breod. Whot conclusion con you drow obout it thot

relotesto the yeostond its octivity? iri{{{rr.a{r, | ,{i},,*rr:r} ,¡

Apply It! Foct Moke o grophicorgonizer likethe one shownhere. Write down your conclusion. Listthe foctsfrom the orticre Focl

ffi-

tttl

onoyourown Knowreoge thotledyouto drow this conclus¡on.

ffla

Conclusion

{DY@rAmeThereg With oir tonks stropped securely to your bock, you swim down 40 meters toword the oceon floor. It is dork, but you hove o floshlight. You cost its beom on o sunken ship, lying tilted ot the bottom of the oceqn. The ship hos been here for over six decodes.It hos chonged o greot deol since it sonk. The once sturdy wood is soft with rot. The metol no longer gleoms but flokes with rust. The oceon is slowly chonging the moteriols

Lesson I

What aĂ?echemical changes? Matter changesall the tĂme. Somechangesare physical chanoes.Othersare chemicalchanaes.

Physicolond ChemicolChonges Motter con undergo physicol chonges ond chemicol chonges. When o physicol chonge hoppens, the moteriol remoins the some. Some physicol chonges ore changes in position, size, shope, volume, ond phose of motter. For exomple, falling roindrops con freeze to form sleet. Even though the roindrops ond the sleet differ in size, shope, volume, ond phose of motter, they ore both still the some essentiolsubstonce:woter. On the other hond, o chemical chonge hoppens when one substonce or kind of motter

changesinto qnother completelydifferent kind of motter with different properties.For exomple, the shipt wheel in the picture wos mode of the element iron. After yeors of being in the oceon's wotet the iron on the wheel's

< #*tr:r*t#H#:."ffi1r' physicol propertiesof rust ore different from those of iron. l.

Whot is fhedifference ..Ăş9,h:g!.Coint, chongeond o physicol betweeno chemicol chonge?

2 EM@DescriPtive

Think of o

time when you've cousedo physicolchonge, o chemicolchonge,or both. Describewhol hoppenedin your sciencejournol.

Thisship'swheel hosundergone chemicolchonges.

Evidenceof ChemicolChonge

.rrra?t?ยก:-.

Corsrustwheno chemicolchongeturns shinyiron into dull brownish-red rust.

Thisontocidtobletgives off corbondioxide gos os it undergoes o chemicolchonge.

When o chemicol chonge occurs, otoms reorronge themselves to form different kinds of motter. It is not olwoys eosy to tell if o substonce hos chonged chemicolly. Somesigns thot o chemicol chonge hoppened ore o chonge in color or thot o gos or o solid formed. As you hove reod, iron undergoes o chemicol chonge when it rusts. A sign of this chonge is the change in color-the groy metol turned brownish-red. Dropping some kinds of ontocid toblets in woter olso results in o chemicol chonge. The toblet fizzes,giving off mony tiny bubbles. Thesebubbles ore corbon dioxide gos. A solid ontocid toblet does not contoin gos. This gos forms when the compounds in the toblet undergo chemicol chonge. The pictures below show on experiment in which a "tree" mode of copper wire is dipped into o solution. Note how the tree chonges. Crystols form, clinging to the wire bronches. The formotion of this solid materiol is evidence thot o chemicol chonge hos token ploce.

Theburninglogsgive off heatond lightos o chemicol chongeis occurring.

Thesecopperwires hovebeenorrongedin theshopeof o leofless evergreentree.

376

coPPer hee is ploced inlo o solution of chemicols.

ChemicolChongesond EnergyGhonges During some chemicol chonges, bonds between otoms or moleculesbreok. During other chemicol chonges,new bonds form. The formotion ond breoking of chemicol bonds olwoys involves the moteriols toking in or giving off energy. Sometimes, we con observe these energy chonges os they occur. For exomple, o log burning in o fireploce is undergoing the chemicol processof combustion. During combustion, the burning log gives off energy. We detect the energy os the heot ond light of the fire. In other reoctions, energy moy be given A chemicolchongehos off in the form of electricol enerqy. cousedsolidcrystols to form on thecopper ยกf L."sott checkpoint, hee.Thesecrystolsore l. Lislthreetypesof evidence of chemicol chonge. modeby o chemicol 2. Comporethesecondond thirdpiclures of thecoppertree chongethot hoppens experiment. Asidefromtheformingof solidcrystols,whot with fie copperond o otherevidence of chemicol chongein theliquiddo yousee? chemicolin the solution. '@ look ot thetop of fie Drow ConclusionsWhenyou cookon egg,do you 3. tree.Why hosn'tit thinko chemicol chongeoccurs? Why or why nof? chonged?

377

Lesson2

rffhat aresomekinds of chemical reactions? Chemicalchangesoccur during chemicalreactions. Thereare severaldifferent kinds of chemicalreactions.

Chemicql Equotions During o chemicol reoction, one or more substonceschonge into other substonceswith different chemicol ond physicol properties. A substonce used in the reoction is colled o reoctont. A substonce mode during the reoction is colled o product. During the chemicol reoction, the reoctonts undergo chemicol chonge. Their otoms reorronge to produce the products. A speciol kind of "sentence," colled o chemical equction, shows whot hoppens during o chemicol reoction. The reoctonts ore listed on the left side of the chemicol equotion. Ihe products ore listed on the right side. An orrow between the reoctonts ond products is sometimes reod os "mokes." It is similor to on equol sign in o moth equotion. In the picture ot the right, electricity flows through woter. This couses the otoms in the woter molecules to reorronge ond form hydrogen

ond oxygen goses.Woter is ihe reoctont.Hydrogenond oxygen gosesore products.The equotion for this reo reoction is: 21120

co tL,

_____> 2H,

eb.

Hydrogen

Reoclonls

378

Products

a 't Oxygen

Testtubes collect bubbles.

Mognesiummetol is groy.

2Mg

concombine Mognesium with oxygen.Theyore reoclonts.Brightlightond heotshowthoto reqction is hoppening.

Theproductis mognesium oxide.Thisproduclhos propertiesthotore different from the propertiesof the reoclonls.

2MgO

^n,il*d

@.*?

{Ăź

*d,

Mognesium Reo(lqnts

Oxygen

MognesiumOxide

Producl

Mognesium is o groy metol. If it reocheso high temperoture, it reocts with oxygen in the oir ond burns with o bright white glow. In foct, mognesium is often used in fireworks. As the chemicol reoction goes on, o white powder forms. This powder, mognesium oxide, is the Droductof the reoction. t,1

Motter Is AIwoys Conserved Motter connot be creoted or destroyed during o chemicol reoction. This stotement is colled the Low of Conservotion of Moss. It meons thot the totol moss of the reoctonts equols the totol moss of the products. If you boke o coke, for instonce, the moss of the ingredients equols the moss of the coke plus the moss of the woter vopor, corbon dioxide, ond other troce gosesthot floot from the oven, moking the coke smell so good.

Motler is when conserved you bokeo coke.

equotions show? I . ĂşCnecrpoint-:Whot do chemicol equotionon theto'p Lookot thechemicol 2 EM@ youstortwith 100otomsof mognesium. of thispoge.Suppose How mony molecules of oxygenore neededto reoctwith o the moonesium?

379

Types of Chemicol Reqcfions It is sometimes eosier to understond chemicol reoctions if you use o model. A model is something thot stonds for o reol thing. We con use models to leorn something obout reol things. We con use trucks ond troilers os models of otoms in reoctions. Three kinds of chemical reoctions ore described here.

Breoking Aport, Joining Together, Switching PIoces In one kind of reoction,compoundssplit oport to form smaller compoundsor elements.This is colled o

Whensugor is heocd, it furnsinto coromel.During port of this decomposition reoction,sugor molecules breokoport.

decomposition reoction. To picture o decomposition reoction, think of o truck unhitching from the troiler. This is the kind of reocĂźon on poge 378. In this experiment, electricity couses woter to breok oport to form hydrogen ond oxygen goses. In onother kind of reoction, elements or compounds come together to form new compounds. This is colled o combinotion reoction. To picture o combination reoction, think of o truck connecting to a troiler. This kind of reoction occurs when iron ond sulfur come together to form o compound colled iron sulfide.

BeforeĂşe combinotion reoclion,iron is o grey mogneticmoteriol.

Sulfuriso yellowpowder lhot is nof mognefic.

In o third kind of reoction, ot leost one molecule splits oport. The ports of the molecule switch ploces, iust os two trucks con switch trailers. This kind of reoction is known os o replocement reoction. One exomple of o replocement reoction is the burning of o condle. Some condle woxes ore long molecules of corbon ond hydrogen otoms. Remember thot oxygen gos is o molecule mode of two oxygen atoms. When wox burns, the long molecules ond oxygen molecules breok oport ond rejoin in new comoounds such os corbon dioxide ond woter.

A replocement reoclion occurswhenwox burns. X[ Lesson Checkpoint,, l. Describe threekindsof chemicolreocfions. 2. In the chemicolreoctiondescribedon poge 379, mognesiumreocfswith oxygengos. Whot kind of chemicolreoctionis this?Exoloin.

Wheniron ond sulfurore heotedtogether,they reoct.

imogeofthe 3 E@Besidesthe truckond troiler,whotothermodelsfor reoctions con be used?Drowoictures to showhowyourmodelworksfor reoctions. |wo differentkยกndsof chemicol

Afier they reocl,iron ond sulfurmokeo compound thot is not mognetic.

Lesson3

How arechemical properties used? f,

Chemicaland physicalpropertiesare helpfulin many ways.Theycan be usedto separatemixturesand to help identifumaterials. Ihe fossildoesnot reoctquicklywith vinegor,but the limesione oround thefossildoes. Whot evidenceof thisreoctioncon you detect?

Seporoting Mixtures Substoncesin some mixtures con be seporoted by physicol meons. As you reod in Chopter 11, you con seporote solt ond pepper becouse they hove different physicol properties. Substoncesmoy olso hove different chemical properties thot con be used to seporote them from one onother. Scientistswho study dinosour fossils ond other fossils use chemicol properties to seporote mixtures. Fossilsore often scottered throughout limestone. It con be difficult to chip limestone off o fossil without domoging the fossil. However, limestone con be dissolved by vinegor. A bubbling reoction occurs. Fossils,which ore mode of

o different kind of rock, do not reoct with vinegor os quickly. Soscientistssometimesuse vineooror similor chemicols to seporote fossils from rock.

Seporoting Metols from Ores " Oresore rocksthot include metols combined with other substonces.Peoplerely on chemistryto releosemetols from their ores.For example, iron ore contoins iron oxide. Heoting iron ore in a hot furnoce with solid corbon ollows the iron to seporotefrom the oxygen in the ore. The result is pure iron ond corbon dioxide. This processworks becouseiron hos the chemicol property of bonding to oxygen lessstrongly thon to corbon.

382

In thisblostfurnoce,iron is seporotedfrom iron ore.The processrelieson thedifferent chemicolpropertiesof fte substonces heoยกedhere.

Sometimes chemicol properties con be used to seporote elements from solutions. For exomple, leod con be token out of o solution thot contoins woter, leod, ond other moteriols. The solution is poured into o contoiner with o secondsolution thot contoins iodine. Both solutions ore cleor liquids. As soon os the solutions mix, the leod reocts with the iodine. These tlvo elements form o compound colled leod iodide. This is o yellow solid. The leod iodide con be filtered out of the liouid to remove the leod from the solution.

Thissolutioncontoins o leodcompound. properties Chemicol conbe usedto removethe leodfrom thesolution.

Thesolutionis pouredinto o secondsolutionthot conf,oins o compoundof iodine.

Theleqdcombines with the iodineond formso yellowsolid.Thissolidcon be filteredio removethe leodfrom fhe solution.

ĂşCnecfpoÂĄnt, How con chemicolpropertiesbe usedto seporotesubsfonces in o mixture or comoound? ''@ 2. Dro* Conclusions The chemicolreoctionfor purifyingiron ore lookslikethis: t7

2FeO+C'2Fe+CO2 iron corbon iron oxide

corbon dioxide

Reviewthe differentkindsof reoctions discussed in Lesson 2. Whot kindof reoctionis shownhere?

383

Idenrifying Substqnces

Fruitssuchos oronges ondlemonscontoinocid.

Soopsmoy confroin boses.

Scientistsusephysicol properties,such os density,to identify substonces.They can usechemicol propertiesfor this purpose,os well. The picturesbelow show one woy scientistsdo this. Acids ond bosesore two common typesof substonces. Lemon iuice ond vinegor ore ocids.Householdcleonersmoy contoin bases.Strongocidsor boseswill reoctwith other moteriols more eosily thon weok ocidsond bosesdo. Acids ond boseshove chemicol propertiesthot help peopleidentify them. Acids ond boseseoch reoctwith chemicolsin speciolpoper colled universol indicotor poper.Thesereoctionsproducecolor chongesin the poper. Substoncesthot are strong ocidswill turn the poper red. Strongboseswill turn the poper purple. Weokerocidsor boseswill producedifferent colors.Other kinds of popers ond liquids will chongecolorsbecouseof ocidsor boses. You cannot identify o substanceiust by using universol indicotor paper or similor products.Mony different ocids will turn indicotor poper red. Mony boseswill turn it purple. Indicotor poper is helpful, though, in providing more clues for peopleto usein identi$ring o substonce.

Rqinbow Strip of Indicotor Poper Bosescquseuniversolindicotorpoperto turnshodes of green,blue,ond purple.AcidsmokeĂşe poperturn orongeor red.

H):drochloric acid

Tapwater

r:!

Borium chloride

Strontium chloride

Colcium chloride

Scientistssometimes use flome tests to identiff o substonce. In o flome test, o moteriol is heoted to high temperatures in o flome. Different substonceswiII couse the flome to hove different colors. When these flomes ore studied closely with loborotory equipment, the substoncescon be identified. Whot color flome does colcium chloride qive off? yf Lessoncheckpoยกnt,

Potrossium chloride Thesewireswere dippedin different metolsolts.When the metolis heotedto o high the fremperoture, colorof theflome con be usedio identifythesolt.

fhe followingcompounds: strontium l. How mighto scientist distinguish chlorideond ootossium chloride? 2. Whot color do you thยกnkindicotorpoper would turn if it were dipped in shompoo? Exploinyour onswer.

3 g!@ffiFiDExpository

Usewhoiyouleornedobout

thotcontoinstrontium ond flometeststo exploinhow compounds in boriumcould be usedin fireworks.Write your explonotion your sciencejournol.

lemonjuice fromoiojuice

Liquidsoap

seowoler

household ommonio

Householdcleaner

385

Lesson 4

Howis chemicaltechnology usedin our lives? (

Chemistshavemadeimportantdiscoveries that haveimprovedhealth, nutrition,agriculture,transportation, and manyotherpartsof our lives.

Chemistry qnd Heqlrh Antibioficsond othermedicines ore oftenin copsules. The copsules ore mode of chemicols thot dissolvein your digeslivesystem.

Monyvitominpills todoyore mode by chemists.

Yeorsogo, people sometimes died from simple cuts. If o cut become infected with bocterio, the infection could spreod to the blood. This kind of infection wos very serious. No medicine could cure it. In 1928, British scientist Alexonder Fleming mode on occidentol discovery. It eventuolly led to the development of very powerful medicines to treot infections. Fleming grew bocterio in dishes. When mold grew on one of his dishes, Fleming noticed thot the bocterio neor the mold died. The mold produced a substonce thot killed the bocterio. Fleming colled this substonce penicillin ofter the nome of the mold. Chemists seporoted penicillin from the mold ond found ways to moke it. Mony kinds of infections could be treoted with penicillin. By the mid-l940s, this chemicol become o medicine thot soved mony lives. TodoÂĄ mony other medicines olso kill bocterio. These medicines ore colled antibiotics.

)

BocĂźerio ore growingin o petridish. !!

Chemisrryond Foods Yeorsogo, somepeoplesufferedfrom o diseosethot ot first mode their skin turn red ond scoly.Other peoplesufferedfrom o diseosethot mode the tonoue smooth. Another diseose gove children bodly formed bones, including legs thot bowed out or knees thot knocked together. In the eorly 1900s, scientists found thot eoch of these diseosescould be preventedif people ote certoin foods. Chemists identified the substoncesin foods thot prevented these diseoses.They nomed these chemicols vitamins. Todoy, vitomins ore odded to mony foods thot we eot in the United Stotes.The diseosescoused by lock of vitomins ore now rore in this country. Fertilizers ore chemicols thot formers odd to the soil to increose the omount of plonts thot will grow. In the 1900s, chemists found o woy to moke lorge omounts of fertilizer. Using fertilizers, formers in the United Stoteshove been oble to grow more food thon before. This hos lowered the cost of mony foods.

Different fertilizersodd potossium, nilrogen,ond phosphote to thesoil.These chemicols help plontsgrow.

Bocfrerio con

Mold is ploced in o dishond it olsogrows. L

ffr' ' p' r

Boclerioconnot

surviveneorthe mold.

1|Checkpoin! Whof ore ontibioticsond how hovelhey. improvedheolth?

2 g@ffi@

in Chopter 贸, PersuosiveAsyouleorned

overuseof ontibioticscon cousethemto stop workingto curediseoses. However,mony of todoy'ssoopshoveontibioticsodded to them. Wrile o shorteditoriolon whelheryou thinksoopsthot you useevery Exploinyour reosoning. doy shouldor shouldnot contoinontibiotics.

347

Chemisrry qnd New Mqteriqls Mony moteriols you use every doy come from noture. For instonce, the cotton in ieons comes from o plont. The wool in o sweoter is sheep's hoir. But some ordinory moteriols ore not found in noture. Scientistsinvented them. For exomple, nylon in iockets ond other clothing, plostics in toys ond mony other obiects, ond even concrete in sidewolks ond roods ore oll moteriols thot people mode.

Mqteriqls for Everydqy Use In the 1800s, scientistsbegon working to moke o fiber to use insteod of silk. Silk is strong, soft, smooth, and comfortoble to weqr. To make silk though, people hod to get threods from silkworm cocoons. Thot is one reoson silk hos been expensive. In the 1880s o French scientist mode o soft, shiny fiber that wos like silk. The only problem wos thot it eosily burst into flomes. In the mid-1930s,on Americon chemist reoched success.His silklike fobric, colled nylon, wos perfect for stockings. It soon wos used for moking ropes, nets, fishing line, ond mony fobrics. Nylon is o polymer-o lorge molecule mode of mony iden端col smoller units connected together. In nylon, eoch unit is mode of six corbon otoms, seven hydrogen otoms, ond one Thesolufionin this beokeris drown oul tro nitrogen otom. A polymer moy hove thousonds or millions mokenylonthreod. of units in o single choin. Plostic is onother type of polymer thot scientistsleorned to moke in the loborotory. One kind of plostic molecule hos o long choin of corbon otoms, eoch with two hydrogen otoms. Mony plostics ore mode with chemicols found in petroleum. Plostics ore usefuI becouse they ore lightweight ond longlosting. They ore olso foirly cheop to moke.

Mqteriqls for Building

Plosticis usednol just for moking loys.Thisortificiol heortis modeof metolondplostic.

388

You might think thot concreteis iust sond mixed with woter. But the moin ingredient is cement-o humon-mode moteriol. To moke concrete,cementis mixed with grovel, sond, ond woter. Cementsetsduring o chemicol reoction.The resulting concreteis rocklike-hord ond longJosting.

Chemists hove mode different kinds of concrete to use in different woys. They odd certoin chemicols so concrete con horden in very cold weother. Other chemicols give concrete extro strength. Sometimes lorge omounts of tiny flbers ore mixed in concrete to moke it stronoer ond hove fewer crocks.

Chemistry ond Trqnsportofion

o¡l usephysicolond chemicolchongesin peholeumtromoke monyproducts.

Howeveryou got to schooltoday,by bus, by cor, by bicycle, or even on foot, you hove chemiststo thonk. Advoncesin chemistry hove given us o lorge supply of rubber both for ti¡es ond for the solesof shoes.Noturol rubber comesfrom plonts. It bendseosily ond is waterproof.But untreotedrubber becomes brittle ond crocksin cold weother.It melts ond becomesgooey in hot weother.In the 1800s,chemistsexperimentedwith noturol rubber.By heoting it ond odding sulfur, they mode the rubber duroble ond usobleyeor-round.In the mid-1.900s, chemistsdevelopedo woy to moke ortificiol rubber in foctories. We owe our modern tronsportotion systemnot only to rubber but olso to petroleum,or crude oil. Petroleumis o mixture of mony different compounds.Gosoline,kerosene,dieseloil, ond lubricoting oil ore someof the compoundsin petroleum. Thesecompoundsore seporotedot lorge oil refineries.Gosoline is one of the smoller moleculesin petroleum.Chemistshove developedwoys to breok down someof petroleum,slorger moleculesto form gosoline.In this woy, we con get more gosolinefrom eochborrel of petroleum.

Thegosolinethot mokesthis mofrorcycle trovel ol greoi speed wos seporobd or converiedfrom othercompounds in petroleum. Monyof the bodyportsore modeof plosiic.

Thetiresfor this molorcycle weremode from heotingo mixlure of rubberond sulfur. I t. ,$C,!9c¡p9¡¡tl Howdid scienrists workingwith rubberond petroleumhelp our modernlronsporfotionsystem?

2 @Use fheInternetfo leornoboutreseorch thotscienfists ore doingon superconducfing ceromics for usein very fosl troins(colledmoglevtroins).Summorizewhof you reorn in o porogroph.

Chemislry qnd Technology ra39 ChorlesGoo端eor discovered o processhe colledvulconizotion thot moderubberstronger.

ra59 Thefirst oil well in the United Stotesis drilled.Thefirstoil re{ineryis builtot oboutthistime.

Korl Benzdevelopsoneof the firstcorsthot runson gosoline.

lgtot' Ammoniowos first modewith nitrogenfrom the oir. It wos loier usedos fertilizer.

r9t2a AlexonderFlemingdiscovers penicillin.

t935 Thefirst nylonfiber is modeby qnd his Dr.WolloceCorothers loboroioryieom.

Chemicqls ond Sofety Some chemicols moke life lessdongerous for us. For exomple, scientistshove leomed how to use chemicols, such os chlorine, to kill germs in drinking woter. This sonitotion meosure helps prevent woterborne diseoses.Beforechemists developed modem woter treotment methods, these diseosescoused o very serious threot to heolth in the United Stotes.Woter treotment is one woy chemicols hove improved our heolth ond increosed our sofety. However, when chemicols ore used incorrectly, they

con be o hazard..Youneedto look corefully ot worning labels on chemicols.By heeding thesewornings, you con help protectyourself, your fomily, your pets,ond your home. You moy hove cleoning supplies,such os bleoch, ommonio, oven cleoner,ond others in your home. Beforeyou use ony of these cleonsers,reod the directions. The directions

moy tell you to wear glovesto protect your skin. They moy tell you to weor gogglesto protectyour eyes.They moy tell you to keep o window open for freshoir. This will help protectyour lungs from dongerousfumes thot come from the products. You olso needto be very coreful not to mix ony cleoners,such os bleoch, ommonio, droin cleoners, ond others.Doino so con couse dongerous chemicol reoctions which 'cqn leod to lung domoge, burns, ĂŠxplosions, ond even deoth.

Reodingo lobelcontellyou if the in o bottleis poisonous or subsionce lobels!Theyore there toxic.Respect to profeclyou.

392

-!l

Lobels

Poisonous

Conosive

Flammable

RadioactĂve

l . Why is it importont to ovoidmixinghousehold cleoners? ) Whot is o polymer?

D.orrt ConclusionsOf oll thetechnologicol developments you discussed in thislesson, thinkmostimproved whichonedo humonIives? Exploin.

offecthow longo reoctiontokes? foblel bubblesond f izzeswhen droppedinlo woter. An Alko-Seltzer@ In this octivity,you will find out how lemperotureoffectshow fost lhis reoctionoccurs. Moteriqls

llfh¡r+ to ll¿r Do Whqr l¿r

J CUps -L-

lÑ-

ice-coldwoter, roomJemoeroture woler worm woler **!t

3 Alko-SeltzePtoblets

fü

thermometer ond l¡meror stopwotch (or clockwith o secondhond)

.Whenyou do on octivity,corefully selectwoys to help collect, record, ond repori your dofo. You might wishlo usegrophs, lobles,chorts, diogroms,or drowings.

Drop on Alko-Seltzer@ tobletinto the cup. Meosureond recordthe numberof seconds 'T requiredto completethe chemicolreoction. Repeotsteps1 ond 2 with roomJemoeroture woter ond worm woter.Moke o chortto helpcollect your doto.

To helpcollecf,necond,ond neponfgoondofo, 多seo chont likethisoneon selecto diffenenf toble,chonf,on diognorn.

Wqler Temperqlure

rc)

Room-lemperqture woler

ExploinYour Results 1. Reportthe doto you collecfed. Thinkof o woy to show the timesrequiredto complete Youcouldmokeo bor the chemicolreoctions. g r o p h ,o l i n eg r o p h ,o r o d i o g r o mY . o um o y selecto differentwoy to reportyour doto. 2. Xnfer How doestemperoture offecthow long o chemicolreoctiontokes?

(io Further If you repeotthe octivity severoltimes,will you get similorresults? With your teocher's permission, moke ond corryout o plonto find giveon out.When finished, orol reportio your closs.

You hqve leqrned qbouf the Low of Conservqlion of Mqss. If soys lhqt, in q chemicol reqction, lhe fofql mqss of the reqclqnts equols the tofol mqss of the producfs. If 贸 gromsof hydrogenis combinedwith oxygento form 54 gromsof woter,how muchoxygenwos used? Youcon find the onswerby writingond solvingon equotion. Remember, when you solveon equotion,you ore f indingo numberthot will reploceo symbolond mokethe equotiontrue. Letx represent the numberof gromsof oxygen. gromso[ hydrogen

gromsof oxygen

gromsof woter

6+x=54 Theequotion 6 + x = 54 is trueonlyif thesymbolx is reploced by o certoinnumber. fry 45. Does贸 + 45 equol54? No. 45 is too smoll. Iry 48. Does贸 + 48 equol54? Yes. x= 48 Thenumber48 con reolocex to moke6 + x = 54 rrue. Theomouniof oxygenusedwos 48 groms.

Solveeochequotion.

,W"*2s=78

@tZS+n=贸00

t{p rez-x=e7 G} n*72s=Boo Write ond solveon equotionto f ind eochonswer.

to withchlorine ffi f ZOOg of sodiumis combined

give 508 g of sodiumchloride,how muchchlorine wos used?

to give40 9 of ffi ft SOOg of woteris decomposed

hydrogengos,.how muchoxygengos will be mode?

Findfive householdproductsthot ore chemicolcompounds. Exomples include toblesolt,bokingsodo,vinegor,bleoch, ond detergent.Reseorch to find the chemicolelements thot mokeup eoch compound.Forexomple,woteris mode up of hydrogenond oxygen.Moke o toble showingwhot you found.

Use Vocqbulory

i Exploin Concepfs I

chemicolchonge physicolchonge lp.3751 lp.375) polymer(p.3BB) chemicql equotion (p. 378) combustion !p.377)

producl (p. 3ZB) reoctonl (p. 378)

howrustforms. 8. Exploin 9. Controstphysicolchongeswith chemicol chonges.

lo. Exploinhow chemistsimprovednoturol rubberso thot it becomeo moreuseful moteriol.

Usethe termfrom the lisl obove thot best completeseoch sentence. l.

Ahoppenswhen one substonce chongesintoonothersubstonce.

thol is chongedin o chemicol A substonce reoctionis colledo -

formedfromsmoller A Iorgemolecule identicolunitsis colledo -

When objectschongeby teoring, or melting,but do notchonge crushing, hos ointodifferentsubstonces, occurreo.

The processof burningis colled

A substonce lhot formsdurinoo chemicol reoctionis colledo

A speciolsentencethol describeswhot 'hoooens in o chemicolreoctionis colledo

I l. â&#x201A;Źonclude With o cold sportspock,you twistthe pock, cousingtwo substonces to mix. Thesportspock quicklybecomes cool. Hos o chemicolreoctionoccurred? Exploin.

I2. Infer Referto the picluresof the flome teston pqge 385 ond reod the coptions. How do you know thot chloridegivesoff no strongcolor in thistest? 13. Model Moke o modelout of cloy to showhow otomscombineto formsodium chloride(NoCl).Moke onothercloy modelfor silvernitrote(AgNO3).Use both modelsto showwhol hoppenswhen sodiumchlorideond silvernitrotereoctin o replocemenlreoction. 't

Use Vocqbulory

i Exploin Concepts i

chemicol chonge (p.375)

physicol chonge (p.325)

chemicol equolion {p. 3ZB)

polymer (p. 3BB)

howrustforms. 8. Exploin

9. Controstphysicolchongeswith chemicol cnonges.

combustion lp. J/ /l

producf (p. 378) reoclqnl (p. 3ZB)

ro.Exploinhow chemislsimprovednoturol rubberso thot it becomeo moreuseful moteriol. )t

Usethe lerm from the list obove thot best completeseoch sentence. I. 2.

A_ hoppenswhen one substonce nce. chongesintoonothersubsto thot is chongedin o chemicol A substonce reoctionis colledo formedfÂĄomsmoller A lorgemolecule identicolunitsis colledo -. When objectschongeby teoring, or melting,but do notchonge crushing, hos into differentsubstonces,o occurred.

Theprocessof burningis colled A substonce thot formsduringo chemicol reoctionis colled o -. A speciolsentencethot describeswhot hoppensin o chemicolreoctionis colledo

I t . Conclude With o cold sportspock,you twist the pock,cousingtwo substonces to mix. Thesportspock quicklybecomes cool.Hoso chemicolreoctionoccurred? Exploin.

12.Infer

Referto the picturesof the f lome teston poge 385 ond reod the coplions. How do you know thot chloridegivesoff no strongcolorin thistest?

Ăş

: 1 3 . Model Moke o modelout of cloy to showhow olomscombinelo formsodium chloride{NoCl).Moke onothercloy modelfor silvernitrote(AgNO3).Use both modelsto show whot hoppenswhen sodiumchlorideond silvernilrotereoctin reoction. o replocement

{

8$ $sttindPoinf

W o"o* Conclusions 14. Reodthepossoge. Thendrow o conclusion bosedon thefocrs.

Mony moteriols hove beencreoted by chemists.Silk wos expensive,so chemistsworkedto moke o fobric to reploceit. Plosticsore inexpensive comporedwith metolsond other moteriolsthot plosticshove reploced. Moke o grophicorgonizerlikethisone. Putthe foctsond conclusioninto your grophicorgonizer. Foct

ffi-

Conclusion

Focl

ftrt"rf

Prep

Choosef he lelterthof bestcompletesthe stotemenlor onswersthe quesfion. 15. Which is on exompleof o chemicol chonge? @ woter f reezingin o puddle @ o dry spongeexpondingofter being put in dishwoter @ food being digestedin the smoll infesfine @ buttermeltingin o microwoveoven

| รณ. Whot kind of reoctionoccurswhen wofer breoksdown, producinghydrogenond oxygengoses? reoction @ o combinotion reoction @ o decomposition recombinof ion o reoction @ @ o replocementreoction | 7. Which molerioldid chemisls mokein the lob? @ cotlon @ wool @ silk @ nylon 18. If you ore goingto useo cleoningproduct you've neverusedbefore,whot should you do first? @ Open the window. @ Puton cover goggles. @ Reodthe direclions. O Puton gloves. | 9. Exploinwhy f he onsweryou chosefor QuestionI B is best.Foreoch of the onswersyou did not choose,give o reosonwhy if is not lhe bestchoice. . .rr. @!G : o tยกr* li*.howยกnq

rrqrrqflYr rYruKe four mointhinos

you've done so for todoy.Thenwrite o norrotivetellinghow eoch of these octionsinvolvedone or morechemicol reoctions or chemicoltechnologies.

399

If you ore olwoys wondering whot fhings ÂĄÂĄre mqde of, you moy enjoy q cqreer in mqferiqls science. yourjob would be to study As o moteriqlsscientist, of differentmoteriols. the otomicor moleculorstructure work moinlywith metols.Others Mony moteriolsscientists on olostics.Somework with semiconductorsconcentrote moteriolsimportontin computers. Stillotherscombineo voriety of moteriolsfor differentuses.

Theytesthowwell scientists designnewmoteriols. Moteriols theyfigure the moteriolswork in differentproducfs.Sometimes the moteriols. Moteriols out the bestwoys to monufocture scientists oftenwork in o lob. Theyneedgood mothond scienceskills.Theyusuollywork with o teom.Therefore, they needto be oble to communicote well foceJoJoce.Theyolso need io reportobouttheirwork, so they mustknow how to write well. Forthiscoreer,you will needo or degreein physics,chemistry, Evenofteryou hoveo job, engineering. you will needto continueyour educotion.

Thiswill helpyou keepleorningoboutthe newmoteriols thotore olwoysbeingproduced.

Identifydifferentmoteriolsin objects in ond oroundvour home.Moke o chort thot liststhe moteriolsond the tvpesof objectseoch is usedfor. In o third column, you listchemicolond physicolproperties think mokeeoch moteriolgood for its uses.

Explore Howconyou leornoboutthe motionof o pendulum? Whor lo Do

Moferiols

Mokeo pendulum. sofety goggres _

\'.

-,- i,. .: -''

-' wosherond stringt"-

ffir{"'

Pullbockthependulum 30 cm. Letgo. Observe how thespeed duringo swing. chonges Whene doesthe woshenrnovefostesf?slowesf? Whene doesif speedop?slow down?

moskingtope

Testogoin from 30 cm bock. T i m e5 s w i n g s .

ond meterstick

C -

mer or stopwotch

r-Youobserve

whenyou useyour senses lo gother informolion. Youinfur when you mokeo judgmenlbosed on observotions or exper¡ences. Youpredicl when you moKeon inference obouto fulureresult. You exploinwhenyou clorifythereosons is the something woy it is.

A "swing"is onebock-ond-fonfh rnovemenf.

Predicthow pullingbockthe pendulum ó0 cm wouldoffect thetimeneededfor 5 swings. Testyourprediction. Time5 swings.

;

Pollbockondleig.. <-m

Weonsofetg goggles.

Thedownwondpollof Eonfh'sgnovitgsfonts the pendulurn moving.

Exploin Your Results t. Comporethetimeneededfor,30cmondó0cm o pendulum swings.Infer howthedisionce swingsoffectsthetimeo swingtokes. 2. Predicr Supposethestringwos shortened. How do you thinkthiswouldoffectthetime o swingiokes?Exploin. loko lt to lht Not p€orso¡succossnel.@m

''@co,rre qnd Effect Understondingcquses qnd effects con help you understond whot you reod.A cousemoy hovemorethonone effect.An effectmoy hove morethonone couse. r Sometimes on effectwill be the couseof onothereffect. ยก Sometimes you hove to infer the couseor effectfrom the informotiongiven. Possogefrom o Sf,ory Sondy pushed Somuel on the swing. Eoch push mode Somuel go higher. Becouseof this, Somuel become ofroid. So, Sandy stopped pushing. Since he wosn't being pushed onymore, Somuel slowly come to o stoD. But he wos still ofroid.

Apply It! Moke grophicorgonizers likethe onesshown.Under Couses,write on ociion thot hoppenedin the story. UnderEffects.write whot hoppensos o resultof the couse.In thisstory,eoch effect becomeso couse for onothereffect.The grophicorgonizersore stortedfor vou.

Couses Sondypushed

Somuelwenl higher.

Effecls Somuelwent higher.

262 kilometers per hour. You left Son Diego this morning ot eleveno'clock, ond you'll be in Los Angelesbefore noon. Did you know o troin could move thot fost?

lesson I

How canyou motion? describe

Seosl,orsore onimols thot movevery slowly.

. Leaveswaveand dance in the wind. A ball bouncesback and forth from one child to another.A bird flies right, Ieft, up, and down. Youcan describemotion in manv wavs.

Types of Motion You spend every moment of eoch doy moving in one woy or onother. You wolk down hollwoys ond stond

up from choirs. At night you roll over in bed. Your heort beotsond your eyelidsblink up ond down. Motion is oll oround you. Objects move in mony different

woys. Whot kinds of motion hove you seenin your clossroom? Different kinds of motions con hoppen ot different rotes. A seo stor moves so slowly thot sometimes you con hordly

tell whether it is moving. Other obiects,such os on oirplone's 11 ropeller,move so quickly you needo high-speedcomero ;. to cotch sight of them. Think obout the different kinds of motion. The ;. Eorth hos o steody, or constant,motion os it moves

oround the Sun. Cors,trucks,ond buseshove 'icble motion-they

move in mony directions

end ot mony speeds.A pendulum has periodic otion-it

swings bock ond forth. Wheels

move in a circularmotion. A rubber bond hos vibrationalmotion when you pluck it. How d you demonstrote eoch of these motions? I

ú9¡Cgl.eqint.t Whot ore threelypesof molion?

2 E@Ñ&@DescriptiveWriteo porogrophin your sciencejourncl describing lhe motionsyou hoveenjoyedon ployground equipmenl.Write your porogrophin the styleof o mogozineorlicle.Usethe heodline"TheBestRide on the Ployground."

Speed ond Velocity I

Averogespeeddescribeshow for on obiectmovesduring o certoin omount of time. To colculoteoverogespeed,usethe following formulo: AverogeSpeed-

Distonce Time

If o cor moved 1O0meters in 20 seconds,its overoge speed would be:

100m

20s

-57

When you sit os still os you con, ore you moving? Do not be too quick to soy^youore not moving. In relotionship with your choi4,you moy be sitting still. In relotionshipwith the Sun,you ore moving very quickly. You ond the planet you ore sitting on ore moving around the Sun fosterthon ony rocket.So,the motion of on obiectconnot be meosuredby iust looking ot the oblect.Motion is olwoys meosuredin relotionship with some locotion colled o point of reference. The speedot which a personis moving con vory occordingto which point of referenceyou use.For exomple, o possengerwolking down the oisleof o troin is in motion. But the possenger's motion meosuredin relotionship with the end of the troin cor is different thon the possenger's motion relotive to o crossinggote olong the trocks.

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Using the end of the troin cor os o point of reference,the possengerwolking 10 metersdown the oisle in 5 seconds will hove o wolking speedof 2 metersper second.But using the crossinggote neor the trocks os o point of reference,the possengeris moving obout os fost os the troin-perhops 30 metersper second.

l o m - ' s^ m 5s

-- w !!-Q..1tr en[ "s

SignolLight Y

Speedond velocity ore not the some.Veloci$ describesthe speedond the direction of on obiect'smotion. The speedof the troin might be describedos 30 metersper second,but its velocity is 3Ometersper secondnorth. A folling skydivermight hove o velocity of obout 200 kilometersper hour down.

ยก! tesson Checkpoint, l. Robertmoved28 metersin 4 seconds.Tollonomovedรณ00 meters in 2 minutes.Joviermoved40 melersin 5 seconds.Lislfhese peopleond their speedsin order from foslestto slowesl.

2. Whot do you needto know to find on object'svelocily?

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in your ExposiroryWrite o porogroph

sciencejournol thotexploinshowcirculormotionond vorioble motionoreolikeonddifferenl.

Thishoin is movingot o hยกghspeedfrom the pointof reference of the crossinggofe.

lesson 2

What areforces? Thereare many kindsof pushesand pullsaroundyou. An opplefollsto the groundbecouse the Thesepushesand pullscan causeobjectsto changetheir forceof grovitypulls velocities. it 端owqrdEorth'scenler.

Pushesond Pulls

Gro端tycousesfhe velocityof theopple lo increose os it folls.

A force is o push or pull thot octs on on obiect. When one obiect pushes or pulls onother oblect, the first obiect is exerting o force on the second one. Forcescon moke o moving obiect speed up, slow down, or chonge direction. Forceshove both mognitude ond direction. The mognitude of o force is how strong the force is. Mognitude is meqsured in units colled newtons (N). The direction of o force con be describedby telling which woy the force is octing. For exomple, o medium-sized opple held in your outstreched hond exerts o downword force with o mognitude of obout 1 newton.

Grovity

After one secondof folling,on opple's velocitywill be obout l0 S downword.

After two secondsof folling,on opple's velocitywill be obout 20 f downword.

410

Everyobiectin the universeexertso grovitotionol pull on everyother obiect.But only the grovity of o lorge obiectsuch os Eorth is strong enough to be felt. Eorth's grovity pulls other obiectstoword its centerwithout evertouching them. Pendulumsswing, opplesfoll, ond ortiflciol sotellitesstoy in orbit becouseof Eorth'sgrovity. An obiect'sweight is the omount of grovitotionoforcebetweenit ond Eorth. This forcedependson the object'smossond Eorth'smoss.It olso dependson Eorth'ssizeond how for gbove Eorth the obiectis. If you fly in on oirliner, your weight is o little less.If ypu went to onother plonet, your weight would olso chonge. The toble on the next poge shows how much on object would weigh on some other plonets if its weight on Eorth is 100 newtons.

t Z

thot fTCnectpoint.Whot orelwo exomples illustrote Eorfh'sgrovitotionol pull?

down O C<ยกuseond EffecrA rocktumbles o hill.Identifythe couseond effectof thisevent.

Mognefism ond Electricity Mognetism is o force thot pushes ond pulls on other obiects. The mognetic force is greotest ot o mognet's poles. The poles ofo horseshoemognet ore ot the two ends. The poles ofo bor mognet ore ot either end. Every mognet hos o north p.oleond o south pole. Mognets will strongly pull on objects mode of iron, cobolt, nickel, ond godotrinium. Mognets will olso exert forces on other mognets. The north pole of one mognet will ottroct the south pole of onother mognet. The north poles of two mognets will push owoy from eoch other. The south poles of two mognets will oct in the some woy. Electric forces oct between obiects thot ore A mognel exerts electricolly chorged. Obiects get electricolly chorged mogneticforcethot when they goin or lose electrons. Remember thot pullspiecesof iron oll otoms hove negotive electrons ond positive toword it. protons. If on obiect goins electrons, the obiect will be negotively chorged. If the oblect loses electrons, A negotivelychorged it will be positively chorged. Why would on object combwill ottroct poperbecouse of get o positive chorge if it loses electrons? eleciricolforces. Electrons often move from one obiect to onother when the obiects ore rubbed together. When silk ond gloss ore rubbed together, electrons will move from the gloss to the silk. The rubber comb con goin o negotive chorge from your hoir. AII objects thot ore electricolly chorged will exert forces on eoch other. Oppositely chorged objects ore ottrocted to eoch other. Obiects with the some chorge ore repelled, ond moy .move owoy from eoch other.

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Grovity, Electricity,ond Mognetism Like grovity, mognetic qnd electric forces con oct between objects even if the obiects do not touch. All three forces increose os obiects get closer together. Grovity, electricity, ond mognetism hove differences. The forces of mognetism ond electricity behveen obiects con be blocked by putting certqin kinds of moteriols between the obiects. Grovity con't be blocked. Electricity ond mognetism con push or pull on different oblects. Grovity exerts only o pulling force on obiects. Mognelicforcescousethis experimen端ol troin lo floqt obovethetrock.Mognetic forcesore olsousedlo mokethe Foin moveolong thetrockot very high speeds.

t&Cnecfpoint. Whol ore the cousesof electric ond mogneticforces? '@ 2. Cause ond Effect Describeon event involvingeleclricond mogneticforces.Useyour imoginotion.Describethe couseond effectof eoch force.

Themogneticfieldof this stoneotlroctsmetolpins lo itssuloce.

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Friction

Theshopeof shorks ond theirspeciolskin reducefrictionwith he woler ond ollow theshorksto swim smoothlyond swiftly.

Speciolpodson o bicycle'sbrokespush ogoinstthetires.fhis resultsin increosed frictionthot slowsdown or stopsthe bicycle.

414

Hove you ever slid ocross o smooth floor with your sockson? You con't slide os eosily if you ore weoring your shoes.Friction is ot work. Friction is the force thot results when two moteriols rub ogoinst eoch other. Friction octs to slow down the motion of on object or keep it from storting to move. Unlike other forces, friction depends on quolities of the objects involved. The shope, speed,or texture of one object con offect the omount of friction with onother obiect. The texture of the soles of your shoes is different from the texture of your socks. Friction is greoter between your shoes ond the floor thon beftveen your socksond the floor.

A bicyclehosmonyfeotures thot increosefriction.Other fuotures,like boll beorings, decreose friction.Both mokethe bikesofer ond eosierio ride.

Air ond woter resist motion when o moving obiect pushes ogoinst them. Air friction is o force thot is present when oir flows over o surfoce. Flowing woter hos o similor kind of force. Most cors ond oirplanes ore designed to hove little oir friction. Submorines ond ships ore designed with shopes to help them move through woter.

1. J, 2.

. How doesf rictionoffect movement?

Theorovitotionolforce on the Moon is one-sixthof whot it is on Eorfh.Thismeonsthot on the Moon you would weigh one-sixthof whot you weigh on Eorth.How muchwould you weigh on f he Moon?

Thedistonceit tokes 端ostopo skiddingcor dependson lhe surfoceof the rood.

100

150

StoppingDisto単ce{ml lrom 45 km per h

On somebicyclesthe ollow : low hondlebors 'the riderto benddown ond decreose oir friction.

Thetextureof thefoomon the hondleborincreoses frictionbetweenthe rider's hondsond the hondlebors, mokingit eosierio hoveo firmgrip.

Theroughtreod on thisbicycletire increoses thefriciion betweenthe tire ond theground.This keepsthe bicycle from slidingduring lurns.

4L5

Work qnd Power You heor the word "work" usedoll the time. But the scientificdefinition of work hos o porticulor meoning. I/Vork is done when o forcemoveson object.To colculotework, you multiply the force (in newtons)octing on on obiectby the distoncethe forcecousesthe obiectto move. Force x Distonce: Work

Work is meosuredin joules. One ioule (f) is the omount of work done when o force of 1 newton (N) moveson obiecto distonceof 1 meter (m).

If the force opplied to on object does not moke the obiect move, then no work hos been done. Work is done only when the obiect moves ot Ieost portly in the some direction in which the force is opplied. Holding on object in ploce con require o force, but since the obiect does not move, no work is done. Force

10N

Disfronce

Work l0Nx0m:0J

Work is done wheno force moveson object.

Power is the rote ot which work is done. When work is done faster, power is increased. Wolking up o hill ond running up the some hill toke the some omount of work. Since running up the hill is foster thon wolking, the omount of power needed to run is greoter. You con colculote the omount of power for o certoin omount of work. Divide the omount of work done by the omount of time needed to do the work. Wotts ore the units of oower.

Work -

Power

Time

The toble below shows thot the omount of power will double if o person doubles the omount of work done during o certoin omount of time. Power will olso double if o person does the some omount of work in holf the time.

Work

Time

20J

/l-

40J

20J

Power

H:,* fl:

row

20J _ t0w 2s

No work is beingdone whenon objectis held withoutmoving,no motier how longtheobjectis held.

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t . Whof ore two exomplesof forces? ')

3. t

Whol kind of force con mokepoperclinglo o comb?

thotshowhow Findpicfures the shopesof cors hovechongedover time.Describe feotureson moderncorsthof help reduceoir friction.

4t7

lesson 3

What areNewton's lawsof motion? A ball rolls fasterand faster as it travelsdown a hill. Finally it bumps into a tree and stops. Newton'slaws of motion explaĂn why objects Iike the ball move the way they do.

Net Forces Different forces con oct on on obiect ot the some time. They moy oct in different directions, ond some moy be stronger thon others. The combinotion of oll these forces is the net force on the obiect. The net force determines whether the obiect will

stort moving, stop moving, or chonoe direction.

If o stondingbox is pushed in onedirectionby more lhononeforce,the netforce is lhe sumof theforces.

418

An oirplonemovesin o stroightline ot o constront speed.It speedsup, slowsdown, or chongesdirectiondependingon e net forcesoctingon it.

Drogis o forcethot pushesogoinstthe forword mofionof on oirplone,slowingit

When equol forces oct on on obiect in opposite direc端ons, the forces ore bolonced. Then the net force is zero. Bolonced forces do not chonge the woy on obiect moves. An obiect is in o stote of equilibrium when oll the forces octing on it bolonce eoch other. A stonding oblect in equilibrium will remoin motionless. A moving obiect in equilibrium will continue to move ot o constont speed in o stroight line. If the forces octing in one direction ore greoter thon the others, the forces ore unbolonced. Unbolonced forces octing on on obiect couse it to chonge its motion. The net force is found by combining oll the different forces octing on on obiect. For exomple, if two people ore pushing on o Iorge box from opposite directions using the some omount of force, the box does not move. But if one person pushes horder thon the other, o net force results ond the box moves. I

How con on objectbe mofionless ond Sg!fe,.l1pgig_.,; in eouilibrium? 2. @Couse cnd Effect Howcon theforcesin o gomeof lugof-worresultin equilibrium?

Thrustpushes on oirploneforword, mokingit occelerole.

zero N

If o siondingboxis pushedin opposite directions by equol forces,theforcesore bolonced. Thereis no nelforce,ondlhe boxdoesnol move.

If o box is pushedin opposiiedirections by unequolforces, theforcesore unbolonced. There is o netforcein thedirectionof the stronger force,ond lhe box movesin thotdirection.

4L9

Nerrlon's First Lqw Newton's first lqw of motion soys thot unless o net force octs on on object, the obiect will remoin in constont motion. An obiect ot rest stoys ot rest until o net force octs on it. An obiect moving ot o constont speed will continue to move in o stroight line ond ot o constont speed. The tendenry of on obiect to resist ony chonge in motion is known os inertio. Objects with o lot of moss hove more inertio thon obiects with Iessmoss. The body's inertio is whot forces you ogoinst the side of o cor when it turns. When o cor chonges direction, your body tends to keep moving stroight. The cor is pushing on you during o turn. Inertio is olso whot mokes your body rise up from your seot in o roller cooster os it goes up ond over o steep hill. At the top of the hill, your body tends to continue going up when the ride moves down the hill. Spoceprobes ore olso exomples of Newton's first low ond inertio. Inertio keeps the probes moving through spoce. As o result, probes need very little fueI ofter they ore lounched. They usuolly use fuel only to chonqe direction or to slow down.

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Inertiohosollowedthe spoceprobe Voyogerto troveloll the woy out of thesolorsystemwhile usingverylittlefuel.

420

Alhough theforceof the kick is oppliedfor onlyo shorl time,ineriiowill cousethe footbollto continueto move throughthe oir ofter*re kick.

A full truckhos moreinertiothon on emptyhuck, ond it will toke moreeffort to mqkeit either speedup or stop.

A seotbeltpreventsthe testdummy'sinerlio fromcorryingthedummy throughthewindshield.

Whot is inertio?How doesit offect -y'7Gheckpoint.. the wov on obiect moves? Usephotogrophsfrom mogozinesto creoteo collogeobout Newfon'sfirstlow of motion. Try to find os mony exomplesos possiblethot illustrole thinqsthotore in constont motionor ot constont rest.

421

Nevvlon's Second Lqw Newton's second low of motion describeshow occelerotion, moss, ond net force ore reloted. Accelerotion is the rote ot which the velocity of on object chongesover time. The net forces octing on on object con chonge on obiect's velocity by cousing it to speed up, slow down, or chonge direction. All ofthese chongescon be colled occelerotions. The formulo thot describesthe relotionship between force. moss. ond occelerotion is:

Force= Mossx Accelerotion The formulo is often written os F : m x o. It indlcotesthot the strongerthe force octing on on object,the more thot obiectwill occelerote. The formulo olso indicotes thot o force wili couse on obiect with smoll moss to occelerote more thon on object with lorge moss. The occelerotion due to o smoll force on o smoll obiect con be the some os the occelerotion of o big force on o big obiect.

Thenetforceocting on the box is equol to the mossof the box multipliedby its occelerotion.

Force

Moss

200 N

100ks

Accelerotion .m Âż;Ă

Thetroinenginesmuslexeri enoughforceio pull the freightcorsbehindthem. Themorefreightcorsthere ore, the moreforcethe enginesmustexeri.

Newton's Third Low

Thepersonpusheson the woll. Thewoll pusheson the person.Forcesof the woll ond personore equol ond opposite.

Whenthe morbles collide,theywill exert forceson eochother.

Newton's third low of motion states thot when one obiect exerts o force on o second obiect, the second object exerts o force on the flrst object. This is sometimes colled the oction-reoction low of motion. Action-reoction forces ore olwoys equol ond opposite,ond they alwoys occur in poirs. This low con be seen oll oround us. Whenever you see on obiect move becouse of o force, there is on equol ond opposite force. It is actuolly impossible to hove one force without on equol ond opposite force! For exomple, o person who leons ogoinst o woll exerts o force on the wall. The woll exerts on equol force on the person in the opposite direction. If you hove ever ridden bumper cors, you know thot when o moving cor collides with o stopped cor, both drivers feel the force of the collision. The driver of the stopped cor feels o force ond storts to move. The driver of the moving cor feels on opposite force thot slows the moving cor.

Thered morbleexerts o forceon the blue morble.Thiscousesfhe bluemorbletrochonge itsvelocity.

Thebluemorbleexerls on equolbutopposile forceon the red morble.Thiscouses the red morbleio olso chongeitsvelocity,

Bothmorbles chongevelocity becouse of lhe forces.

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Althoughtheforceof the kick is oppliedfor onlyo short time,inertiowill cousethe footboll¡o continuelo move throughtheoir o{terthe kick.

A full truckhos moreinertiofhon on emptytruck, ond it will toke moreeffort lo mokeit eiñer speedup or slop.

A seotbeltpreventsthe testdumm/s inertio from corryingthedummy throughthewindshield.

Checkpoint-. Whol is inertio?How doesit offect ,y'7 the woy on object moves?

2. UMGG}

usephotogrophs frommogozines to

creoteo collogeoboutNewton'sfirstlow of motion. Try to f¡ndos monyexomples thol illustrote os possible thingsthotore in consfont motionor of constont rest.

42L

NeurJon's Second Lqw Newton's second low of motion describeshow qccelerotion, moss, ond net force ore reloted. Accelerotion is the rote ot which the velocity of on obiect chonges over time. The net forces octing on on object con chonge on object's velocity by cousing it to speed up, slow down, or chonge direction. All ofthese chongescon be colled occelerotions. The formulo thot describesthe relotionship between force. moss, ond occelerotion is:

Force: Mossx Accelerotion The formulo is often written os F : m x o. It indicotesthot the strongerthe forceocting on on obiect,the more thot objectwill occelerote. The formulo olso indicotes thot o force will couse on object with smoll moss to occeleยกote more thon on object with Iorge moss. The occelerotion due to o smoll force on o smoll obiect con be the some os the occelerotion of o big force on o big object.

Thetroin enginesmustexert enoughforceto pull the freightcorsbehindthem. Themorefreightcorsthere ore, the moreforcethe enginesmustexeri.

Thenetforceocting on the box is equol trothe mossof ihe box multipliedby its occelerqtion.

r Force

Mqss

200 N

1 0 0k s

Accelerotion

Thereore different ways to write the formulo for the secondlow of motion. The formulo you usedependson whot questionyou ore trying to onswer.If you want to find the occelerotionof on objectthot hos o forceon it, you con usethe following formulo.

F m

To slowdown morequickly, o rocecor needsio hoveo big force.With o porochute, theforceof qir frictionis increosed ond thecor slows down morequickly.

If you wont to find the moss of on object thot hos o force on it, vou con use the formulo below. m=;.

.!0Cnec*point;UseNewton'ssecondlow of motionfo exploinwhot hoppenswhen someonepusheso choir ocrossthe floor.

Whot formulo wouldyou uselo find theoccelerotion of o l0 kg boulderbeingpushedby o forceof 贸5 N? Whot wouldthe occelerotion be? The.greobr the net forcepushingon the bo:q fhe greoler theoccelerotion of the box.

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Thegreotrer lhe moss of o box, the lessthe occelerotion will be.

Force

Mqss

400 N

200ks

Accelerotion ^m

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423

Newlon's Third Low

Thepersonpusheson the woll. Thewoll pusheson lhe person.Forcesof the woll ond personore equol ond opposite.

Whenthe morbles collide,theywill exerr forceson eochother.

424

Newton's third low of motion stotes thot when one obiect exerts o force on o second object, the second obiect exerts o force on the first obiect. This is sometimes colled the oction-reoction low of motion. Action-reoction forces ore olwoys equol ond opposite,ond they olwoys occur in poirs. This low con be seen oll oround us. Whenever you see on object move becouse of o force, there is on equol ond opposite force. It is octuolly impossible to hove one force without on equol ond opposite forcer For exomple, o person who leons ogoinst o woll exerts o force on the woll. Ihe woll exerts on equol force on the person in the opposite direction. If you hove ever ridden bumper cars, you know thot when o moving cor collides with o stopped cor, both drivers feel the force of the collision. Ihe driver of the stopped cor feels o force ond storts to move. The driver of the moving cor feels on opposite force thot slowsthe movino cor.

Thered morbleexerts o forceon the blue morble.Thiscouseslhe bluemorbleto chonge itsvelocity.

Thebluemorbleexerts on equolbut opposite forceon the red morble.Thiscouses Ăşe red morbletroolso chongeifsvelocity.

Bothmorbles chongevelocity becouse of the forces,

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l. Wh¡chof Newton'slowsof motionis demonstroted by o hommerpounding o noil intoo boord? 2. A sotelliteorbitingEorthis knockedout of orbit by o meteor.How con Newton'slows of motionbe used¡n describingthisevent? '@ 3. Couse ond Effect Whot w¡ll be the effectof two peoplepulling on o box wilh lhe someomountof force buf in oooositedirections?

Lesson 4

What aresimple machines? Simplemachinesmakeworkeasier.Everytimeyou use a hammer,a screwdriver, or a doorknob,or walkup a ramp,you areusinga simplemachineto do work.

Mqchines ond Work Remember thot work is done when o force couseson obiect to move. Some obiects ore lorge, heovy, or owkword to move. A mqchine is o device thot chonges the direction or the omount of force needed to do work. Simple mochines ore mochines with only o few ports. There ore severol kinds of simple mochines, including o wheel ond oxle, pulley, inclined plone, ond lever. Mochines do not reduce the omount of work thot needs to be done. They con moke it eosier to do the work. When o mochine ollows you to use o smoller force to do work, you must opply thot force for o greoter distqnce. In this woy, the totol omount of work stoys the some.

Pulley A pulley is one type of simple mochine. A pulley consistsof o rope or coblethot runs through o giooved wheel.A simple pulley mokeswork eosier by chongingthe directionof the forceneededto do work. Flagpolesond dropery rods usepulleys. A block ond tockle is o systemof pulleys thot moke it eosierto lift very heovy oblects.

Thispulleydoesnot chongelhe omountof work done.fhe mossof the box pullsdownon the pulleywith o forceof l0 newlrons. Theperson mustpull on the pulley ropewi$ fie someforce. Noticethot if the ropeon thispulleyis pulleddown I mefrer,the box is lifted up I mel,er,

426

Lesson4

What aresimple machines? Simplemachinesmakeworkeasier.Everytimeyou use a hammer,a screwdriver, or a doorknob,or walkup a ramp,you are usinga simplemachineto do work.

Mqchinesond Work Remember thot work is done when a force couseson obiect to move. Some obiects ore lorge, heovy, or owkword to move. A mochine is o device thot changes the direction or the omount of force needed to do work. Simple mochines ore mochines with only o few ports. There ore severol kinds of simple machines, including o wheel ond oxle, pulley, inclined plone, ond lever. Mochines do not reduce the omount of work

thot needsto be done. They con moke it eosier to do the work. When o mochine ollows you to useo smoller forceto do work, you must opply thot forcefor o greoterdistonce.In this woy, the totol qmount of work stoysthe some.

Pulley A pulley is one type of simple mochine. A pulley consistsof o rope or coblethot runs through o giooved wheel. A simple pulley mokeswork eosier by chongingthe directionofthe forceneededto do work. Flogpolesond dropery rods usepulleys. A block ond tockle is o systemof pulleys thot moke it eosierto lift very heovy oblects.

Thispulleydoesnot chongetheomounlof work done.fhe mossof the box pullsdownon the pulleywiih o forceof l0 newlrons, Theperson mustpull on the pulley ropewith thesomeforce. Noticethoi if the ropeon thispulleyis pulleddown I mefer,the box is lifted up I meler.

426

Wheel ond Axle A wheel ond oxle is mode up of o circulor obiect, such os o doorknob, ond o shoft. A wheel ond oxle mokes work eosier by reducing the omount of force needed to do work. Imogine how hord it would be to lift o bucket out of o well by iust pulling it stroight up! Using o wheel ond oxle for tosks like roising o bucket in o well chonges the direction of force from circulor to o stroight line. The steering wheel of o cor is onother exomple of o wheel ond oxle. I . JCnec*point, Whot oretwo exomples of o wheel ond oxlethotcon mokeworkeosier?

2 E!EÑE@@ ;l¡t! I

Usethelnternetoro

libroryto find theeorlieslrecordedusesof simple in yourscience mochines. Write I or 2 porogrophs journcl on yourfindings.

Bollbeoringsore steel bollsusedinsideo wheelto reducefriction ond mokeo pulleyor wheelond oxlemore efficient.Thebeorings ore greosedto help themfurn moreeosily.

Thepulleyshownfr heremokes W.

workeosier.less ?1 forceneedsio be fr 7ú1 ^ oppfiedovero longerdisüonce. Only 5 newtons will be neededto lift the lO-newfon box. Noticeúot if the ropeon úis pulleyis pulled I meler,the box is liftedonly 0.5 meler.

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on thewell is o kindof wheelond oxlethot reducesthe force neededio roiselhe bucketYourhondsopply o forcefor 90 cmwhile roisingthebuckeionly l0 cm.Youore opplying lessforcelhonyou would if you liftedsroighi up on the rope.Butyou opply fie forceover o greolrer. distonce.

..| .;

Lever A lever is o type of simple mochine in which o stiff bor rototes oround o fixed point colled o fulcrum. Levers do work by using the stiff bor, the fulcrum, o lood, ond o force you opply. A lever such os o see-sowchonges the direction of o foice. When o person useso see-sowto lift o box, the person pushes down, but the box goes up. As the position of the fulcrum chonges, the omount of force needed to move the box will chonge. The forther the fulcrum is from the person using the lever, the eosier the lever is to use. Above ond to the right is o picture of o person lifting o box with o lever. The force thot the person must opply is lessthon the weight of the box. This mokes the work eqsier.Also notice thot olthough the needed force is less,the person must opply this force for 1 m while the box goesup only 0.5 m.

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A leverchongesthe directionof o force.

Other Simple Levers

Monyeverydoyitems hove levers.How do the portsof theseitems helppeopledo work?

Lever A lever is o type of simple mochine in which o stiff bor rototes oround o fixed point colled o fulcrum. Levers do work by using the stiff bor, the fulcrum, o lood, ond o force you opply. A lever such os o see-sowchonges the direction of o foice. When q person useso see-sowto lift o box, the person pushesdown, but the box goesup. As the position of the fulcrum chonges, the omount of force needed to move the box will chonge. The forther the fulcrum is from the person using the Iever, the eosier the lever is to use. Above ond to the right is o picture of o person lifting o box with o lever. The force thot the person must opply is lessthon the weight of the box. This mokes the work eosier.Also notice thot olthough the needed force is less,the person must opply this force for 1 m while the box goesup only 0.5 m.

I ;rl '..

A leverchongesihe directionof o force.

Orher Simple Levers

Monyeverydoyitems hove levers.How do the portsof theseitems helppeopledo work?

Inclined Plones Hove you ever tried corrying o heovy lood up o flight of stoirs?It's much eosierto roll it up o romp! An inclined plone is onother type of simple mochine. It consists of o flot surfoce with one end higher thon the other. The inclined plone con be o romp lorge enough for o person or o vehicle to use, or it con be very smoll. Thedistoncefrom the floor stroightup to the plotformis lessthonfie dislonce usedwith the inclinedplone.Butmore forcemustbe oppliedio lifi the box directlyfrom thefloor onlo the plotform.

If you pusho wheelchoirup o romp,you woulduselessforce overo longerdistoncethonif you wereto lift thewheelchoir to thesomeheight.

Other Inclined Plones

A screwis o smoofi melol rod with o tiny inclined plonewroppedoround it. Screwscon be usedto pull two piecesof wood togetherond holdthemin ploce,Screwsconolsobe usedin jocks thot lift cors.

Pushingo box up on inclinedplonef,oo plotformis mucheosierihon liftingfie box. Usingtheinclined plonecoversmoredisionce,but o smolleromount of forceis used.

t. 2.

Whot ore the portsof o lever? Mony joints in your body work likesimplemochines. Yourkneeond elbowjointsore likelevers.Thinkof two octivities ยกn whichthe kneesor elbowsoct os leversto do work. Where is lhe fulcrumin eochoctivitv?

A rubberdoorstopis o smollwedgethotis usedto keepo doorfrommoving. Thisdoorstrop is o wedge thotconsists of oneinclined ploneond oneflot plone, Somewedges,suchos on oxe, ore modeof two inclinedplonesplocedbock o to bock.Thiscreotres thot be mochine con used to splitwood.

429

Complex Mochines A mochine thot usestwo or more simple mochines is colled o complex mochine. Mony complex mochines use electricity, grovity, burning fuel, humon force, or mognetism to operote eoch of the simple mochines within it. This go cort is on exomple of o complex mochine.

Thiscroneis o complexmochine. Whot simple mochines conyou seein lhe crone?

Thesieeringwheel is port of o wheel ond oxle thot mokes it eosiertroturnthe 90 corl.

wheel

axle

Thewheelond oxle of the steering wheel movelevers thot turn the front wheel.

Thepedolsore levers.Thedriver's

or brokes.

430

Soiling ships ore complex mochines. They hove mony ports thot work together to moke the ship move properly. Pulleys ore used to lift the soils into ploce. The rudder is o lever. A wheel ond oxle moy be used to move the rudder. A wheel ond oxle moy olso be used to lift the heovy onchor. Some soiling ships used oors to help move the ship. Oors ore levers. By.itself,ihe engineof lhe go cort is o complex mochinemodeup of monysimplemochines.

Brokesconioinlevers. Oneendof thelever is pulledby o coble, cousingtheoiherend to pressogoinsto disk thot is ottochedto the wheel.

ore complex Soilboots mochines fiot iurn wind energyinlrokineticenergy.

Theengineis not connecbddirecdy troĂşe tires.The georsore o systemof wheels ond oxles.

.S tesson Checkpoint, I . Why is o screwconsideredo simplemochine? 2. Nomeone complexmochineond two of thesimplemochines thot mokeit uo. 3. @ Couse ond Effect When you useo screwdriverlo open the lid of o pointcon, lhe couseis the forceyou opply to the screwdriverond the effecfis the lid comingoff. Describe the couseond effectof usingsomeothersimplemochine.

43L

Investigqte How con you describemotion? When soccerployerskick o boll, they esl¡mqte how it will move. invesligofemotionthey meosure. In thisoctivify When scientists you find how the speedond directionof o boll chongeos it moves olong,hitso woll, ond bounces off ot on ongle. Mqteriqls

Whor to Do

ffi,

moskingtope ** . at* ¡¡

"!, t:

@-P:;+i r*_fjfla\ .: :,: r 1-,:i "rl

prolrocror

Mork on impoctspotwith tope ot the bose of o woll. Puto protroclorot the impoct spot.At on ongleó0' out fromthe woll, meqsure o poth4 meterslong ond mork it with tope.At the poth'souterend, write SiortingLine.

' ,ij"'"-

"'-..

meterstick")

A t o n o n g l el 2 0 o o u t f r o mt h ew o l l , meosureo poth4 meterslongond morkit with tope.At the poth'souterend wrile EndíngLine.

timeror stopwolch

meo'ure us¡ng stondordunifs, suchos meters,or nonstondordunits suchos lhe length of o poperclip.

'l Fromobout meierbehindthe Storting line, gentlypushthe boll so it rollsolong the poth.Stortthe timerwhen the boll possesfhe SÍorÍingline (Time1)..Record the timethe boll hitsthe impoctspot (Time2). Stopihe timerwhen the boll crossesthe EndingLine(Time3).

thebolltrovelsondthetimeit tokes. @ Orophthedistonce

ImpocfSpof Recondthe tine.

Designondconsfn¿lcfo dofo loble ondo gnoph. Yooconselecifhe onesshownondesigngoonown. A foble ondgnophwillhelpgooongonize, displog. onolgze, ondexploingoondofo ondgortnfindings. I -4

EB,' r u , ¡ .ó ^

''-'':-,i I

. , , , - , - - - . : . . , .i . . .

I i

'r'

. I É iÉ: t; rtll .E,E; : d"*'í"-'f "'.3---?*-í-*¿"*'7" " s' ll

:ll,

Time (seconds)

Yoonfeochennighf oskgoufo ctsegnophpopen.

Exploin Your Results l . Usingyour meqsuremenfs, find the boll's speedfrom the StortingLineto the Impoct Spot.Findthe speedfrom the ImpoctSpot to the EndingLine. speed=disfonce+firne

2. Infer Did the boll moveot o steodyspeed?

Howwouldyourgroph be differentif youshowed yourresuhs in feetinsteod of meters? Findout.Writeo reportof yourresults in your journol. science

Exploin youronswer.

433

You hqve leqrned thqf fhe mqss of ony moller is fhe sqme on fhe Eorfh or in spoce. Weight, however, depends on fhe force of grovity. Thegrovitotionol forceon theMoon is i of thegrovitotionol forceon Eorth. 'l How muchwouldo 8O-oound ostronout weighon theMoon?

jxtBO=#=so An ostronoutwho weighs180 pounds on Eorthwould weigh only 30 poundson the Moon. You hove leorned thot power describes how fqst work is done. How muchpower is neededto complete 150 joulesof work in 40 seconds? power is meosuredin wotts. Remember, ^ = work lOWe[

-. flme = r50 ,lo

= 39 or 3.25 The oower neededis

or 3.25 wotts.

Answereochouestion. 'l . An Apolloostronout's life support systemwos o bockpockthot hod o totolweightof obout贸8 poundson Eorth.About how monypoundsdid the bockpockweigh on the Moon? 2. How monyjoulesof work ore done when o force of 2 newronsmoves on object2.5 meters? Remember, Work = force x distonce. 3. How muchoower is needed to complete210 joulesof work in 贸0 seconds?

Usethe librorv or the Internetto find more informolionoboul the Eorthweight of items the Apollo ostronoutswore or corriedwhen they wolked on the Moon. Findthe weight of eoch itemon the Moon.

Use Vocqbulory

i Exploin Concepts

occelerolion lp.4221

mochine$. a26l power (p.417)

equilibrium {r];i¡

velocitY(P aoe)

ro.Exploin howyouconuseo simple

force(p.410)

work (P'4]ó)

Exploin why on objectin o stoteof equilibrium couldbe eitherin motion or stonding still. mochine lo mokeo job eosier.

inertio (p.420) Uselhe vocobuloryword f rom the lisl obove thot bestcompleleseoch sentence. I.

An object resistso chongein molion becouseof

Ais o devicelhot moresworr eosierto do.

Theof o movingobject describes its speedond direction.

When oll forcesoctingon on object bolonceeoch other,lhe object is soid to be in o stoleof

Grovilyis o thotpullsobjects towordthecenlerof fhe Eorth. is done when o force moveson object. rs TneroTeoTwntcn vetoctry

is the rote ot which work is done.

436 @,ü'!!{s"tg&

I t . Predict whot would hoppento o rofl f loofing on o loke if o swimmerdivesinto the woter from one end of the roft.

12. Observe

Comporeond controslo pulley ond o wheelond oxle.

Cquseqnd Effect

| 3. Moke o grophicorgonizerlike fhe one shownbelow.Underthe word Effecl,use Newton'ssecondlow of motionto exoloin whot will hoppen. !,

Effect

€ouse One ice skoter is skofing forword. A secondskoter comesfrom behindond gent¡ypushes the firsl skoter.

Rt"rt

Prep

Choosethe letterthot bestcompletesthe slolementor onswersthe question.

| 4. Sotellitesore held in orbit oroundEo¡h becouseof @ the Sun'sgroyity. @ thrustfrom the sotellite. @ Eofh's grovity. @ drog f rom the sotellite. | 5. Which of the followingstotements is f rue obout horseshoemognets? @ The mogneticforce is strongestin the middleof the mognel. @ The mogneticforce is weokestot the lwo ends. @ Thereis one pole ot the middleof the mogner. @ The mogneticforce is strongestot the two poles. | ó. Colculotef he power in wolts usedif you exert50 joulesof work in 5 seconds.

@ 2s0w @ low o 55W @ 45W

| 7. Keishotokeson hourto ride her bicycle northfor Z kilometersbeforereoching the store.Thenshe ridessouthfor to her ount'shouse.Which ó kilometers of the followingdescribesKeisho's velocilyon her trip to the store? @ ó kilometersper hour @ Z kilometersper hour @ ó kilometersper hoursouth @ Z kilomelersper hour north | 8. When you roiseor lower o flog on o flogpole,you ore usingo simplemochine colledo @ lever. @ wheelond oxle. O Pulley' @ inclinedplone. 19. Exploinwhy the onsweryou selected for QueslionI B is best.Foreochof the onswersyou do not select,give o reoson why it is not lhe beslchoice.

i zo. SMffiF

Persuosive

Creotethreepostersthot illustrote ond exploineochof Newton'slowsof motion. Useo slogonor phroseto summor¡ze eoch of the lows. Usethe word inerfío in the firstslogon,occelerofion in the secondslogon,ond ocfionond reocfion in thethird slogon.

437

Ăşr" rot"riol. fromhometo mokeo model oirplone.Try differentmoteriols ond models which to see flieshigherond foster.

Evenin hisown lifetime,IsoocNewton one of history'sgreotest wos considered He hod o deepcuriosityoboutihe scientists. noturolworld. He lookedfor cleorond logicol woys to exploineverythinghe noiiced.He did experiments with lightto exploinhow roinbowsform. He inventedo new kindof telescopeto studythe sky. He put together ideosfromoll differentoreosof sciencein were hisfomouslows very creotivewoys. Amongthe results of motion.Theselows,includinghisdefinitionof force,coused peopleto thinkoboutsciencein o new woy. in Isooc Newtongroduotedfrom CombridgeUniversity Englondin I 贸贸5. Formoreihon 30 yeors,he wos o teocher there.Loterin life,he becomethe heodof Englond'smint, which coinedthe notion'smoney.Portlybecouseof his ic bockground, he wos oble to cotchmonypeople scientif mokingfoke moneyond bringthemto justice. Newton'swork goinedhim the respectof scientists throughoutEurope.Centuries hovepossedsinceNewton's deoth.Yet,eventodoy,histheoriesform the bosisof our | . t. l.l unoersronorno or Ine unrverse.