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Directed Inquiry

Guided Inquiry

Aclivity Flip Chort

Quick AciiviiyTronsporencies

Directed Inquiry

Guided Inquiry

Activity Flip Chorf

Quick ActiviiyTronsporencies

Directed Inquiry

Guided Inquiry

Activity Flip Chort

Quick ActivityTronsporencies

Whot is one woy you cqn determinedensity?

Whot boot design will corry the mostcorgo?

Do woter molecules hove ony spocebeiween them?How do qtoms differ?

How is moller meosured?Whot does on otom look like?How does moiter chonge?Whot ore mixtures?

Whot con hoppen during o chemicolcnonger

How does temperoture offect how long oreoction tokes?

Whot con speed up o chemicol reoction?How con you obsewe evidence of ochemicol chonge?

How con moller chonoe form?Whot ore some chemicol reoctions?How ore chemicol properties helpful?H_ow is technology inuolved in euerydoylite?

Activity Flip Chort How con you use insulolors ondconductors lo moke o gome?How con you mop o mqgnefs mqgnehcfield?

Quick Activit/Tronsporencies Whot is stotic elechicity?

Whot is o simple circuit?Whot does o porollel circuit look l ike?

How con energy chonge its form?

How does light move?

How do woves move?Whot hoppens when you mix cólors?

How is energy reloied to motion?How ore sounds produced?How con l¡qht be bent?Whot is the-rmol energy?

Whot con electricity flow through?

How ore series ond porollel circuitsdifferent?

Con you chonge úe poles of onelectromognet?

Test o Model Airplone

Directed Inquiry

Guided Inquiry

Activity Flip Chort

Quick Activir¡Tronsporencies

Directed Inquiry

\ruroeo rnqurry

Full Inquiry

STEM Project

How con you leorn obout the motion ofo pendulum?

How con you describe motion?

How does inertio offecl motion?Whot forces offeci o poddleboll?

Horv con y_ou moke things move?Whot ore torces?How ore forces reloted trc motion?How do simple mochines moke workeosier?

ENflEreIrffip EhffigpE

element poge 343

OIOÍ| pose 348

prOlOn poge 348

neulron poge 348

electron poge 349

compoundpoge 351

Soturqted poge 3ól

concentrqtedpoge 3ó I

dilule pose 3ó l

tu.#

Explore Whot is one woy you condetermine density?Moteriqls

*6Wñw

I wooden block,

f stick of cloy,

I stick of cloy

¡E¡t@t!

melric ruler

bolonce ondgrom cuoes

colculotor or computer(optionol)

.-

Whor lo Do

Meqsure the length, width,ond height of o wooden blockin centimeters. Find the block'svolume in cubic centimeters.

vol¿¡rne : lengfh x widfh X heighf

Use o bolonce to meosure the moss of theblock. Put the block on one side. Add gromcubes to the other side unii l the 2 sides bolonce.Find the totol moss of the grom cubes. Eochgrom cube hos o moss of 1 grom.

Colculote the block's density. The density is Inumber of groms per cubic centimeter.

densi fg : Í loss+voldne

Repeot steps I to 3 with f of o sfick of clo¡-i of o stick of cloy, ond o grom cube.

Exploin Your ResultsGommunicqte Describe one woy to f¡nd thedensity of on object. Whot must you meqsure?

trn this oclivityyou find thedensi| of eochobject, usingcubic centimetersono groms osthe units ofmeosuremenf.

Tok€ lt to lh€ NetPeorFnslcc8$n€t.cof¡

t@PredictWhen you predicl, you moy osk o quesfion obout whot willhoppen next in o story ond then think of on onswer. After youmoke your prediction, continue reoding. As you reod, considerif ony new informotion supports your prediction. Perhops, newinformotion wil l leod you to moke o different prediction.

Science Fiction Sfory

W**s&e¡rüs*kFor yeors, Rodney worked on building his spoceship.The hordest iob wos finding the right moteriol to usefor the toilfins. They hod to be mode of the densest metol ovoiloble.Unfortunotely, Rodney hod only tlvo moteriols left in his shop. Hehod some squore, thick sheets of titonium ond chromium. Rodneyknew whot he hod to do to moke the rioht choice.

¡¡q{!{i?1X1r*x¡*lrtt}t t*p*}Yt*1:a}i

Apply ltlMoke o grophic orgonizer l ike the one shown. Moke opredicfion obout how Rodney will meqsure the density ofthe moteriols. Communicqte your prediction to o clossmote.

Question Prediction

How wi l l Rodneymeosure the densify?

qu- You Are There!You ore working inside o huge reseorch instrument in oloborotory thot is three stories toll. When your work is done,giont mognets ond other equipment will stort to hum. Tinyporticles, too smoll to see even with o microscope, will zoomthrough the instrument ot super speed. These porticles willsmosh together, forming new types of motter. Scientists doexperiments like these os they study motter. Scientists hovebeen studying motter for centuries. Whot hove they leorned?

!

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Lesson I

What aÍepropertiesof matter? ffi

AII things around us are made with just a few kinds of matter.Each kind of matter has its own set of properties.

ElementsThere 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 substonces with

ordinory physicol or chemicol processes.

Only o few elements, such os gold, ore found in noture inpure form. Most elements ore combined to form the things

oround us. For exomple, rust is o combinotion of iron ondoxygen. Living ond nonliving things ore mode of iust o few

elements combined in mony woys.

Properties of ElementsEoch element hos its own chemicol ond physicol properties.

You con use these properties to identify eoch element. Chemicolproperties describe how o mqteriol chonges into othermoteriols. 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: How mony elemenls ore there? Are things orouno us

The gold in these nuggetsis the pure element.

usuolly mode of pure elements or combinolions of elements?

Why do you th¡nk pons ore mqde of metol?

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343

Weight ond MqssWeight is o meosure of the pull of grovity on

on object. Spring scoles meosure on oblect's weight. Aspring scole hos o spring thot stretches or is squeezedtogether when you weigh on obiect. The omount thotthe spring's length chonges tells the obiect's weight.If on object is too lorge to hong from o scole, you conodd up the weights.of oll the obiect's ports. The totolweight of the ports olwoys equols the weight of thewhole obiect.

Weight chonges when the pull of grovity chonges. Grovityis not the some everywhere on Eorth. For exomple, the pull ofgrovity dec¡eoses slightly os on obiect is Iifted to the top of omountoin. Therefore, the obiect's weight becomes o little less.

Moss is the omount of motter in on object. The omountof moss offects the weight of on obiect, but moss is not thesome os weight. Moving on obiect to the top of o mountoindoes not chonge the omount of motter in on object. Its mossstoys the some. Moss is meosured by using o bolonce, oftenusing units of groms, milligroms, or kilogroms. To find moss,on obiect is ploced on one side of the bolonce. Known mossesore ploced on the other side. When the two sides bolonceeoch other, the totol moss of oll the known mosses equols theobiect's moss.

VolumeVolume is the omount of spoce thot on obiect tokes up.

Cubic units ore used for volume. You con find the volumeof o regulor box by meosuring ond multiplying its length,width, ond height. You con write o formulo using V forvolume, L for length, W for width, ond H for height. Theforrnulo for finding the volume of o box is V : L x W X H.

You con use o groduoted cylinder to find the volume ofo liquid. You con olso use o groduoted cylinder to meosurethe volume of o solid obiect thot ñts in the cylinder ondsinks in woter. First, put o meosured omount of woter in thecylinder. Then put the obiect into the woter. Reod the newvolume. The difference between the t¡,vo volumes is thevolume of the obiect.

By boloncing lhe ioy corwiih known mosses, youcon meosure the cor'smoss io be 8 groms.

Without fie toy cor,the groduoted cylindermeosures 50 millilitersof woler. Wth the cor,the woler level meosures55 milliliters. Whot isthe volume of lhe cor?The volume of solidsore lobeled with cubiccentimelers. One cubiccentimefrer (cm3l is thesome os one millilircr.

344

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This gold bor hoso moss of obout 1025 gor I .025 kg.

Properties of Objecrs ond MqteriqlsHow mony different woys could you describe the physicol

properties of the gold bor obove? There is o differencebetween on obiectt properties ond o moteriol's properties.

You could soy thot the bor's properties include o rectongulorshope with o certoin size ond moss. These properties ore only

true for this bor or other bors iust like it. If you cut or bendthe 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 tomognets. Therefore, these ore gold's properties, not just the

bor's properties. Other moteriol properties include color,hordness, ond texture.

1. JCnecfpoint. Is volume o property of on object, or the motlerthot mokes i t uo?

.) o colculotor or spreodsheet to f ind thepictured obove. Round your onswer

Usevolume of the gold borfo the neorest 0. , ] cm3.

Density ond BuoyoncyDensity 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 thecor on the previous poge by dividing its moss,8 groms, by its volume, 5 cubic centimeters. Thedensity is 1.6 groms per cubic centimeter.

Density is o physicol property of o substonce.Density is the some for o substonce no motterhow much of the substonce is meosured. Forexomple, iron will olwoys hove o density ofabout 7.9 groms per cubic centimeter, no motterhow lorge o piece of iron is meosured. Becousethe density of o moteriol is olwoys the some, itcon be used to help identify o moteriol

Equol volumes of ony two different substoncesusuolly hove different mosses. This meons thotthe two substonces hove different densities. Lookot the pictures below. The boll of cloy hos thegreoter moss ond the greoter density.

This boll of cloy hoso moss of 445 g ondo volume of 195 cm3.Its density is obout2.28#-.

This boseboll hos omoss of I I0 g ond ovolume of 195 cm3.Its density is obout0.5ó#.

I:

Flooting or SinkingAn 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 less thon 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 less thon 1 grom per cubic centimeter.

Oceon woter hos dissolved solts ond other moteriols. Becouse of

this, oceon woter is more dense thon fresh woter. Its density depends

on how much moteriol is dissolved in it.

f' Lesson Checkpoint

l . I f you hod two equolly sized objects, how could you tel l wh¡ch one is moredense?

2. Suppose you hod o moteriol thot is l isted in the density toble on lhe previouspoge. I t f loots in woler but sinks in ol ive oi l . Whot is the moteriol? How doyou know?

Descriptive In your sciencejournol write odescription of on object. Include some properties such os color, odor, ond

hordness. Is i t o gos, l iquid, or sol id ol room temperoture? Do you know how

well it conducts heot or electricity? Would you expect it to floot?

3.

All helium otomshove exoctly2 prolrons ondusuolly hove2 neufrons ond2 elecFons.

The elements inlhis column coneosily lose oneelectron.

Lesson 2

How do atomst . 1comDlne I

Atoms are particles of elements. Atoms combine to formcompounds.

AtomsAn otom is the smollest porticle of on element thot still

hos the properties of the element. Atoms of one element oredifferent from otoms of other elements. Atoms ore too smollto be seen even with o microscope. The properties of otomsdetermine the properties of on element ond how the elementcon combine with other elements.

The otom's center, or nucleus, usuolly hos both neutrons ondprotons. A neutron hos no elect¡icol chorge. A proton hos opositive chorge. An otom is identified by the number of protonsit has. For exomple, oll corbon otoms hove six protons. No

t 35

B

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4

Be

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other kind of otom hos six Drotons.

Chromium is usedin chrome ploting.

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Elements thot ore metols conconduct electricity well.3

21

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Nb

57

1¡r

I

27

CoCoboll

J¿25

Mn2 2 i 2 3 26

Fe

6

24

Cr42

Mo

t 23o

Zn

t 02 8

N¡29

Cu

Pd AgRbLYir.

Gs87

Fr

8'I

TIIh¡'liun

66

Gd

Pb

Nd58

Ce

90Th

5m89Ac

All helium otomshove exoctly2 protons ondusuolly hove2 neulrons ond2 electr.ons.

The elements inthis column coneosily lose oneelectron,

Lesson 2

How do atomsl o ^ lcomDlne f

Atoms are particles of elements. Atoms combine to formcompounds.

AtomsAn qtom is the smollest porticle of on element thot still

hos the properties of the element. Atoms of one element oredifferent from otoms of other elements. Atoms ore too smollto be seen even with o microscope. The properties of otomsdetermine the properties of on element ond how the elementcon combine with other elements.

The otom's center, or nucleus, usuolly hos both neutrons ondprotons. A neutron hos no electricol chorge. A proton hos opositive chorge. An otom is identified by the number of protonsit hos. For exomple, oll corbon otoms hove six protons. Noother kind of otom hos six Drotons.

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Chromium is usedin chrome ploting.

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Elements thot ore metols conconduct electricity well.3 4 5 6 .I-

25

Mn

1 3AI

t 028Ni

27

Co24

Crv22

T¡29

Cu

Rb

YElectrons move oround the protons ond neutrons. An

electron hos o negotive chorge. Electrons moy join or leoveotoms, or be shored between otoms.

The Periodic TqbleElements ore orgonized in o toble colled the periodic toble

of elements. The elements ore orronged in eoch row occordingto the number of protons. Lorger otoms ore on the right sideof eoch row. The columns of the toble ore orronged so thot theelements 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 rightyou will find elements known os noble goses. They do not oftencombine with other elements.

Every element hos o symbol of one, two, or three letters. Onlythe first letter of the symbol is copitolized. Whot elements hovethe symbols C, H, ond Co?

Nonmehls orein the columns tothe right Theydo not conductelectricity well.

r5 lóThe lights in this sign

Phose qt room üemperqfure

controin neon.

Ico. I Not found in nqtureKey:SymbolElemenf nome

The number in eochbox is the number ofprotons in the oiomsof thof element

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I s"lid

.yf Cnectpoint. Describe the periodic toble ondhow it is orgonized.

@ Predict Use the toble lo predict whot otomswould hove similor chemicol propert ies os colcium.Wrile their nomes.

MoleculesAtoms moy combine with other atoms to form

molecules. A molecule is the smollest porticle of osubstonce mode of combined otoms thot hos theproperties of thot substonce. In some molecules,otoms shore electrons. Some electrons no longer gooround iust one otom. They go oround two or moreotoms. These otoms ore then bonded tooether inthe molecule.

Mony substonces ore found in noture os molecules,not os single otoms. Air is o mixture of severol kindsof molecules. It hos oxygen molecules, nitrogenmoiecules, and molecules of other goses. Most oxygenmolecules in oir hove ot leost two oxygen otoms.

Nitrogen molecules olso hove h,yo otoms thot orebonded together. Most of the oir in the otmosphere isnitrogen gos. When nitrogen gos is cooled to -196"C,

it turns into o liquid. Even so, its molecules stillcontoin two otoms bonded tooether.

¡LOmpounosA compound is o type of motter mode of o

combinotion of elements. Atoms of the elements orecombined into molecules. Most things thot you seeoround you ore compounds. Every molecule of ocompound hos the some combinotion of elements.Toke woter, for exomple. Every woter molecule hasthe some three otoms.

o o

An oxygen moleculehos two ofroms.

A nitrogen moleculehos two olroms.

Corbon otroms join iogetherto form grophiie, which isused in pencils.

Imoges of MoleculesNo microscope con enoble o person toocluoily see on otom or molecule. Atomsond molecules ore too smoll for thot. Specioltechnology lets scientists moke imoges ofotoms ond molecules. This technology detectsthe shope of on otom or molecule ond thendrows o picture on o computer screen. Thepictures do not hove true colors. Afoms ondmolecules ore often seen to be well-ordered,os in this port of o grophite molecule.

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Properties of compounds ore different fromthe properties of the elements thot mokethem up. Woter, for exomple is o liquid. Atroom temperoture, hydrogen ond oxygen oreinvisible goses ond do not hove o smell. Sugoris olso mode of otoms of hydrogen ond oxygen,but it olso contoins corbon otoms. Pure corbonotoms con be seen os grophite, or pencil leod.Pencil leod surely does not toste sweet! Yet,when these three elements ore combined in theright woy, they form o sweet, white solid.

Chemicol FormulqsEvery compound hos o nome ond o formulo.

A formulo shows how mony otoms of eochelement ore in the compound. For exomple,woter has the formulo H2O. The "2" after the

"H" shows thot o molecule of woter hos twohydrogen otoms. The O stonds for oxygen. It

does not hove a number ofter it. This meonsthot o woter molecule hos one otom of oxygen.

A corbon dioxide molecule hos the formuloCOr. It hos one otom of corbon ond trvootoms of oxygen. Corbon dioxide does notburn. In foct, it con be used to put out fires.

At temperotures of -78'C, corbon dioxide

becomes o white solid colled dry ice.

t. ¡f Cnecfpoin! In o formulo for ocompound, whot do lhe numbers tel l you?

, 2 .@@Reseorchhow

Glucose is o kind of sugor with theformulo CuH,rQ, The model shows oneform of the glucose molecule. How monyotoms ond whoi elements ore in thismolecule?

Every woter molecule hos tn o hydrogenotoms ond one oxygen olom,

*dry ice, l iquid ni l rogen, or other very coldmoteriqls ore used. Moke o posfer to showwhol you hove leorned.

Dry ice is frozen corbon dioxide. Dry icesublimotes os it worms. It chonges f,ocorbon dioxide gos.

351

Kinds of SqltsCompounds ore not olwoys

formed by shoring electrons. Soltsore compounds in which porticlesore held together by oppositechorges. These porticles moy bechorged otoms or $roups of otoms.Porticles with more electrons thonprotons hove o negotive chorge.Porticles with fewer electrons thonprotons hove o positive chorge.

There ore mony kinds of solts,but they oll hove some things incommon. They oll hove ot leost onekind of metol element ond one kindof nonmetol element. AII solts conform crystols. Crystols ore formedwhen chorged porticles orrongethemselves in o regulor geometricpottern. Solt crystols ore brittle.Generolly, very high temperoturesare needed to melt solts.

Toble solt is sodium ondchlorine. Its crystols look likecubes. Its formulo is NoCl.

Table salt

ss

352

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Properties of SolrsProperties of solts ore different from the

properties of the elements thot went intomoking them. For exomple, most toble solt ismode of sodium ond chlorine. Both of theseelements con be very dongerous. Pure sodiumis o soft, silver metol. Putting o lorge piece

of sodium in woter con couse on explosion.Pure chlorine is o yellow, poisonous gos. Yettogether, sodium ond chorine moke o brittle,white solid thqt we con sofely eot. Pure chlorine

gos in o boitle.¡

*

Pure copper is o goldenbrown meiol. It con eosilybe bent to form pots. It conbe mode into wires.

When copper is used tomoke o solt, its propertieschonge. Copper mokes oblue solt when combinedwith sulfur ond oxygen.

Pure sodium iso soft metol.

Copper mokes o green soltwhen combined with chlorineond woier. Copper sohs orebrittle. They connot be bentor mode inlo o wire os purecopper con,

úleFg¡ cl'es!pri$,l . Compore toble sol t wi th gtucose.

2. Write o porogroph thot tefls how the words moffer,element, atom, crystal, compound, ond molecu/e relole.

¡. @ pred¡ct Suppose o lorge olom bonds wirh o smollotom. Predicl whether the properties of the new moleculewi l l be the some os lhe lorge otom, the some os the smol lolom, or different f rom both otoms.

353

Lesson 3

How do phasechanges occur?

A maturtal is a solid, liquid, or gas because of thearrangement and motions of its atoms or molecules.

Solids ond LiquidsIn Chopter Z you leorned thot woter hos three forms.

Woter is o solid when it's frozen os ice. Woter is o liquidin the oceons. In the oir, woter is o gos. These three formsore colled phoses, or stotes, of motter. The stote of omoteriol ot room temperoture is o physicol property.

The phose of woter or ony moteriol is due to themotions ond orrangements of its porticles-its moleculesor otoms. The porticles ore olwoys moving.

Solids hove o deñnite shope ond volume. The porticlesof o solid vibrote in ploce. In most solids, the porticlesore very close together.

As o solid worms up, it melts. Forces hold the porticlesfoirly close to one onother, but they con move obout.Therefore, liquids do not hove their own shope. Theytoke on the shope of their contoiner. Since the forceskeep the porticles close to one onother, liquids hoveo definite volume.

As liquids get colder ond freeze, theirporticles slow down ond vibrote in ploce.A moteriol freezes of the some temperoturec¡t which it melts. This temperoture iscolled the freezing point or melting point.For exomple, fresh woter freezes when itstemperoture lowers to 0'C. Ice melts whenits temperoture rises to 0'C ond more heotis odded.

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354

Lesson 3

How do phasechanges

-occur?

A material is a solid, Iiquid, or gas because of thearrangement and motions of its atoms or molecules.

Solids ond liquidsIn Chopter Z you leorned thot woter hos three forms.

Woter is o solid when it's frozen os ice. Water is o liquidin the oceons. In the oir, woter is o gos. These three formsore colled phoses, or stotes, of motter. The stote of omoteriol ot room temperoture is o physicol property.

The phose of woter or ony moteriol is due to themotions ond orrongements of its porticles-its moleculesor otoms. The porticles ore olwoys moving.

Solids hove o definite shope ond volume. The porticlesof o solid vibrote in place. In most solids, the porticlesore very close together.

As o solid worms up, it melts. Forces hold the porticlesfoirly close to one onother, but they con move obout.Therefore, liquids do not hove their own shope. Theytoke on the shope of their contoiner. Since the forceskeep the porticles close to one onother, liquids hoveo definite volume.

As liquids get colder ond freeze, theirporticles slow down ond vibrote in ploce.A moteriol freezes of the some temperotureot which it melts. This temperoture iscolled the freezing point or melting point.For exomple, fresh woter freezes when itstemperoture lowers to 0'C. Ice melts whenits temperoture rises to 0"C ond more heotis odded.

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354

The freezing point is different fordifferent moteriols. It is o physicolproperty thot con be used to help tellwhot o moteriol is. The freezing point

of o moteriol does not chonge, no motterhow much moteriol you hove. Thefreezing point of o liquid moy chongewhen things ore odded to the liquid.For exomple, the freezing point of soltwoter is Iowe¡ thon the freezing point

of fresh woter.

Chonging SizeMoteriols chonge size when their

temperotures chonge. The moteriol is notmode o¡ destroyed. The hotter o moteriolgets, the foster its porticles move. Foster-

moving porticles generolly hove morespoce between them. This odditionolspoce couses the moteriol to get o littlelorger. For exomple, putting o metol jor

lid under hot woter mokes the lid hotter.The lid will get o little lorger ond youcon remove it more eosily.

..--.. When moteriols cool, they moybecome o little smoller. Their porticles

move more slowly, ond there is less spocebetween them. Porticles never get coldenough to stop vibroting, though.

I . úCnectppint, Why do moteriols chongesize when they chonge temperoture?

2 @whymigh tyouwont fo consider the mélt ing point of osubstonce before choosing moteriols forfrying pons or engine ports? 1535"C

3s5

l iquids qnd GosesCompored to solids ond liquids, porticles of o gos ore

very for oport. Gos porticles generolly do not offect oneonother unless they collide os they move. If o gas is plocedin o contoiner with no other goses, the porticles will spreodout evenly throughout the contoiner. Therefore, o gosdoes not hove o definite shope or volume. Goses con besqueezed much more thon solids or liquids. This is becousethere is more spoce between gos porticles.

Evoporofing qnd BoilingEvaporotion occurs when

porticles leove o liquid ondbecome o gos. Porticles evoporotefrom the surfoce of o liquid whenthey move upword with enoughspeed. This is how woter puddlesevoporote.

If the temperoture of o liquid ishigh enough, porticles throughoutthe liquid will evoporote too. Asgos porticles move quickly upwordthrough the liquid, bubbles ofgos form under the surfoce ofthe liquid. The boiling point of oIiquid is the temperoture ot whichIiquid turns into gos bubbles.

The boiling point is o physicolproperty of o liquid. The boilingpoint will be the some for o liquidno motter how much is beingheated. Different liquids hovedifferent boiling points. The boilingpoint con be used to help tell whoton unknown liouid is.

When o liquid tums into o gos, the gos tokes up morespoce. This does not meon thot goses hove more motterthon liquids. There iust is more spoce between the porticlesof o gos thon between the porticles of o liquid.

At the boiling point,liquid under thesurfoce turns inlogos. The gos formsbubbles thot rise tothe surfoce. liquidolso turns fo o gosot the sufoce.

356

v

Wolrer vopor is invisible.When you see süeom,whot you ore octuollyseeing ore liny wolerdroplets formed bycondensoiion, '

#.

Porticles of liquids conevoporofe even if the entireliquid does not reoch theboiling point This is whywet clolhes con dry.

CondensqtionCondensotion occurs when o gos

turns into o liquid. This often hoppenswhen gos porticles touch o cold surfoceond their temperoture drops. Theporticles slow down ond ore troppedby the ottroctive forces of the surfoce.As more ond more gos porticles gettropped, they form o liquid drop.The clouds in the sky ond dew on theground form by condensotion.

If the gos toucheso cool sufoce,condensoiion con(xcur.

'&"s#ew

ts*

wiF

$lerql 9t'ee!ipci'!,l. Compore the molion ond spocing of porticles os o moteriol cools

from o gos to o liquid ond then to o solid phose. Do porticles everstop moving?

2. Define ond compore boiling points, melting points, ond freezrngDo¡nls.

Moke o poster with pictures or o Venn diogromlo show how sol ids ond l iquids, or l iquids ond goses ore ol ikeond di f ferent.

Lntorne

357

Lesson 4. r . r - r . |

What aÍe mlxturesand solutions?

Sometimes elements and compounds are mixed together butare not bonded together.

MixturesIn o mixture, different moteriols ore ploced together but

do not bond to form compounds. Generolly, the differentmoteriols keep their own properties. If solt ond pepper oreput together to moke o mixture, the solt ond the pepper donot 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, omognet con seporote iron filings from sond. This seporotionhoppens becouse iron hos the property of being mognetic,

ond sond does not hove thot property. A screen filter con beused to seporote o mixture of pebbles ond sond.

l. The mixture ofsolt, pepper,ond woter ispoured througho filter. Thepepper connot 90through the filterPoPer.

-I !'t@-

Seporoting o Mixture

Suppose you hove o mixture of solt ondpepper thof you wont to hove seporoted.You con do this by using the differentnrooerties of the two moteriols. Soltdissolves in woter. Pepper does not.Peooer would f loot on the woter's surfoce.

tt

Some metols, such os gold, silver, copper,iron, ond nickel, ore elements. Mony metolsore mixtures of elements. For exomple,steel is o mixture of iron ond corbon. Brossis o mixture of copper ond zinc. Bronze iso mixture of metols, mostly copper ondtin. These mixtures ore colled olloys. Theproperties of olloys ore usuolly differentfrom the properties of the originol metols.The properties of the olloys depend on howmuch of eoch metol is used.

2. The solt ond woierposs through thefilter poper.

t .

3. To seporolre he solt fromthe woler, you con use thedifferent boiling poinh ofwof¡er ond solt. This flome ishot enough to boil woter. Theflome is nol hot enough toevoporote the solt, The woterevoporoles ond the solt stoysin the dish.

f Cnectpoint Nome 5 metols thot ore pure elementsond 3 thot ore mixtures.

Norrolive In vour sciencejournol, wr¡fe o story in which o chorocter mokes omixture of food to eot. Be sure to cleorlv stote the steosrequired to moke the mixture.

359

SolutionsWhen dirt ond woter moke o mixture, the dirt will slowly

settle to the bottom. When o pinch of sugo¡ dissolves in 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 -'":Á,;: "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 dissolves is 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 dissolvein o liquid foster by stirring orheoting the solution. Grinding o

solid solute into smoller pieces

will olso helo it dissolve foster.

These solt crystols oremode with the elemenlspotrossium, mongonese,ond oxygen. The solt leovespurple hoils os it dissolvesin wofer ond spreods out.

-"'-"-*w**5

360

A smoll omountof solute is beingdissolved. It willmoke o dilutesolution.

If o solution issoturqied nomore solute willdissolve.

A lorge omountof solute isbeing dissolved.It will moke oconcentroiedsoluiion.

Not oll solutions ore mode by dissolvingo solid in o liquid. Two liquids con moke osolution. A gos con dissolve in o liquid. Forexample, woter in o loke contoins dissolvedoxygen ond corbon dioxide goses. Why wouldit be importont thot these goses ore dissolvedin the woter?

Amounts of SolutesSolubility is o property of o substonce.

Solubility is how much of o substoncecon be dissolved by a solvent ot o certointemperoture. The hotter o solution is, themore solid solute con be dissolved.

Solutions con be described os beingsoturoted, concentroted. or dilute. A solutionthot is soturoted contoins oll the solutethot con be dissolved without chonging thetemperoture" If more solute is odded to osoturoted solution, the solute will not dissolve.A concentroted solution hos so much solutethot it is relotively close to being soturoted.A dilute solution is far from being soturoted.

In mony coses, o moteriol will not dissolveot oll in o porticulor liquid, no motter howhot it is. For exomple, solt will not dissolvein oil.

.úLe"sotr Checkpoint..'l . Could o mixture of pepper ond woter olso be

col led o solut ion? Could o mixture of solt ondwoter olso be colled o solution? Exoloin vouronswers.

2. How con you couse.more solid solute to bedissolved in o l iquid?

3 E@EE&@ Descriptive Observe thepiclures on this poge thot show the moking of osoturoted solution of woter ond o ourole solt. Inyour science journol, write o description ofthe solution's oppeoronce in eoch of the photos.

zoInvestigofe Whot boot designwill corry the most corgo?Think obout whot you know obout density ond the other properties of motler.

Design ond bui ld o boot ihot con corry o lorge omount of corgo without s inking.

Moleriqls Whol to Do

The Problem Design o boot fhot will support the most corgopossible. Foil, cloy, or onother moleriol of your choice con

be used to build the boot. Consider which moteriol would be besl.

Consider different boof designs. Sketch or diogrom your proposed

design choice. Exploin why you picked your design solution.

Identify which moteriols wil l work best for your design.Moke o plon or o procedure.

Construct your model boot. Meosure its length,width, ond height in centimeters.

Test your boot design. Floot your model boot in thetub of woter. Predict how mony pennies your bootwill hold. Add corgo (pennies) to your boot. Recordthe number of pennies you odd before your boot sinks.

,:&foil ond cloy

't

tub with woter

Wmetric ruler

bolonce ond

grom cubes

pennres

You meosuredmoss usingnonslondord ondslondord uni ts.Pennies orenonstondord unitsof moss. Gromsore stondord uni fs.

t@ Ur" o bolonce to meqsure the moss of the corgo

in groms. Record the moss.

'*----. -:-...'-

Did knowing oboof densifghelp gor.t solve goon designpnoblern? Fxploin.

i

lenoth cm

width _ cm

height _ cm

If goon boof wos domoged,how cottfd gou nepoir if?Whof woofd gou ose?

Exploin Your ResultsI . Sketch your model boot design. Exploin

whot coused your boot to sink.

2. Inferpref Dqfq Evoluote your model bootdesign. Wos it more or less successful thonthe designs of the other groups? Exploin.

3. Whot shope, size, ond moteriol mode theboot thot could corry the most corgo?

Amounl of Corgo CorriedWiúout Sinking(number of pennies)

oroms

Review your procedure onddesign with other students.Compore ond controsl yourinvest¡got ion with theirs.Ask yourself ond the othersludents queslions obout howyour procedure ond designcould be improved. Use theircomments to help you mokerevis ions.

o

In eoch l ine plot, notice how the doto spreods out on ihenumber l ine. Notice olso how it clusters in certoin oreos.Then use the toble ond the l ine plots to onswer ihe quesfions.

In which temperoture ronge do the melting points cluster?A. -,l20'C to -80'CB. -ó0'c to -20'cC. -40'C ro 0"CD. 0'c ro 20"c

Q) In which temperoture ronge do the boil ing points cluster?F. I ó0'C to 200'CG. 80"C ro 140'CH. 0'c to 40'cI. *80'C to -40"C

Q Wni.n of the liquids hos on extremelyhigh melting point, compored tothe others?A. proponeB. ch lor ineC. iod ineD. hydrogen peroxide

Q In whi.h temperoture ronge is thegreotest gop between boiling pointsfor these l0 l iouids?F. between

,l20'C ond

,l85'C

G. between -33'C ond Z9'CH. between 17"C ond79"CL between 100'C ond

,l20"C

Copy the l ine plots on lhe previous poge.Find the melt ing point ond boi l ing point for5 other substonces. Moke o toble ond oddthe doto to the l ine plots.

orom {p .348)

compound(p .351)

concentroled(p .3ó1)

di lure (p. 3ó1)

eleclron (p. 3a9)

elemenl (p. 343)

neulron (p. 3aB)

proton (p. 348)

soturoted (p. 3ó I )

Use Vocqbulory

Use the term from the list obove thot beslcompletes the sentence.

I . A(n) - is in the nucleus of on otomond hos o posi t ive chorge.

2, A(n) - is in the nucleus of on otomond hos no electr icol chorge.

3. Alnl is oort of on otom ond hos onegotive electricol chorge.

4. A solut ion is - i f i t hos o lorgeomount of solute in comporison with theomounl of solvent.

5. A(n) - solut ion hos l i t t le solute incomporison with the omount of solvent.

6. A solut ion is - i f i t contoins ol l thesolute thot con be dissolved ot the time.

7. There ore more thon 1 00 types of motter,

eoch col led o(n)

8. The smol lest port ic le of on element is o(n)

9, Elements combine to form o(n)

i Exploin ConceptsExploin the difference between on otomond o molecule.

Whot is the difference between o mixtureond o solut ion?

Exploin how motler chonges f rom o sol idto o l iquid ond then lo o gos.

I3. Infer You mix oi l ond vinegor for o soloddressing. After o few minufes, the oi l hosseporoled ond is f loot ing. Infer whichhos the greoter densi ty-oi l or v inegor.Exploin.

Use the following toble for Question I 4.

Clossify woter ond sodium chloride(toble solt) by tel l ing which column eochbelongs in.

ro.

I l .

12.

Held Togetherby Opposite€horges

i

15. Form Gluestions You hove o dividedbox with lobeled comportmenls. Eochcomportmeni hos o somple of o differentelement. You drop the box ond spill olllhe somples on the floor. Form questionsto help you put lhe elements bock in theright comporf ments. Form ot leost fourquestions.

@ Predictló. A plostic block hos sides thot meosure

4 centimeters, 2 centimeters, ond3 cenf imelers. I ts moss is 19.2 groms.Predict whether the block will floot inwoter. Will it floof in olive oil? Gotherinformotion before moking yourpredictions. Fill in the boxes oerow.

Informolion

H)-

Test PrepWhich of the following is o mixture?@ gold@ steel@ iron

@ nickel

The omount of motler in on object is its@ weight.@ densily.@ volume.@ moss.

| 9. Exploin why the onswer you selecfedfor Question I B is best. For eoch of theonswers you did not select, give o reosonwhy it is not the besl choice.

; 20. E@@DescripriveChoose on item f rom lhe clossroom onodescribe ot leost five physicol propefiesof the item.

17.

r8.t

y

'

v

!t

96?

-l

IThe worst grode Noncy Holl ever got

wos in science. She wos in fourth grode.She thought science wos boring. Thot chonged

in sixth grode. Ms. Holl hod o wonderful scienceteocher who inspired her to do experiments othome. When she got older, she studied spoce sciencel|in college. Now she is o reseorch scientist ot NASA.She does reseorch on f lu ids-goses ond l iqu ids.

Noncy Robel HollShe leorns how they behove in spoce. r\qncy KqDer nqn

Ms. Holl conducts ""perimenis

in which fluids s works wilh ooses

for the moment, to be weightless, os they *orl¿ u"J'l ond liquids'-

spoce. These experiments ore done ot NASA ond orerepeoted mony times. In this woy, scientists ensure thot

ihe results ore consistent. Then the experiments moy berepeoted in spoce-on rockets, on the spoceshuttle, or ot the Internoiionol Spoce Stotion.

Ms. Holl loves working os o spoce scientist forNASA. But when she first went to college, she stortedout in computer progromming. Ms. Hol l

switched to spoce science, becouse thot iswhot she reollv wonted to do. She odvises

young people to work hord to pursue theirstrongest interests.

Observe how drops of woter interoct. Fillon eyedropper with woter. Count howmony drops con fit on o penny before thewoter overf lows.

2Mg

*

f,PMognesium

+

o,

'e "t'

Oxygen

------> 2MgO

_ * * -

370

Mognesium Oxide

€ho&r f?V*ahulory

physicol chongepoge 325

chemicol chongepoge 375

combustion pose377

reqctqnl poge 3ZB

product pose 328

chemicql equotionpoge 328

polymer pose 388

Explore Whot con hoppenduring oMoleriols

2 cups ond poper towel

ffiw:lroom+emperoture woter

ond groduoted cylinder

#".#J:- !l . ! * ; . * ¿

lhermometer ond

3 Alko-SeltzeP ioblets

\." \s*cup with 3 spoonfuls of

boking sodo ond cup with3 spoonfuls of colcium chloride

timer or stopwotch

{or clock with o second hond)

After you collectdotc, you use postexperience lo helpevoluole the dotoond moke occuroteinferences.

chemicol chonge?Whql to Do

Put 50 mL of woter ond othermometer in cuo A. After1 minute, record the temperorure.

Add 3 Alko-Seltzer@ toblersto cup A. Woit I minute.Record the temoeroture.

Do nof tosfe fhe toblets,the powdens, on fhe liqrids.

Wipe off the thermometer with opoper towel. Put 50 mL of woter ondthe thermometer in cup B. After1 minute, record the temperoture.,.

Add the boking sodo ond colciumchloride to cup B. Woit I minufe.Record the temoeroture.

If o neocfion prodoces heof, fhefempenofone rises. Thenmol enengg isgiven off. Less enengg nenroins. Bg osing othenmornefen fo rneosone fhe ternpenofonechonge, goo con fell if enengg is losf ongoined doning o neocfion.

Exploin Your ResultsUse the dofo you collected io moke oninference. In which reociion wos energy lost?

Weon sofetggoggres.

t

:l.

f

ü

a

.r t!.¿

¡"¿?nlDrow Conclusions

Your science book is pocked with focts. You put these foctstogether with your own knowledge obout the world to drqwconclusions. Drowing conclusions helps you shorpen yourunderstonding of science.

. Reod the focts oresented in th is orticle.

r Think obout whot you olreody know obout the topic tomoke qn inference obout it.

o Use the science focts ond your own knowledge to drowo conclus ion.

Cooking Article

OcldngErocüBokers use yeost to boke breod. They mix theyeost with worm woter ond sugor. Then theyodd flour. The yeost digests the sugar ond givesoff bubbles of corbon dioxide. This mokes thebreod dough rise. The heot of boking kills the yeost. Look ot theholes in q slice of breod. Whot conclusion con you drow obout it thotrelotes to the yeost ond its octivity?

iri{{{rr.a{r, | ,{i},,*rr:r} ,¡

Apply It!Moke o grophic orgonizerl ike the one shown here.Write down your conclusion.List the focts from the orticre

t t t lono your own Knowreogethot led you to drow thisconclus¡on.

Foct

ffi-Focl

ffla

Conclusion

{D Y@r Ame TheregWith oir tonks stropped securely to your bock,you swim down 40 meters toword the oceonfloor. It is dork, but you hove o floshlight. Youcost its beom on o sunken ship, lying tilted otthe bottom of the oceqn. The ship hos been herefor over six decodes. It hos chonged o greot deolsince it sonk. The once sturdy wood is soft withrot. The metol no longer gleoms but flokes withrust. The oceon is slowly chonging the moteriols

1Lesson I

What aÍe chemicalchanges?

Matter changes all the tíme. Some changes are physical

chanoes. Others are chemical chanaes.

Physicol ond Chemicol ChongesMotter con undergo physicol chonges ond chemicol

chonges. When o physicol chonge hoppens, the moteriolremoins the some. Some physicol chonges ore changes inposition, size, shope, volume, ond phose of motter. For

exomple, falling roindrops con freeze to form sleet. Eventhough the roindrops ond the sleet differ in size, shope,volume, ond phose of motter, they ore both still the someessentiol substonce: woter.

On the other hond, o chemical chonge hoppenswhen one substonce or kind of motter

changes into qnother completely differentkind of motter with different properties. Forexomple, the shipt wheel in the picture wosmode 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 properties of rust ore differentfrom those of iron.

l. ..ú9,h:g!.Coint, Whot is fhe differencebetween o chemicol chonge ond o physicolch o nge?

2 EM@DescriPtive Think of otime when you've coused o physicol chonge,o chemicol chonge, or both. Describe wholhoppened in your science journol.

This ship's wheelhos undergonechemicol chonges.

.rrra?t?¡:-.

Cors rust when ochemicol chonge turnsshiny iron into dullbrownish-red rust.

This ontocid toblet givesoff corbon dioxidegos os it undergoes ochemicol chonge.

The burning logs giveoff heat ond light oso chemicol chonge isoccurring.

Evidence of Chemicol ChongeWhen o chemicol chonge occurs, otoms reorronge

themselves to form different kinds of motter. It is notolwoys eosy to tell if o substonce hos chonged chemicolly.Some signs thot o chemicol chonge hoppened ore ochonge in color or thot o gos or o solid formed.

As you hove reod, iron undergoes o chemicol chongewhen it rusts. A sign of this chonge is the change incolor-the groy metol turned brownish-red.

Dropping some kinds of ontocid toblets in woter olsoresults in o chemicol chonge. The toblet fizzes, giving offmony tiny bubbles. These bubbles ore corbon dioxide gos.A solid ontocid toblet does not contoin gos. This gos formswhen 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 thetree chonges. Crystols form, clinging to the wire bronches.The formotion of this solid materiol is evidence thot ochemicol chonge hos token ploce.

d

These copper wireshove been orronged inthe shope of o leoflessevergreen tree.

coPPerhee is plocedinlo o solutionof chemicols.

376

bChemicol Chonges ond Energy Ghonges

During some chemicol chonges, bonds between otomsor molecules breok. During other chemicol chonges, newbonds 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 process of combustion. During combustion, theburning log gives off energy. We detect the energy os the heotond light of the fire. In other reoctions, energy moy be given

off in the form of electricol enerqy.

¡f L."sott checkpoint,

l . Lisl three types of evidence of chemicol chonge.2. Compore the second ond third piclures of the copper tree

experiment. Aside f rom the forming of solid crystols,whotother evidence of chemicol chonge in the l iquid do you see?

3. '@

Drow Conclusions When you cook on egg, do youthink o chemicol chonge occurs? Why or why nof?

\

A chemicol chonge hoscoused solid crystolsto form on the copperhee. These crystols oremode by o chemicolchonge thot hoppenswith fie copper ond ochemicol in the solution.look ot the top of fietree. Why hosn't itchonged?

377

Lesson 2

rffhat are some kindsof chemical reactions?

Chemical changes occur during chemical reactions.There are several different kinds of chemical reactions.

Chemicql EquotionsDuring o chemicol reoction, one or more substonces chonge

into other substonces with different chemicol ond physicolproperties. A substonce used in the reoction is colled oreoctont. A substonce mode during the reoction is colledo product. During the chemicol reoction, the reoctontsundergo chemicol chonge. Their otoms reorronge toproduce the products.

A speciol kind of "sentence," colled o chemicalequction, shows whot hoppens during o chemicolreoction. The reoctonts ore listed on the left sideof the chemicol equotion. Ihe products orelisted on the right side. An orrow betweenthe reoctonts ond products is sometimesreod os "mokes." It is similor to onequol sign in o moth equotion.

In the picture ot the right, electricityflows through woter. This cousesthe otoms in the woter moleculesto reorronge ond form hydrogenond oxygen goses. Woter isihe reoctont. Hydrogen ondoxygen goses oreproducts. The equotion

reoction is:

Test tubescollectbubbles.

for this reo21120 _____>

cotL, -.

Reoclonls

2H, * O,

opeb. a 't

Hydrogen Oxygen

Products

378

2Mg

{t{ü

Mognesium

^n,il*d@.*?

*d ,

Reo(lqnts

Mognesium is o groy metol. If it reoches o 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 Droduct of the reoction.

Motter Is AIwoys ConservedMotter 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 goses thot floot

from the oven, moking the coke smell so good.

I . úCnecrpoint-: Whot do chemicol equotions show?

2 EM@ Look ot the chemicol equotion on the to'pof this poge. Suppose you stort with 100 otoms of mognesium.How mony molecules of oxygen ore needed to reoct with o

the moonesium?

Mognesium metolis groy.

Mognesium con combinewith oxygen. They orereoclonts. Bright light ondheot show thot o reqctionis hoppening.

2MgO

Mognesium Oxide

Producl

The product is mognesiumoxide. This producl hosproperties thot ore differentfrom the properties of thereoclonls.

Motler isconserved whenyou boke o coke.

O,

\

t , 1

Oxygen

379

Types of Chemicol ReqcfionsIt 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 conuse trucks ond troilers os models of otoms in reoctions. Threekinds of chemical reoctions ore described here.

Breoking Aport, Joining Together,Switching PIoces

In one kind of reoction, compounds split oport toform smaller compounds or elements. This is colled odecomposition reoction. To picture o decomposition reoction,think of o truck unhitching from the troiler. This is the kindof reocüon on poge 378. In this experiment, electricity couseswoter to breok oport to form hydrogen ond oxygen goses.

In onother kind of reoction, elements or compounds cometogether to form new compounds. This is colled o combinotionreoction. To picture o combination reoction, think of o truckconnecting to a troiler. This kind of reoction occurs when iron ondsulfur come together to form o compound colled iron sulfide.

I

When sugoris heocd, itfurns intocoromel. Duringport of thisdecompositionreoction, sugormoleculesbreok oport.

Before úe combinotionreoclion, iron is o greymognetic moteriol.

Sulfur is o yellow powderlhot 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 burningof 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 longmolecules ond oxygen molecules breok oport ond rejoin in new

comoounds such os corbon dioxide ond woter.

A replocement reoclionoccurs when wox burns.

X[ Lesson Checkpoint,,

l . Descr ibe three kinds of chemicol reocf ions.

2. In the chemicol reoction described on poge 379,mognesium reocfs with oxygen gos. Whot kindof chemicol reoct ion is th is? Exoloin.

3 E@Besidesthe imogeof thetruck ond troiler, whot other models forreoctions con be used? Drow oicturesto show how your model works for|wo different k¡nds of chemicol reoctions.When iron ond sulfur ore

heoted together, they reoct.

Afier they reocl, iron ondsulfur moke o compoundthot is not mognetic.

Ihe fossil does notreoct quickly withvinegor, but thelimesione oroundthe fossil does.Whot evidence ofthis reoction conyou detect?

Lesson 3

How are chemicalproperties used?

Chemical and physical properties are helpful in manyways. They can be used to separate mixtures and to helpidentifu materials.

Seporoting MixturesSubstonces in some mixtures con be seporoted by

physicol meons. As you reod in Chopter 11, you conseporote solt ond pepper becouse they hove differentphysicol properties. Substonces moy olso hove differentchemical properties thot con be used to seporote themfrom one onother.

Scientists who study dinosour fossils ond other fossilsuse chemicol properties to seporote mixtures. Fossils oreoften scottered throughout limestone. It con be difficultto chip limestone off o fossil without domoging thefossil. However, limestone con be dissolved by vinegor.A bubbling reoction occurs. Fossils, which ore mode ofo different kind of rock, do notreoct with vinegor os quickly.So scientists sometimes usevineoor or similor chemicolsto seporote fossils from rock.

f,

r1

Seporoting Metols from Ores" Ores ore rocks thot include metols combinedwith other substonces. People rely on chemistry toreleose metols from their ores. For example, ironore contoins iron oxide. Heoting iron ore in a hotfurnoce with solid corbon ollows the iron toseporote from the oxygen in the ore. The result ispure iron ond corbon dioxide. This process worksbecouse iron hos the chemicol property of bondingto oxygen less strongly thon to corbon.

In this blost furnoce, iron isseporoted from iron ore. Theprocess relies on the differentchemicol properties of ftesubstonces heo¡ed here.

382

Sometimes chemicol properties con be used toseporote elements from solutions. For exomple, leodcon be token out of o solution thot contoins woter,leod, ond other moteriols. The solution is poured intoo contoiner with o second solution thot contoins iodine.Both solutions ore cleor liquids. As soon os the solutionsmix, the leod reocts with the iodine. These tlvo elementsform o compound colled leod iodide. This is o yellowsolid. The leod iodide con be filtered out of theliouid to remove the leod from the solution.

The solution is poured into osecond solution thot conf,oinso compound of iodine.

The leqd combines withthe iodine ond forms oyellow solid. This solid conbe filtered io remove theleod from fhe solution.

l . úCnecfpo¡nt, How conchemicol properties be used toseporote subsfonces in o mixtureor comoound?''@

Dro* Conclusions Thechemicol reoct ion for pur i fy ing i ron

This solution contoinso leod compound.Chemicol propertiescon be used toremove the leod fromthe solution.

2.

ore looks l ike this:

2FeO+C '2Fe+CO2

t7 iron corbon iron corbonoxide dioxide

Review the different kinds of reoctionsdiscussed in Lesson 2. Whot k ind ofreoction is shown here?

383

Idenrifying SubstqncesScientists use physicol properties, such os density, to

identify substonces. They can use chemicol properties forthis purpose, os well. The pictures below show one woyscientists do this.

Acids ond boses ore two common types of substonces.Lemon iuice ond vinegor ore ocids. Household cleoners moycontoin bases. Strong ocids or boses will reoct with othermoteriols more eosily thon weok ocids ond boses do.

Acids ond boses hove chemicol properties thot helppeople identify them. Acids ond boses eoch reoct withchemicols in speciol poper colled universol indicotorpoper. These reoctions produce color chonges in the poper.Substonces thot are strong ocids will turn the poper red.Strong boses will turn the poper purple. Weoker ocids orboses will produce different colors. Other kinds of popersond liquids will chonge colors becouse of ocids or boses.

You cannot identify o substance iust by using universolindicotor paper or similor products. Mony different ocidswill turn indicotor poper red. Mony boses will turn it purple.Indicotor poper is helpful, though, in providing more cluesfor people to use in identi$ring o substonce.

Fruits such os orongesond lemons contoin ocid.

Soops moy confroinboses.

r:!

Rqinbow Strip of Indicotor Poper

Boses cquse universol indicotor poper to turn shodesof green, blue, ond purple. Acids moke úe poper turnoronge or red.

H):drochloric acid Tap water

Strontiumchloride

lemon juice fromoio juice

Boriumchloride

Colciumchloride

Potrossiumchloride

These wires weredipped in differentmetol solts. Whenthe metol isheoted to o highfremperoture, thecolor of the flomecon be used ioidentify the solt.

Scientists sometimes use flome tests to identiff o substonce.

In o flome test, o moteriol is heoted to high temperatures in

o flome. Different substonces wiII couse the flome to hove

different colors. When these flomes ore studied closely with

loborotory equipment, the substonces con be identified. Whot

color flome does colcium chloride qive off?

yf Lesson checkpo¡nt,

l . How might o scient ist dist inguish fhe fol lowing compounds: stront iumchlor ide ond ootossium chlor ide?

2. Whot color do you th¡nk indicotor poper would turn if it were dippedin shompoo? Exploin your onswer.

3 g!@ffiFiDExpository Use whoi you leorned oboutf lome tests to exploin how compounds thot contoin stront ium ondborium could be used in fireworks. Write your explonotion in yoursciencejournol.

seowoler household ommonio

Liquid soap Household cleaner

385

How is chemical technologyused in our lives?

Lesson 4

Chemists have made important discoveries that have improved health,nutrition, agriculture, transportation, and many other parts of our lives.

Chemistry qnd Heqlrh

(

)

!!

Antibiofics ondother medicinesore often incopsules. Thecopsules ore modeof chemicols thotdissolve in yourdigeslive system.

Mony vitomin pillstodoy ore modeby chemists.

Yeors ogo, people sometimes died from simple cuts. If o cutbecome infected with bocterio, the infection could spreod tothe blood. This kind of infection wos very serious. No medicinecould cure it.

In 1928, British scientist Alexonder Fleming mode onoccidentol discovery. It eventuolly led to the development ofvery powerful medicines to treot infections. Fleming grewbocterio in dishes. When mold grew on one of his dishes,Fleming noticed thot the bocterio neor the mold died. The moldproduced a substonce thot killed the bocterio. Fleming colledthis substonce penicillin ofter the nome of the mold. Chemistsseporoted penicillin from the mold ond found ways to moke it.Mony kinds of infections could be treoted with penicillin. Bythe mid-l940s, this chemicol become o medicine thot sovedmony lives. Todo¡ mony other medicines olso kill bocterio.These medicines ore colled antibiotics.

!a

a

Bocüerio oregrowing in opetri dish.

Chemisrry ond FoodsYeors ogo, some people suffered from o diseose thot ot first

mode their skin turn red ond scoly. Other people suffered fromo diseose thot mode the tonoue smooth. Another diseosegove children bodly formed bones, including legs thot

bowed out or knees thot knocked together. In the

eorly 1900s, scientists found thot eoch of these

diseoses could be prevented if people ote certoin

foods. Chemists identified the substonces in foods thotprevented these diseoses. They nomed these chemicols

vitamins. Todoy, vitomins ore odded to mony foods thot we

eot in the United Stotes. The diseoses coused 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 Stotes hove been

oble to grow more food thon before. This hos lowered the

cost of mony foods.

Mold is plocedin o dish ond itolso grows.

L 1|Checkpoin! Whof ore ontibiotics ond how hove lhey.improved heolth?

2 g@ffi@ Persuosive As you leorned in Chopter ó,overuse of ontibiotics con couse them to stop working to cure diseoses.However, mony of todoy's soops hove ontibiotics odded to them.Wrile o short editoriol on whelher you think soops thot you use everydoy should or should not contoin ont ib iot ics. Exploin your reosoning.

ffr'p' 'r Boclerio connot

Differentfertilizers oddpotossium,nilrogen, ondphosphote tothe soil. Thesechemicols helpplonts grow.

Bocfrerio con

survive neor themold.

347

Chemisrry qnd New Mqteriqls

388

Mony moteriols you use every doy come from noture. Forinstonce, the cotton in ieons comes from o plont. The woolin o sweoter is sheep's hoir. But some ordinory moteriols orenot found in noture. Scientists invented them. For exomple,nylon in iockets ond other clothing, plostics in toys ond monyother obiects, ond even concrete in sidewolks ond roods oreoll moteriols thot people mode.

Mqteriqls for Everydqy UseIn the 1800s, scientists begon working to moke o fiber to

use insteod of silk. Silk is strong, soft, smooth, and comfortobleto weqr. To make silk though, people hod to get threods fromsilkworm cocoons. Thot is one reoson silk hos been expensive.In the 1880s o French scientist mode o soft, shiny fiber thatwos like silk. The only problem wos thot it eosily burst intoflomes. In the mid-1930s, on Americon chemist reochedsuccess. His silklike fobric, colled nylon, wos perfect forstockings. It soon wos used for moking ropes, nets, fishingline, ond mony fobrics.

Nylon is o polymer-o lorge molecule mode of monyidenücol smoller units connected together. In nylon, eoch unitis mode of six corbon otoms, seven hydrogen otoms, ond onenitrogen otom. A polymer moy hove thousonds or millionsof units in o single choin.

Plostic is onother type of polymer thot scientists leornedto moke in the loborotory. One kind of plostic molecule hoso 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 long-losting. They ore olso foirly cheop to moke.

Mqteriqls for BuildingYou might think thot concrete is iust sond mixed with woter.

But the moin ingredient is cement-o humon-mode moteriol.To moke concrete, cement is mixed with grovel, sond, ondwoter. Cement sets during o chemicol reoction. The resultingconcrete is rocklike-hord ond longJosting.

t :

The solufion in thisbeoker is drown oul tromoke nylon threod.

Plostic is used noljust for mokingloys. This ortificiolheort is mode ofmetol ond plostic.

Chemists hove mode different kinds of concrete to usein different woys. They odd certoin chemicols so concretecon horden in very cold weother. Other chemicols giveconcrete extro strength. Sometimes lorge omounts of tinyflbers ore mixed in concrete to moke it stronoer ondhove fewer crocks.

o¡l

Chemistry ond TrqnsportofionHowever you got to school today, by bus, by cor, by bicycle,

or even on foot, you hove chemists to thonk. Advonces inchemistry hove given us o lorge supply of rubber both for ti¡esond for the soles of shoes. Noturol rubber comes from plonts. Itbends eosily ond is waterproof. But untreoted rubber becomesbrittle ond crocks in cold weother. It melts ond becomes gooeyin hot weother. In the 1800s, chemists experimented withnoturol rubber. By heoting it ond odding sulfur, they modethe rubber duroble ond usoble yeor-round. In the mid-1.900s,chemists developed o woy to moke ortificiol rubber in foctories.

We owe our modern tronsportotion system not only to rubberbut olso to petroleum, or crude oil. Petroleum is o mixtureof mony different compounds. Gosoline, kerosene, diesel oil,ond lubricoting oil ore some of the compounds in petroleum.These compounds ore seporoted ot lorge oil refineries. Gosolineis one of the smoller molecules in petroleum. Chemists hovedeveloped woys to breok down some of petroleum,s lorgermolecules to form gosoline. In this woy, we con get moregosoline from eoch borrel of petroleum.

The gosoline thot mokes thismofrorcycle trovel ol greoi speedwos seporobd or converied fromother compounds in petroleum.

Mony of the body ports oremode of plosiic.

The tires for thismolorcycle were modefrom heoting o mixlureof rubber ond sulfur.

d

t

il

!,

I

use physicol ondchemicol chonges inpeholeum tro mokemony products.

t. ,$C,!9c¡p9¡¡tl How did scienrists working with rubber ondpetroleum help our modern lronsporfotion system?

2 @Use fhe Internet fo leorn obout reseorchthot scienfists ore doing on superconducfing ceromics for use invery fosl troins (colled moglev troins). Summorize whof you reornin o porogroph.

Chemislry qnd Technology

Korl Benz develops one of thefirst cors thot runs on gosoline.

ra39Chorles Gooüeor discovered oprocess he colled vulconizotion thotmode rubber stronger.

ra59The first oil well in the UnitedStotes is drilled. The first oilre{inery is built ot obout this time.

lgtot'Ammonio wos first mode withnitrogen from the oir. It wos loierused os fertilizer.

r9t2aAlexonder Fleming discoverspenicillin.

t935The first nylon fiber is mode byDr. Wolloce Corothers qnd hisloboroiory ieom.

Chemicqls ond SofetySome chemicols moke life less dongerous for us. For exomple,

scientists hove leomed how to use chemicols, such os chlorine,

to kill germs in drinking woter. This sonitotion meosure helps

prevent woterborne diseoses. Before chemists developed modem

woter treotment methods, these diseoses coused 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.. You need to look corefully otworning labels on chemicols. By heedingthese wornings, you con help protect yourself,your fomily, your pets, ond your home.

You moy hove cleoning supplies, such osbleoch, ommonio, oven cleoner, ond othersin your home. Before you use ony of thesecleonsers, reod the directions. The directionsmoy tell you to wear gloves to protectyour skin. They moy tell you toweor goggles to protect youreyes. They moy tell you to keepo window open for fresh oir. Thiswill help protect your lungs fromdongerous fumes thot come fromthe products.

You olso need to be very corefulnot to mix ony cleoners, such osbleoch, ommonio, droin cleoners,ond others. Doino so con cousedongerous chemicol reoctions which'cqn leod to lung domoge, burns,éxplosions, ond even deoth.

Reoding o lobel con tell you if thesubsionce in o bottle is poisonous ortoxic. Respect lobels! They ore thereto profecl you.

/

-!l

392

l .)

Lobels

Poisonous

Conosive

Flammable

Radioactíve

Why is i t importont to ovoid mixing household cleoners?Whot is o polymer?'@

D.orrt Conclusions Of oll the technologicol developmentsdiscussed in this lesson, which one do you think most improvedhumon I ives? Exploin.

offect how long o reoction tokes?An Alko-Seltzer@ foblel bubbles ond f izzes when dropped inlo woter.In this octivity, you will find out how lemperoture offects how fost lhis reoction occurs.

Moteriqls llfh¡r+ l¿r ll¿r

3 Alko-SeltzeP toblets

füthermometer ond

l¡mer or stopwotch(or clock with o second hond)

J CUps

-L-

-lÑ-

ice-cold woter,roomJemoeroture woler

worm woler

**!t

I

Whqr to Do

.When you do onoctivity, corefullyselect woys to helpcollect, record,ond repori yourdofo. You mightwish lo use grophs,lobles, chorts,diogroms, ordrowings.

t" Drop on Alko-Seltzer@ toblet into the cup.Meosure ond record the number of secondsrequired to complete the chemicol reoction.

'T

Repeot steps 1 ond 2 withroomJemoeroture woter ondworm woter. Moke o chort tohelp collect your doto.

To help collecf, necond, ondneponf goon dofo, ¿se o chontlike this one on select o diffenenftoble, chonf, on diognorn.

Exploin Your Results1 . Report the doto you collecfed. Think of o

woy to show the times required to completethe chemicol reoctions. You could moke o borgroph, o l ine groph, or o d iogrom. You moyselect o different woy to report your doto.

2. Xnfer How does temperoture offect how longo chemicol reoction tokes?

(io Further

Wqler Temperqlurerc)

Room-lemperqture

woler

If you repeot the octivityseverol times, will you getsimi lor resul ts? With yourteocher 's permission, mokeond corry out o plon to f indout. When f in ished, give onorol report io your closs.

You hqve leqrned qbouf the Low of Conservqlionof Mqss. If soys lhqt, in q chemicol reqction, lhefofql mqss of the reqclqnts equols the tofol mqss ofthe producfs.

If ó groms of hydrogen is combined with oxygen to form54 groms of woter, how much oxygen wos used?

You con find the onswer by writ ing ond solving on equotion.Remember, when you solve on equotion, you ore f inding onumber thot wil l reploce o symbol ond moke the equotion true.

Let x represent the number of groms of oxygen.

groms o[ groms of groms ofhydrogen oxygen woter

6+x=54

The equotion 6 + x = 54 is true only if the symbol x isreploced by o certoin number.

fry 45. Does ó + 45 equol 54? No. 45 is too smoll.Iry 48. Does ó + 48 equol 54? Yes.

x= 48The number 48 con reoloce x to moke 6 + x = 54 rrue.

The omouni of oxygen used wos 48 groms.

t-

Solve eoch equotion.

,W"*2s=78 @tZS+n=ó00t{p rez-x=e7 G} n*72s=Boo

Write ond solve on equotion to f ind eoch onswer.

ff i f ZOO g of sodium is combined with chlorine togive 508 g of sodium chloride, how much chlorinewos used?

ffi ft SOO g of woter is decomposed to give 40 9 ofhydrogen gos,. how much oxygen gos wil l be mode?

Find five household products thot orechemicol compounds. Exomples includetoble sol t , boking sodo, v inegor, bleoch,ond detergent. Reseorch to find thechemicol elements thot moke up eochcompound. For exomple, woter is modeup of hydrogen ond oxygen. Moke o tobleshowing whot you found.

chemicol chonge physicol chongelp.375) lp.3751

chemicql polymer (p.3BB)equotion (p. 378)

combustion

!p.377)

producl (p. 3ZB)

reoctonl (p. 378)

Use Vocqbulory

Use the term from the lisl obove thot bestcompletes eoch sentence.

l . A - hoppens when one substoncechonges into onother su bstonce.

2. A substonce thol is chonged in o chemicolreoction is colled o -

3. A Iorge molecule formed from smol lerident icol uni ts is col led o -

4. When objects chonge by teoring,crushing, or melt ing, but do not chongeinto di f ferent substonces, o - hosoccurreo.

5. The process of burning is colled

6. A substonce lhot forms dur ino o chemicolreoction is colled o

7. A speciol sentence thol describes whot'hoooens in o chemicol reoct ion is col led o

i Exploin ConcepfsI 8. Exploin how rust forms.

Controst physicol chonges with chemicolcho nges.

Exploin how chemists improved noturolrubber so thot it become o more usefulmoter iol .

I l. €onclude With o cold sports pock, youtwist the pock, cousing two substoncesto mix. The sports pock quickly becomescool. Hos o chemicol reoction occurred?Exploin.

I2. Infer Refer to the piclures of the flometest on pqge 385 ond reod the coptions.How do you know thot chloride gives offno strong color in this test?

13. Model Moke o model out of cloy toshow how otoms combine to form sodiumchlor ide (NoCl). Moke onother c loymodel for silver nitrote (AgNO3). Useboth models to show whol hoppens whensodium chlor ide ond si lver ni t rote reoct in

o replocemenl reoction.

9.

lo.

:/

f

't

Use Vocqbulorychemicol chonge physicol chonge(p .375) (p .325)

chemicol polymer (p. 3BB)equolion {p. 3ZB)

producf (p. 378)combustion

reoclqnl (p. 3ZB)lp. J/ / l

Use the lerm from the list obove thot bestcompletes eoch sentence.

I . A _ hoppens when one substoncechonges into onother substo nce.

2. A substonce thot is chonged in o chemicolreoct ion is col led o

A lorge molecule formed f¡om smol lerident icol uni ts is col led o - .

When objects chonge by teoring,crushing, or melt ing, but do not chongeinto different substo nces, ooccurred.

5. The process of burning is col led

A substonce thot forms dur ing o chemicolreoction is colled o -.

A speciol sentence thot describes whothoppens in o chemicol reoct ion is col led o

i Exploin Conceptsi 8. Exploin how rust forms.

9.

ro.

Controst physicol chonges with chemicolcnonges.

Exploin how chemisls improved noturolrubber so thot it become o more usefulmoter iol .

Conclude With o cold sports pock, youtwist the pock, cousing two substoncesto mix. The sports pock quickly becomescool. Hos o chemicol reoct ion occurred?Exploin.

Infer Refer to the pictures of the f lometest on poge 385 ond reod the coplions.How do you know thot chloride gives offno strong color in this test?

Model Moke o model out of cloy toshow how oloms combine lo form sodiumchlor ide {NoCl). Moke onother c loymodel for silver nitrote (AgNO3). Useboth models to show whot hoppens whensodium chlor ide ond si lver ni l rote reoct ino replocement reoction.

I t .

12.

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hos: 13 .

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I

$sttindPoinf 8$

V'

fr

v

Y

W o"o* Conclusions14. Reod the possoge. Then drow o

conclusion bosed on the focrs.

Mony moteriols hove been creotedby chemists. Silk wos expensive, sochemists worked to moke o fobric toreploce it. Plostics ore inexpensivecompored with metols ond othermoteriols thot plostics hove reploced.

Moke o grophic orgonizer l ike this one.Put the focts ond conclusion into yourgrophic orgonizer.

Foct

ffi-Focl

Choose f he lelter thof best completes thestotemenl or onswers the quesf ion.

15. Which is on exomple of o chemicolchonge?@ woter f reezing in o puddle@ o dry sponge exponding ofter being

put in dishwoter@ food being digested in the smoll

infesfine@ butter melting in o microwove oven

ftrt"rf Prep

| ó. Whot kind of reoction occurs when woferbreoks down, producing hydrogen ondoxygen goses?

@ o combinot ion reoct ion@ o decomposition reoction@ o recombinof ion reoction@ o replocement reoction

| 7. Which moler iol d id chemisls moke inthe lob?@ cotlon@ wool@ s i l k@ nylon

18. I f you ore going to use o cleoning productyou've never used before, whot shouldyou do first?@ Open the window.@ Put on cover goggles.@ Reod the direclions.O Put on gloves.

| 9. Exploin why f he onswer you chose forQuestion I B is best. For eoch of theonswers you did not choose, give oreoson why if is not lhe best choice.

. .rr. @!G rrqrrqflYr rYruKe: o t ¡ r * l i * .how¡nq four moin th inos

you've done so for todoy. Then writeo norrotive telling how eoch of theseoctions involved one or more chemicolreoct ions or chemicol tech nolog ies.

Conclusion

t

399

If you ore olwoys wondering whot fhings ¡¡re mqdeof, you moy enjoy q cqreer in mqferiqls science.

As o moteriqls scientist, your job would be to studythe otomic or moleculor structure of different moteriols.Mony moteriols scientists work moinly with metols. Othersconcentrote on olostics. Some work with semiconductors-moteriols importont in computers. Sti l l others combine o vorietyof moteriols for different uses.

Moteriols scientists design new moteriols. They test how wellthe moteriols work in different producfs. Sometimes they figureout the best woys to monufocture the moteriols. Moteriolsscientists often work in o lob. They need good moth ondscience skil ls. They usuolly work with o teom. Therefore,they need to be oble to communicotewell foceJoJoce. They olso need ioreport obout their work, so theymust know how to write well.

For this coreer, you wil l need odegree in physics, chemistry, orengineering. Even ofter you hove o job,you wil l need to continue your educotion.This will help you keep leorning obout thenew moteriols thot ore olwoys being produced.

Identify different moteriols in objectsin ond oround vour home. Moke o chortthot lists the moteriols ond the tvpes ofobjects eoch is used for. In o third column,l ist chemicol ond physicol propert ies youthink moke eoch moteriol good for its uses. l

motion of o pendulum?

goggres

i' _ -, '. \'.

- , - i , . . : - ' '

ond stringt"- -'

Moferiols

sofety

&wosher

ffir{"'mosking tope

ond meterstick

C-

mer or stopwotch

r- \You observewhen you use yoursenses lo gotherinformolion.You infur whenyou moke ojudgmenl bosedon observotionsor exper¡ences.You predicl whenyou moKe oninference obout ofulure result. Youexploin when youclorify the reosonssomething is thewoy it is.

Explore How con you leorn obout the

Whor lo Do

Moke o pendulum.

Pull bock the pendulum 30 cm.Let go. Observe how the speedchonges during o swing.

Whene does the woshen rnove fostesf? slowesf?Whene does if speed op? slow down?

Test ogoin from 30 cm bock.T ime 5 swings.

A "swing" is one bock-ond-fonfhrnovemenf.

Predict how pulling bock thependulum ó0 cm would offectthe time needed for 5 swings.Test your prediction.Time 5 swings.

Weon sofetggoggles.

The downwond poll ofEonfh's gnovitg sfontsthe pendulurn moving.

2.

;

Pollbockondleig.. <-m

Exploin Your Resultst . Compore the time needed for,30cm ond ó0cm

swings. Infer how the disionce o pendulumswings offects the time o swing tokes.

Predicr Suppose the string wos shortened.How do you think this would offect the timeo swing iokes? Exploin.

loko lt to lht Notp€orso¡succossnel.@m

''@co,rre qnd Effect

Understonding cquses qnd effects con help you understondwhot you reod. A couse moy hove more thon one effect. Aneffect moy hove more thon one couse.

r Sometimes on effect wil l be the couse of onother effect.

¡ Sometimes you hove to infer the couse or effect from theinf ormotion given.

Possoge from o Sf,ory

Sondy pushed Somuel on the swing. Eoch push

mode Somuel go higher. Becouse of this, Somuelbecome ofroid. So, Sandy stopped pushing. Sincehe wosn't being pushed onymore, Somuel slowlycome to o stoD. But he wos still ofroid.

Apply It!Moke grophic orgonizerslike the ones shown. UnderCouses, write on ociion

Couses

Sondy pushed

Effecls

Somuelwenthigher.

thot hoppened in the story.Under Effects. write whothoppens os o result of thecouse. In this story, eocheffect becomes o cousefor onother effect. Thegrophic orgonizers orestorted for vou.

Somuel wenlhigher.

262 kilometers per hour. You left Son Diego this morning oteleven o'clock, ond you'll be in Los Angeles before noon. Didyou know o troin could move thot fost?

lesson I

How can youdescribe motion?

Seo sl,ors oreonimols thotmove veryslowly.

. Leaves wave and dance in the wind. A ball bounces back

and forth from one child to another. A bird flies right, Ieft, up,

and down. You can describe motion in manv wavs.

Types of MotionYou 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. Yourheort beots ond your eyelids blink up ond down.

Motion is oll oround you. Objects move in mony different

woys. Whot kinds of motion hove you seen in 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 need o high-speed comero

;. 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 buses hove'icble motion-they move in mony directions

end ot mony speeds. A pendulum has periodicotion-it swings bock ond forth. Wheels

move in a circular motion. A rubber bond hosvibrational motion when you pluck it. How

d you demonstrote eoch of these motions?

I ú9¡Cgl.eqint.t Whot ore three lypes of molion?

2 E@Ñ&@DescriptiveWriteoporogroph in your sciencejourncl describinglhe motions you hove enjoyed on ploygroundequipmenl. Write your porogroph in the style of omogozine orlicle. Use the heodline "The Best Rideon the Ployground."

Speed ond VelocityAveroge speed describes how for on obiect moves during

o certoin omount of time. To colculote overoge speed, use thefollowing formulo:

Averoge Speed - DistonceTime

I

?

,t

ú

ú

I

J

If o cor movedwould be:

1O0 meters in 20 seconds, its overoge speed

100 m -5720s

When you sit os still os you con, ore you moving? Do notbe too quick to soy^you ore not moving. In relotionship with

your choi4, you moy be sitting still. Inrelotionship with the Sun, you ore movingvery quickly. You ond the planet you oresitting on ore moving around the Sunfoster thon ony rocket. So, the motionof on obiect connot be meosured by iustlooking ot the oblect. Motion is olwoysmeosured in relotionship with somelocotion colled o point of reference.

The speed ot which a person is movingcon vory occording to which point of reference you use. Forexomple, o possenger wolking down the oisle of o troin is inmotion. But the possenger's motion meosured in relotionshipwith the end of the troin cor is different thon the possenger'smotion relotive to o crossing gote olong the trocks.

F

Y

b

Using the end of the troin cor os o point of reference, thepossenger wolking 10 meters down the oisle in 5 secondswill hove o wolking speed of 2 meters per second. But usingthe crossing gote neor the trocks os o point of reference, thepossenger is moving obout os fost os the troin-perhops30 meters per second.

Speed ond velocity ore not the some. Veloci$ describes thespeed ond the direction of on obiect's motion. The speed ofthe troin might be described os 30 meters per second, but itsvelocity is 3O meters per second north. A folling skydiver mighthove o velocity of obout 200 kilometers per hour down.

¡! tesson Checkpoint ,

l. Robert moved 28 meters in 4 seconds. Tollono moved ó00 metersin 2 minutes. Jovier moved 40 melers in 5 seconds. Lisl fhesepeople ond their speeds in order from foslest to slowesl.

2. Whot do you need to know to find on object's velocily?

3 U@@ ExposiroryWrite o porogroph in yoursciencejournol thot exploins how circulor motion ond vorioblemotion ore ol ike ond dif ferenl.

This hoin is moving ot o' h¡gh speed from the point of

reference of the crossing gofe.

b

b

l o m ^ m5 s - ' s

!!-Q..1tr - en[5 s

- w " sSignol Light

An opple folls to theground becouse theforce of grovity pullsit üowqrd Eorth's cenler.

Groüty couses fhevelocity of the opplelo increose os it folls.

After one second offolling, on opple'svelocity will be oboutl0 S downword.

After two seconds offolling, on opple'svelocity will be obout20 f downword.

lesson 2

What are forces?There are many kinds of pushes and pulls around you.

These pushes and pulls can cause objects to change theirvelocities.

Pushes ond PullsA force is o push or pull thot octs on on obiect. When

one obiect pushes or pulls onother oblect, the first obiectis exerting o force on the second one. Forces con moke omoving obiect speed up, slow down, or chonge direction.

Forces hove both mognitude ond direction. Themognitude of o force is how strong the force is.Mognitude is meqsured in units colled newtons (N). Thedirection of o force con be described by telling whichwoy the force is octing. For exomple, o medium-sizedopple held in your outstreched hond exerts o downwordforce with o mognitude of obout 1 newton.

GrovityEvery obiect in the universe exerts o grovitotionol pull

on every other obiect. But only the grovity of o lorgeobiect such os Eorth is strong enough to be felt. Eorth'sgrovity pulls other obiects toword its center withoutever touching them. Pendulums swing, opples foll, ondortiflciol sotellites stoy in orbit becouse of Eorth's grovity.

An obiect's weight is the omount of grovitotiono-force between it ond Eorth. This force depends on theobject's moss ond Eorth's moss. It olso depends onEorth's size ond how for gbove Eorth the obiect is. Ifyou fly in on oirliner, your weight is o little less. If ypuwent to onother plonet, your weight would olso chonge.The toble on the next poge shows how much on objectwould weigh on some other plonets if its weight on Eorthis 100 newtons.

ra

410

1 . fTCnectpoint. Whot ore lwo exomples thot'

i l lustrote Eorfh 's grovi tot ionol pul l?t Z O C<¡use ond Effecr A rock tumbles down

o hill.Identify the couse ond effect of this event.

Mognefism ond ElectricityMognetism is o force thot pushes ond pulls on other obiects.

The mognetic force is greotest ot o mognet's poles. The polesofo horseshoe mognet ore ot the two ends. The poles ofo bormognet ore ot either end. Every mognet hos o north p.ole ondo south pole.

Mognets will strongly pull on objects mode of iron, cobolt,nickel, ond godotrinium. Mognets will olso exert forces on othermognets. The north pole of one mognet will ottroct the southpole of onother mognet. The north poles of two mognets willpush owoy from eoch other. The south poles of two mognetswill oct in the some woy.

Electric forces oct between obiects thot oreelectricolly chorged. Obiects get electricolly chorgedwhen they goin or lose electrons. Remember thotoll otoms hove negotive electrons ond positiveprotons. If on obiect goins electrons, the obiect willbe negotively chorged. If the oblect loses electrons,it will be positively chorged. Why would on objectget o positive chorge if it loses electrons?

Electrons often move from one obiect toonother 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 chorgefrom your hoir.

A mognel exertsmognetic force thotpulls pieces of irontoword it.

A negotively chorgedcomb will ottroctpoper becouse ofeleciricol forces.

I

J}n¡,, I

rtr1

NT

AII objects thot ore electricolly chorged willexert forces on eoch other. Oppositely chorgedobjects ore ottrocted to eoch other. Obiectswith the some chorge ore repelled, ond moy.move owoy from eoch other.

Grovity, Electricity, ond MognetismLike grovity, mognetic qnd electric forces con oct

between objects even if the obiects do not touch. Allthree forces increose os obiects get closer together.Grovity, electricity, ond mognetism hove differences.The forces of mognetism ond electricity behveenobiects con be blocked by putting certqin kindsof moteriols between the obiects. Grovity con't beblocked. Electricity ond mognetism con push or pullon different oblects. Grovity exerts only o pullingforce on obiects.

Mognelic forces couse thisexperimenüol troin lo floqtobove the trock. Mogneticforces ore olso used lomoke the Foin move olongthe trock ot very highspeeds.

The mognetic field of thisstone otlrocts metol pinslo its suloce.

L t&Cnecfpoint. Whol ore the couses of electricond mognetic forces?

2. '@

Cause ond Effect Describe on eventinvolving eleclric ond mognetic forces. Use yourimoginotion. Describe the couse ond effect ofeoch force.

l- -.u

FrictionHove you ever slid ocross o smooth floor with

your socks on? You con't slide os eosily if youore weoring your shoes. Friction is ot work.Friction is the force thot results when twomoteriols rub ogoinst eoch other.

Friction octs to slow down the motion of onobject or keep it from storting to move. Unlikeother forces, friction depends on quolities of theobjects involved. The shope, speed, or texture ofone object con offect the omount of friction withonother obiect. The texture of the soles of yourshoes is different from the texture of your socks.Friction is greoter between your shoes ond thefloor thon beftveen your socks ond the floor.

r

The shope of shorksond their speciol skinreduce friction withhe woler ond ollowthe shorks to swimsmoothly ond swiftly.

Speciol pods on obicycle's brokes pushogoinst the tires. fhisresults in increosedfriction thot slows downor stops the bicycle.

A bicycle hos mony feoturesthot increose friction. Otherfuotures, like boll beorings,decreose friction. Bothmoke the bike soferond eosier io ride.

414

Air ond woter resist motion when o movingobiect 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. Mostcors ond oirplanes ore designed to hove little oirfriction. Submorines ond ships ore designed with

shopes to help them move through woter.

1. J, . How does f riction offect movement?

2. The orovitotionol force on the Moonis one-sixth of whot it is on Eorfh. This meons thot on theMoon you would weigh one-sixth of whot you weigh onEorth. How much would you weigh on f he Moon?

On some bicycles the: low hondlebors ollow'the rider to bend downond decreose oir friction.

The texture of the foom onthe hondlebor increosesfriction between the rider'shonds ond the hondlebors,moking it eosier io hove ofirm grip.

The rough treodon this bicycle tireincreoses the friciionbetween the tire ondthe ground. Thiskeeps the bicyclefrom sliding duringlurns.

The distonce it tokesüo stop o skidding cordepends on lhe surfoce ofthe rood.

0 50 100 150

Stopping Distoñce {ml lrom 45 km per h

o

4L5

Work qnd PowerYou heor the word "work" used oll the

time. But the scientific definition of work hoso porticulor meoning. I/Vork is done wheno force moves on object. To colculote work,you multiply the force (in newtons) octing onon obiect by the distonce the force couses theobiect to move.

Force x Distonce : Work

Work is meosured in joules.One ioule (f) is the omount of workdone when o force of 1 newton (N)moves on obiect o distonce of 1 meter (m).

If the force opplied to on objectdoes not moke the obiect move,then no work hos been done. Work isdone only when the obiect moves otIeost portly in the some direction inwhich the force is opplied. Holdingon object in ploce con require o force,but since the obiect does not move,no work is done.

Work is donewhen o forcemoves on object.

4

Force Disfronce Work

10N 0m l0Nx0m:0J

lr

b'

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

Work - PowerTime

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

No work is being donewhen on object is heldwithout moving, no motierhow long the object is held.

¡f L"""on Checkpoint;

b

I

,

t

t .')

3.

Whof ore two exomples of forces?

Whol kind of force con moke poper cling lo o comb?

Find picfures thot show howthe shopes of cors hove chonged over time. Describefeotures on modern cors thof help reduce oir friction.

Work Time Power

20J / l - H:,*40J 4s fl: row

20J 20J _2s t0w

4t7

lesson 3

What areNewton'slaws of motion?

A ball rolls faster and faster as it travels downa hill. Finally it bumps into a tree and stops.Newton's laws of motion explaín why objectsIike the ball move the way they do.

Net ForcesDifferent forces con oct on on

obiect ot the some time. They moyoct in different directions, ond somemoy be stronger thon others. Thecombinotion of oll these forces is thenet force on the obiect. The net forcedetermines whether the obiect willstort moving, stop moving, orchonoe direction.

If o stonding box is pushedin one direction by morelhon one force, the net forceis lhe sum of the forces.

418

An oirplone moves in o stroight line ot o constront speed. Itspeeds up, slows down, or chonges direction depending on

e net forces octing on it.

It

Drog is o force thotpushes ogoinst theforword mofion of on

When equol forces oct on on obiect in opposite direcüons,the forces ore bolonced. Then the net force is zero. Boloncedforces do not chonge the woy on obiect moves.

An obiect is in o stote of equilibrium when oll theforces octing on it bolonce eoch other. A stonding oblect inequilibrium will remoin motionless. A moving obiect inequilibrium will continue to move ot o constont speed ino stroight line.

If the forces octing in one direction ore greoter thonthe others, the forces ore unbolonced. Unbolonced forcesocting on on obiect couse it to chonge its motion. The netforce is found by combining oll the different forces octingon on obiect. For exomple, if two people ore pushing on oIorge box from opposite directions using the some omountof force, the box does not move. But if one person pusheshorder thon the other, o net force results ond the box moves.

I Sg!fe,.l1pgig_.,; How con on object be mofionless ondin eoui l ibr ium?

2. @Couse cnd Effect How con the forces in o gome oflugof-wor result in equilibrium?

Thrust pushes onoirplone forword,moking it occelerole.

zero N

If o sionding box ispushed in oppositedirections by equolforces, the forces orebolonced. There isno nel force, ond lhebox does nol move.

If o box is pushed inopposiie directionsby unequol forces,the forces oreunbolonced. Thereis o net force inthe direction of thestronger force, ondlhe box moves inthot direction.

oirplone, slowing it

4L9

Nerrlon's First LqwNewton's first lqw of motion soys thot

unless o net force octs on on object, theobiect will remoin in constont motion. Anobiect ot rest stoys ot rest until o net forceocts on it. An obiect moving ot o constont

speed will continue to move in o stroightline ond ot o constont speed.

The tendenry of on obiect to resist onychonge in motion is known os inertio.Objects with o lot of moss hove moreinertio thon obiects with Iess moss. The

body's inertio is whot forces you ogoinstthe side of o cor when it turns. When o corchonges direction, your body tends to keepmoving stroight. The cor is pushing on you

during o turn. Inertio is olso whot mokesyour body rise up from your seot in o rollercooster os it goes up ond over o steep hill.At the top of the hill, your body tends tocontinue going up when the ride moves

down the hill.Spoce probes ore olso exomples of

Newton's first low ond inertio. Inertio keepsthe probes moving through spoce. As oresult, probes need very little fueI ofter theyore lounched. They usuolly use fuel only tochonqe direction or to slow down.

Inertio hos ollowed thespoce probe Voyoger totrovel oll the woy out ofthe solor system whileusing very little fuel.

¡ ¿ "q

420

Alhough the force of the kickis opplied for only o shorltime, ineriio will couse thefootboll to continue to movethrough the oir ofter *re kick.

A full truck hosmore inertio thonon empty huck,ond it will tokemore effort tomqke it eitherspeed up or stop.

t .

A seot belt prevents thetest dummy's inerliofrom corrying the dummythrough the windshield.

-y'7Gheckpoint.. Whot is inertio? How does it offectthe wov on obiect moves?

Use photogrophs from mogozines tocreote o colloge obout Newfon's first low of motion.Try to find os mony exomples os possible thot illustrolethinqs thot ore in constont mot ion or ot constont rest .

421

Nevvlon's Second LqwNewton's second low of motion describes how

occelerotion, moss, ond net force ore reloted.

Accelerotion is the rote ot which the velocity

of on object chonges over 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 chonges conbe colled occelerotions.

The formulo thot describes the relotionshipbetween force. moss. ond occelerotion is:

Force = Moss x Accelerotion

The formulo is often written os F : m x o.It indlcotes thot the stronger the force octingon on object, the more thot obiect will occelerote.

The formulo olso indicotes thot o forcewili couse on obiect with smoll moss tooccelerote more thon on object with

lorge moss. The occelerotion due to osmoll force on o smoll obiect con bethe some os the occelerotion of obig force on o big obiect.

The net force octingon the box is equolto the moss of thebox multiplied byits occelerotion.

The troin engines musl exerienough force io pull thefreight cors behind them.The more freight cors thereore, the more force theengines must exeri.

Force Moss Accelerotion

200 N 100 ks . m¿ ; í

Newton's Third LowNewton'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 ofmotion. 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 onequol ond opposite force. It is actuolly impossible tohove one force without on equol ond opposite force!

For exomple, o person who leons ogoinst o wollexerts o force on the wall. The woll exerts on equolforce on the person in the opposite direction.

If you hove ever ridden bumper cors, you knowthot when o moving cor collides with o stopped cor,

both drivers feel the force of the collision. The driverof 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.

Both morbleschonge velocitybecouse of lheforces.

¿

Fl

The person pushes on thewoll. The woll pushes onthe person. Forces of thewoll ond person ore equolond opposite.

When the morblescollide, they will exertforces on eoch other.

The red morble exertso force on the bluemorble. This couses fheblue morble tro chongeits velocity.

The blue morble exerlson equol but opposileforce on the redmorble. This cousesthe red morble io olsochonge its velocity,

{

r , '

Although the force of the kickis opplied for only o shorttime, inertio will couse thefootboll ¡o continue lo movethrough the oir o{ter the kick.

A full truck hosmore inertio fhonon empty truck,ond it will tokemore effort lomoke it eiñerspeed up or slop.

A seot belt prevents thetest dumm/s inertiofrom corrying the dummythrough the windshield.

I . ,y'7 Checkpoint- . Whol is inertio? How does it offectthe woy on object moves?

2. UMGG} use photogrophs from mogozines tocreote o col loge obout Newton's f i rst low of mot ion.Try to f ¡nd os mony exomples os possible thol i l lustrotethings thot ore in consfont mot ion or of constont rest .

42L

NeurJon's Second LqwNewton's second low of motion describes how

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 chonges conbe colled occelerotions.

The formulo thot describes the relotionship

between force. moss, ond occelerotion is:

Force : Moss x Accelerotion

The formulo is often written os F : m x o.It indicotes thot the stronger the force octingon on obiect, the more thot object will occelerote.

The formulo olso indicotes thot o forcewill couse on object with smoll moss tooccele¡ote more thon on object withIorge moss. The occelerotion due to osmoll force on o smoll obiect con bethe some os the occelerotion of obig force on o big object.

The net force octingon the box is equoltro the moss of ihebox multiplied byits occelerqtion.

The troin engines must exertenough force to pull thefreight cors behind them.The more freight cors thereore, the more force theengines must exeri.

r

Force Mqss Accelerotion

200 N 100 ks

?

There ore different ways to write the formulofor the second low of motion. The formulo youuse depends on whot question you ore trying toonswer. If you want to find the occelerotion ofon object thot hos o force on it, you con use thefollowing formulo.

Fv - m

If you wont to find the moss of on object thothos o force on it, vou con use the formulo below.

b'

Fm=; .

To slow down more quickly,o roce cor needs io hove obig force. With o porochute,the force of qir friction isincreosed ond the cor slowsdown more quickly.

The greotrer lhe mossof o box, the less theoccelerotion will be.

b

l. .!0Cnec*point; Use Newton's second lowof motion fo exploin whot hoppens whensomeone pushes o choir ocross the floor.

Whot formulowould you use lo find the occelerotionof o l0 kg boulder being pushed by oforce of ó5 N? Whot would theoccelerotion be?

The. greobr the netforce pushing onthe bo:q fhe greolerthe occelerotion ofthe box.

: : i i &

Force Mqss Accelerotion

400 N 200 ks ^ m¿g

423

Newlon's Third LowNewton's third low of motion stotes thot when

one obiect exerts o force on o second object, thesecond obiect exerts o force on the first obiect.This is sometimes colled the oction-reoction low ofmotion. Action-reoction forces ore olwoys equol ondopposite, 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 onequol ond opposite force. It is octuolly impossible tohove one force without on equol ond opposite forcer

For exomple, o person who leons ogoinst o wollexerts o force on the woll. Ihe woll exerts on equolforce on the person in the opposite direction.

If you hove ever ridden bumper cars, you knowthot when o moving cor collides with o stopped cor,

both drivers feel the force of the collision. Ihe driverof the stopped cor feels o force ond storts to move.The driver of the moving cor feels on opposite forcethot slows the movino cor.

Both morbleschonge velocitybecouse of theforces,

I

.ltC

lt

¿

The person pushes on thewoll. The woll pushes onlhe person. Forces of thewoll ond person ore equolond opposite.

When the morblescollide, they will exerrforces on eoch other.

The red morble exertso force on the bluemorble. This couses lheblue morble to chongeits velocity.

The blue morble exertson equol but oppositeforce on the redmorble. This cousesúe red morble tro olsochonge ifs velocity.

{

424

$q ñ k

2:5

I

;

l . Wh¡ch of Newton's lows of mot ion is demonstroted by o hommer poundingo noi l into o boord?

2. A sotellite orbiting Eorth is knocked out of orbit by o meteor. How conNewton's lows of motion be used ¡n describing this event?

3. '@

Couse ond Effect Whot w¡ll be the effect of two people pullingon o box wilh lhe some omount of force buf in oooosite directions?

Lesson 4

What aresimplemachines?

Simple machines make work easier. Every time you usea hammer, a screwdriver, or a doorknob, or walk up aramp, you are using a simple machine to do work.

Mqchines ond WorkRemember thot work is done when o force

couses on obiect to move. Some obiects orelorge, heovy, or owkword to move. A mqchineis o device thot chonges the direction or theomount of force needed to do work. Simplemochines ore mochines with only o few ports.There ore severol kinds of simple mochines,including o wheel ond oxle, pulley, inclinedplone, ond lever.

Mochines do not reduce the omount of workthot needs to be done. They con moke it eosierto do the work. When o mochine ollows you touse o smoller force to do work, you must opplythot force for o greoter distqnce. In this woy,the totol omount of work stoys the some.

PulleyA pulley is one type of simple mochine. A pulley

consists of o rope or coble thot runs through ogiooved wheel. A simple pulley mokes work eosierby chonging the direction of the force needed todo work. Flagpoles ond dropery rods use pulleys.A block ond tockle is o system of pulleys thot mokeit eosier to lift very heovy oblects.

This pulley does notchonge lhe omount ofwork done. fhe moss ofthe box pulls down onthe pulley with o force ofl0 newlrons. The personmust pull on the pulleyrope wi$ fie some force.Notice thot if the rope onthis pulley is pulled downI mefrer, the box is liftedup I mel,er,

426

!a

Lesson 4

What aresimplemachines?

Simple machines make work easier. Every time you usea hammer, a screwdriver, or a doorknob, or walk up aramp, you are using a simple machine to do work.

Mqchines ond WorkRemember thot work is done when a force

couses on obiect to move. Some obiects orelorge, heovy, or owkword to move. A mochineis o device thot changes the direction or theomount of force needed to do work. Simplemochines ore mochines with only o few ports.There ore severol kinds of simple machines,including o wheel ond oxle, pulley, inclinedplone, ond lever.

Mochines do not reduce the omount of workthot needs to be done. They con moke it eosierto do the work. When o mochine ollows you touse o smoller force to do work, you must opplythot force for o greoter distonce. In this woy,the totol qmount of work stoys the some.

PulleyA pulley is one type of simple mochine. A pulley

consists of o rope or coble thot runs through ogiooved wheel. A simple pulley mokes work eosierby chonging the direction ofthe force needed todo work. Flogpoles ond dropery rods use pulleys.A block ond tockle is o system of pulleys thot mokeit eosier to lift very heovy oblects.

This pulley does notchonge the omounl ofwork done. fhe moss ofthe box pulls down onthe pulley wiih o force ofl0 newlrons, The personmust pull on the pulleyrope with the some force.Notice thoi if the rope onthis pulley is pulled downI mefer, the box is liftedup I meler.

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Wheel ond AxleA 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 theomount 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 ore two exomples of o wheelond oxle thot con moke work eosier?

2 E!EÑE@@ Usethelnternetorolibrory to find the eorliesl recorded uses of simplemochines. Write I or 2 porogrophs in your sciencejourncl on your findings.; l ¡ t !

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Boll beorings ore steelbolls used inside owheel to reduce frictionond moke o pulley orwheel ond oxle moreeff icient. The beoringsore greosed to helpthem furn more eosily.

on the wellis o kind of wheel ondoxle thot reduces theforce needed io roise lhebucket Your honds opplyo force for 90 cm whileroising the buckei onlyl0 cm. You ore opplyingless force lhon you wouldif you lifted sroighi up onthe rope. But you opplyfie force over o greolrer.distonce.

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The pulley shown frhere mokes W.work eosier. less ?1force needs io be froppf ied over o 7ú 1 ̂longer disüonce.Only 5 newtonswill be needed tolift the lO-newfonbox. Notice úotif the rope on úispulley is pulledI meler, the boxis lifted only0.5 meler.

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LeverA lever is o type of simple mochine

in which o stiff bor rototes oround ofixed point colled o fulcrum. Leversdo work by using the stiff bor, thefulcrum, o lood, ond o force you opply.

A lever such os o see-sow chongesthe direction of o foice. When o person

uses o see-sow to lift o box, the personpushes down, but the box goes up. Asthe position of the fulcrum chonges,the omount of force needed to movethe box will chonge. The forther thefulcrum is from the person using thelever, the eosier the lever is to use.

Above ond to the right is o pictureof o person lifting o box with o lever.The force thot the person must opplyis less thon the weight of the box. Thismokes the work eqsier. Also notice thotolthough the needed force is less, theperson must opply this force for 1 mwhile the box goes up only 0.5 m.

OtherSimpleLevers

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A lever chonges thedirection of o force.

Mony everydoy itemshove levers. How dothe ports of these itemshelp people do work?

LeverA lever is o type of simple mochine

in which o stiff bor rototes oround ofixed point colled o fulcrum. Leversdo work by using the stiff bor, thefulcrum, o lood, ond o force you opply.

A lever such os o see-sow chongesthe direction of o foice. When q person

uses o see-sow to lift o box, the personpushes down, but the box goes up. Asthe position of the fulcrum chonges,the omount of force needed to movethe box will chonge. The forther thefulcrum is from the person using theIever, the eosier the lever is to use.

Above ond to the right is o pictureof o person lifting o box with o lever.The force thot the person must opplyis less thon the weight of the box. Thismokes the work eosier. Also notice thotolthough the needed force is less, theperson must opply this force for 1 mwhile the box goes up only 0.5 m.

OrherSimpleLevers

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A lever chonges ihedirection of o force.

Mony everydoy itemshove levers. How dothe ports of these itemshelp people do work?

Inclined PlonesHove you ever tried corrying o heovy lood up o

flight of stoirs? It's much eosier to roll it up o romp!An inclined plone is onother type of simple mochine.It consists of o flot surfoce with one end higher thonthe other. The inclined plone con be o romp lorgeenough for o person or o vehicle to use, or it con bevery smoll.

The distonce from the floor stroight upto the plotform is less thon fie dislonceused with the inclined plone. But moreforce must be opplied io lifi thebox directly from the flooronlo the plotform.

Pushing o box up on inclined plone f,o o plotform ismuch eosier ihon lifting fie box. Using the inclinedplone covers more disionce, but o smoller omountof force is used.

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Whot ore the ports of o lever?

Mony joints in your body workl ike simple mochines. Your knee ond elbow joints orel ike levers. Think of two oct iv i t ies ¡n which the knees orelbows oct os levers to do work. Where is lhe fulcrum ineoch octivitv?

If you push o wheelchoir up oromp, you would use less forceover o longer distonce thon ifyou were to lift the wheelchoirto the some height.

Other InclinedPlones

A screw is o smoofi melolrod with o tiny inclinedplone wropped oroundit. Screws con be used topull two pieces of woodtogether ond hold them inploce, Screws con olso beused in jocks thot lift cors.

A rubber doorstop is osmoll wedge thot is used tokeep o door from moving.This doorstrop is o wedgethot consists of one inclinedplone ond one flot plone,Some wedges, such oson oxe, ore mode of twoinclined plones ploced bockto bock. This creotres omochine thot con be usedto split wood.

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Complex MochinesA mochine thot uses two or more simple

mochines is colled o complex mochine. Monycomplex mochines use electricity, grovity, burningfuel, humon force, or mognetism to operote eochof the simple mochines within it. This go cort ison exomple of o complex mochine.

The sieering wheelis port of o wheelond oxle thot mokesit eosier tro turn the90 corl.

axle

This crone is ocomplex mochine.Whot simplemochines con yousee in lhe crone?

wheel

The wheel ondoxle of the steeringwheel move leversthot turn the frontwheel.

The pedols orelevers. The driver's

or brokes.

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Soiling ships ore complex mochines. They hovemony ports thot work together to moke the shipmove properly. Pulleys ore used to lift the soils intoploce. The rudder is o lever. A wheel ond oxle moy beused to move the rudder. A wheel ond oxle moy olso

be used to lift the heovy onchor. Some soiling shipsused oors to help move the ship. Oors ore levers.

By.itself, ihe engine oflhe go cort is o complexmochine mode up ofmony simple mochines.

Soilboots ore complexmochines fiot iurn windenergy inlro kinetic energy.Brokes conioin levers.

One end of the leveris pulled by o coble,cousing the oiher endto press ogoinst o diskthot is ottoched to thewheel.

The engine is notconnecbd direcdytro úe tires. Thegeors ore osystem of wheelsond oxles.

.S tesson Checkpoint,

I . Why is o screw considered o simple mochine?

2. Nome one complex mochine ond two of the simple mochinesthot moke it uo.

3. @ Couse ond Effect When you use o screwdriver loopen the lid of o point con, lhe couse is the force you opplyto the screwdriver ond the effecf is the lid coming off . Describethe couse ond effect of using some other simple mochine.

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Investigqte How con youdescribe motion?When soccer ployers kick o boll, they esl¡mqte how it will move.When scientists invesligofe motion they meosure. In this octivifyyou find how the speed ond direction of o boll chonge os it movesolong, hi ts o wol l , ond bounces off ot on ongle.

Whor to DoMqteriqls

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mosking tope

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¡ ¡ t :r*_fjfla\ @-P:;+i" r l . : : , : r 1 - , : i

prolrocror

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" '-..meterstick ")

Mork on impoct spot with tope ot the boseof o woll. Put o protroclor ot the impoctspot. At on ongle ó0' out from the woll,meqsure o poth 4 meters long ond morkit with tope. At the poth's outer end, writeSiorting Line.

At on ongle l20o out f rom the wol l ,meosure o poth 4 meters long ond mork itwith tope. At the poth's outer endwrile Endíng Line.

From obout 'l

meier behind the Stortingline, gently push the boll so it rol ls olongthe poth. Stort the t imer when the boll iposses fhe SÍorÍing line (Time 1). .Recordthe time the boll hits the impoct spot(Time 2). Stop ihe timer when the bollcrosses the Ending Line (Time 3).

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tJtimer or stopwolch

meo'ure us¡ngstondord un ifs,such os meters, ornonstondord unitssuch os lhe lengthof o poper c l ip.

Y@ Oroph the distonce the boll trovels ond the time it tokes. Impocf Spof

Recond the tine.

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Design ond consfn¿lcf o dofo loble ond o gnoph.Yoo con seleci fhe ones shown on design goon own.A foble ond gnoph will help goo ongonize, displog.onolgze, ond exploin goon dofo ond gortn findings.

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d"*'í"-'f "'.3---?*-í-*¿"*'7" " s'Time (seconds)

Yoon feochen nighf osk gou fo ctse gnoph popen.

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Exploin Your Resultsl . Using your meqsuremenfs, f ind the boll 's

speed from the Storting Line to the ImpoctSpot. Find the speed from the Impoct Spotto the Ending Line.

speed=disfonce+f i rne

Infer Did the boll move ot o steody speed?Exploin your onswer.

2.

How would your grophbe different if you showedyour resuhs in feet insteodof meters? Find out. Write oreport of your results in yourscience journol.

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You hqve leqrned thqf fhe mqssof ony moller is fhe sqme onfhe Eorfh or in spoce. Weight,however, depends on fhe forceof grovity.

The grovitotionol force on the Moonis i of the grovitotionol force on Eorth.How much would o

' l 8O-oound ostronout

weigh on the Moon?

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An ostronout who weighs 1 80 poundson Eorth would weigh only 30 pounds onthe Moon.

You hove leorned thot powerdescribes how fqst work is done.

How much power is needed to complete150 joules of work in 40 seconds?Remember, power is meosured in wotts.

^ worklOWe[ = - .

f lmer50= ,lo

= 39 or 3.25

The oower needed is or 3.25 wotts.

Answer eoch ouestion.' l . An Apollo ostronout's l i fe support

system wos o bockpock thot hod ototol weight of obout ó8 pounds onEorth. About how mony pounds didthe bockpock weigh on the Moon?

2. How mony joules of work ore donewhen o force of 2 newrons moveson object 2.5 meters?Remember, Work = force x distonce.

3. How much oower is neededto complete 21 0 joules ofwork in ó0 seconds?

Use the librorv or the Internet to find moreinformolion oboul the Eorth weight of itemsthe Apollo ostronouts wore or corried whenthey wolked on the Moon. Find the weightof eoch item on the Moon.

Use Vocqbulory i Exploin Conceptsoccelerolion mochine $. a26llp .4221 power (p. 417)equilibrium{r];i¡

- velocitY (P aoe)

force (p.410) work (P' 4]ó)

inertio (p. 420)

Use lhe vocobulory word f rom the lisl obovethot best compleles eoch sentence.

I. An object resists o chonge in molionbecouse of

2. A - is o device lhot mores worreosier to do.

3. The - of o moving object describesits speed ond direction.

4. When oll forces octing on on objectbolonce eoch other, lhe object is soidto be in o stole of

5. Grovily is o - thot pulls objectstoword the cenler of fhe Eorth.

is done when o force moves onobject.

rs Tne roTe oT wntcn vetoctry

is the rote ot which work is done.

Exploin why on object in o stote ofequi l ibr ium could be either in motionor stonding st i l l .

Exploin how you con use o simplemochine lo moke o job eosier.

Predict whot would hoppen to o roflf loof ing on o loke if o swimmer dives intothe woter from one end of the roft.

Observe Compore ond controsl o pulleyond o wheel ond oxle.

Cquse qnd Effect| 3. Moke o grophic orgonizer like fhe one

shown below. Under the word Effecl, useNewton's second low of motion to exoloinwhot wi l l hoppen.

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One ice skoteris skofingforword. Asecond skotercomes frombehind ondgent¡y pushesthe firsl skoter.

Effect

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Rt"rt PrepChoose the letter thot best completes theslolement or onswers the question.

| 4. Sotellites ore held in orbit oround Eo¡hbecouse of@ the Sun's groyity.@ thrust from the sotellite.@ Eofh's grovity.@ drog f rom the sotellite.

| 5. Which of the following stotements is f rueobout horseshoe mognets?@ The mognetic force is strongest in the

middle of the mognel.@ The mognetic force is weokest ot the

lwo ends.@ There is one pole ot the middle of the

mogner.@ The mognetic force is strongest ot the

two poles.

| ó. Colculote f he power in wolts used if youexert 50 joules of work in 5 seconds.@ 2s0w@ lowo 55W@ 45W

| 7. Keisho tokes on hour to ride her bicyclenorth for Z kilometers before reochingthe store. Then she rides south foró kilometers to her ount's house. Whichof the following describes Keisho'svelocily on her trip to the store?@ ó kilometers per hour@ Z kilometers per hour@ ó kilometers per hour south@ Z kilomelers per hour north

| 8. When you roise or lower o flog on of logpole, you ore using o simple mochinecol led o@ lever.@ wheel ond oxle.O Pul ley'@ incl ined plone.

19. Exploin why the onswer you selectedfor Queslion I B is best. For eoch of theonswers you do not select, give o reosonwhy it is not lhe besl choice.

i zo. SMffiF PersuosiveCreote three posters thot illustrote ondexploin eoch of Newton's lows of motion.Use o slogon or phrose to summor¡zeeoch of the lows. Use the word inerfíoin the first slogon, occelerofion in thesecond slogon, ond ocfion ond reocfionin the th i rd s logon.

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úr" rot"r io l . f rom home to moke o modeloirplone. Try di f ferent moter iols ond modelsto see which f l ies higher ond foster.

Even in his own l i fetime, Isooc Newtonwos considered one of history's greotestscientists. He hod o deep curiosity obout ihenoturol world. He looked for cleor ond logicolwoys to exploin everything he noiiced. Hedid experiments with l ight to exploin howroinbows form. He invented o new kind oftelescope to study the sky. He put togetherideos from oll different oreos of science in

very creotive woys. Among the results were his fomous lowsof motion. These lows, including his definit ion of force, cousedpeople to think obout science in o new woy.

Isooc Newton groduoted from Combridge University inEnglond in I óó5. For more ihon 30 yeors, he wos o teocherthere. Loter in l i fe, he become the heod of Englond's mint,which coined the notion's money. Portly becouse of hisscientif ic bockground, he wos oble to cotch mony peoplemoking foke money ond bring them to justice.

Newton's work goined him the respect of scientiststhroughout Europe. Centuries hove possed since Newton'sdeoth. Yet, even todoy, his theories form the bosis of our

| . t . l . lunoersronorno or Ine un rverse.