physical science.pdf

8/14/2019 Physical Science.pdf

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what makes up matter.that all matter has mass, weight,volume, and density.how the properties of substanceschange.ways that substances combine toform new substances.

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density mixture

physical change


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chemical change

solubility

solution

solute

solvent

Chapter 11 Vocabulary

density page 326mixture page 328solution page 330solute page 330solvent page 330solubility page 331physical change page 332

chemical change page 336


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Explore What properties cause liquidsto form layers?Materials What to Do

Pour in each liquid inthe order they are listedin the materials section.

Observe that the liquidsform layers.

Gently drop in a smallpaper clip. Watch untilit stops sinking. Next,

drop in a piece ofStyrofoam. Wait untilit stops. Then drop in apiece of rubber band.

Explain Your Results1. Infer Based on your observations,

which liquid has the highest density? thelowest density? How do you know?

2. Which object has the highest density?the lowest density? How do you know?

Because of theirdifferent properties,these liquids canform layers.

corn oil

water (with redfood coloring)

dishwashing liquid

corn syrup

cup

small paper cliptiny piece of Styrofoam

piece of rubber band

You makeinferences whenyou developideas based on

observations.

A liquid with a higherdensity will sink under aliquid with a lower density.


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Day Action Observations1 We put water in the freezer. Water was liquid.2 The water was frozen into

ice. We put the ice into aglass of water.

The ice floated on the water.

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Compare and ContrastComparing and contrasting information helps youunderstand some kinds of writing. We compare when wesay how things are alike and contrast when we say how

they are different. Writers use clue words to signal likenesses and differences.

The most common clue word for likenesses islike . Clue words such as yet, but, and however signal differences.

In the lab report below, the student made observations thatcompare and contrast the water and ice in the activity.

Lab Report

Ice is the same substance as water. But the temperature of ice is lower. Thatswhy its a solid instead of a liquid. So we were surprised that the ice floated onthe water. Later, the ice was beginning to melt. It was smaller than before butstill floated on the water.

Apply It!Use a graphic organizerlike the one shown. Writeobservations thatcompare and contrast

ice and water.

Alike Different


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You hear the liquid water rushingbeneath the boat. You glancedown at the deck. You notice the

puddles from yesterdays rainhave disappeared. The water hasevaporated into the air aroundyou. As the boat approaches theiceberg, you reach out to feel asolid wall of water. How doesthe water that surrounds youchange form?

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Lesson 1

What is matter? All forms of matter are made up of tiny particles that are

too small to see. The way these particles are arranged andmove determines whether the matter is a solid, liquid, or gas.

Properties of MatterLike ice, water, and air, you are made of matter. All

living and nonliving things are made of matter. Matteris anything that has mass and takes up space. Scientistsuse different ways to identify matter. One way is by itsproperties. You can identify many properties of matter byusing your senses. For example, you can look at the color,size, and shape of some matter. You can touch matter todecide if its texture is rough or smooth, soft or hard. Youcan recognize some matter by its smell and taste.

Testing MatterSimple tests can show other properties of matter.

You can see how matter reacts if you heat or cool it, forexample. You can see if matter is affected by a magnetor if it allows electricity to pass through it. You can hitmatter with a hammer to see if it shatters or is not evendented. You can see how flexible it is. Does it breakor does it simply bend however you move it? You canobserve what happens when you place matter into water.

Does it float or does it sink to the bottom? You can try tomix it with other matter. Does some matter disappear?Or does something new seem to take its place?

1. Group five different objects in yourclassroom by properties. Describe the properties.

2. Collect pictures or small objects thatshow different textures of matter. Make a collage withthe pictures or objects you collect.


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States of Matter

Using different instruments, scientists have learned thatall matter is made up of tiny particles. These particles arearranged in different ways. These particles also move. Thearrangement and movement of the particles in matterdetermine its form, or state. The three most familiar statesof matter are solid, liquid, and gas.

Usually substances on Earth exist naturally in justone state. Can you name a substance that you can findnaturally in all three states? If you said water, you are right.You can find water naturally in all three forms. Liquid wateris the same substance as the solid called ice and the gas

called water vapor.

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SolidsAt temperatures of 0C or below, the shape of an

ice cube is the same whether it is on a plate or in acontainer. A solid is matter that has a definite shape

and usually takes up a definite amount of space. Itsparticles are closely packed together. The particles havesome energy. They move back and forth, but they do notchange places with each other.

LiquidsWater takes the shape of any container into which

you pour it. If you pour the water in the container ontoa table, its shape changes, but the amount of water staysthe same. Matter that does not have a definite shape,but takes up a definite amount of space, is a liquid. In aliquid, the particles are not held together as tightly as ina solid. The particles of a liquid are able to slide past oneanother.

GasesIn the gas state, water is called water vapor. It is

invisible. Water vapor and several other gases make upthe air that is all around us. Like a liquid, a gas takesthe shape of its container. Unlike a liquid, a gas expandsto fill whatever space is available. A gas always fills thecontainer it is in. The particles in a gas are very far apartfrom one another and move in all directions. Particles ina gas move around more easily and quickly than thosein a solid.

1. Name the solid and gas forms of water. 2. Draw a diagram to show the arrangement and

movement of particles for one state of matter.

3. Compare and Contrast the movement ofparticles in solids, liquids, and gases.

You cant see theparticles in a solid.This drawing showshow the tightly packedparticles are arranged.

You cant see theparticles in a liquideither. The particles areclose to each other, butthey are not held tightly

together.

The particles in a gasare far apart. Even if you could see them, you would not see theparticles arranged inany special way.


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Lesson 2

How is matter measured?You can use metric rulers, balances, and graduated

cylinders to measure some properties of matter.

MassDid you know that your weight on

Earth is about six times as much asyour weight on the Moon? Thatsbecause your weight depends upon

the force of gravity. Your weight onanother planet might be much greaterthan your weight on Earth, but yourmass is the same. While your weight onthe Moon might be less than your weighton Earth, your mass is the same whereveryou go.

Scientists use mass because they want ameasurement that will not change if the objectis moved to a different location. Mass is themeasure of the amount of matter in an object.The mass of an object does not change unlessmatter is added to or removed from it.

Using a Pan BalanceYou can use a pan balance to

compare a mass that you knowwith one that you do not know.When the pans are level, the twomasses are equal.

Suppose you found the mass of thetoy in the picture and then took it apart.Next you measured the mass of each partseparately and added them together. Whatdo think the total would be? The total mass

of all the parts is the same as the mass of theassembled toy. The toys mass is 23 grams.

The pan balance showsthat the mass of the toy,23 grams, is equal to thetotal mass of its parts.

23 grams


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Suppose someone who did not see the toy takes all ofthe parts and makes a toy that looks very different fromthe one you see. What do you think is the mass of thisnew toy? Thats right, 23 grams. The only way to changethe toys mass is to add parts or not use all of them. Thisis because the only way to change the total mass of anobject is to either add matter or take it away.

Metric Units of MassScientists use metric units when they measure and

compare matter. The gram is the base unit of mass inthe metric system. Some of the metric units that areused to measure mass are milligram (mg), gram (g),and kilogram (kg).

Like our place-value system, the metric system isbased on tens. Prefixes change the base unit to larger orsmaller units. For example, 1,000 milligrams are equalto 1 gram, and 1,000 grams are equal to 1 kilogram.

The mass of alarge paper clipis about 1 g.

The mass of a

nickel is about 5 g.

The mass of themilk in this cartonis about 1,000 g,or 1 kg.

1. Explain why your mass isthe same wherever you go.

2. The mass of a nickel isabout 5 g. About how many nickels areneeded for a mass of 1 kg? Rememberthat 1 kg 1,000 g.

23 grams


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VolumeTake a deep breath. As your lungs fill with air, you

can feel your chest expand. This change in your lungsize is an increase in volume. Volume is the amount ofspace that matter takes up.

Like mass, volume is a property of matter that canbe measured. One way to measure the volume of asolid such as a box, is to count the number of unitcubes that fill it. Another way to find the volume is touse a ruler to measure the length, width, and heightof the box. Then multiply the measurements. If a boxmeasures 5 cm long, 2 cm wide, and 8 cm high, then

the volume of the box is 5 cm 2 cm 8 cm, or80 cubic centimeters.

Scientists often use metric units when they measure.The table below shows how the units of length in themetric system are related. Some metric units that areoften used to measure and compare the volume of asolid are cubic centimeters (cm 3) and cubic meters (m 3).

Comparing Metric Units of LengthMetric Unit

1 millimeter

1 centimeter

1 meter

1 decameter1 hectometer

1 kilometer

Equivalent

0.001 meter

10 millimeters

100 centimeters or1,000 millimeters

10 meters100 meters

1,000 meters

1 decimeter 10 centimeters

The rulers show theboxs measurements,

which can bemultiplied together tofind its volume.


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Volume of LiquidsLiquids do not have a definite shape.

To measure a liquid, you use a measuringcontainer, such as a graduated cylinder.

A graduated cylinder is marked with metricunits. Some metric units used to measurevolume are milliliter (mL) and liter (L).One liter is equal to 1,000 milliliters. Theunits marked on this graduated cylinder aremilliliters (mL).

Volume of Other Objects

A graduated cylinder can be used to find thevolume of solids that sink in water. To measurethe volume of a ball, for example, put somewater into a graduated cylinder. Record itsheight. Then place the ball into the cylinder,and record the height of the water again.The ball has pushed away some of the water.The water level has risen the same number ofmilliliters as the volume of the ball. A volumeof 1 mL is the same as 1 cm 3.

1. What metric units are used to

measure the volume of solids? of liquids? 2. Express 2 L in milliliters.

The water level in this graduatedcylinder rose from 50 mL to55 mL when the ball was added.The volume of the ball is55 mL 50 mL 5 mL or 5 cm3.

Examples of Metric Lengths What Was Measured

Thickness of a CDLength of a paper clip

Measurement

1 mm32 mm

Thickness of a CD case 1 cm or 10 mm

1 m12 m

11 km or11,000 m

10,000 km

Height of a doorknob from the floorLength of a school bus

Length of 440 blue whales placedend to end

Distance from the North Pole tothe equator


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Density Sometimes you need to know how much

mass is in a certain volume of matter. Supposea friend asked you, Which has more mass,a piece of wood or a piece of steel? Your firstresponse might be, How big is each piece?In order to compare the masses of two objects,you need to use an equal volume of each. Theamount of mass in a certain volume of matteris a property called density. For example, ifthe pieces of wood and steel are the same size,the piece of steel has more mass and a greater

density than the wood.

Finding Density You find the density of a substance by

dividing its mass by its volume. The units oftenused for the density of solids are grams percubic centimeter. You write density as a fraction:

mass in gramsvolume in cubic centimeters . The density of water is 1

because 1 gram of water has a volume of1 cubic centimeter.

An objects density determines whether itfloats or sinks in a liquid. You can see in thepicture at the right that liquids can float on topof other liquids. For example, water floats ontop of corn syrup because its density is less thanthe density of the corn syrup.

A peeled orangesinks, but an unpeeledorange floats.

cooking oil

corn syrup

water


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Comparing DensitiesThe substances with the greatest densities are

near the bottom of the cylinder. The substanceswith the least densities are near the top.

You can also compare the densities of theobjects that are floating. The density of the grapeis less than the density of the corn syrup butgreater than the density of water. The densityof the plastic block is greater than that of thecooking oil but less than the density of water.The cork has the least density of the liquids andthe other objects in the picture.

An ice cube floats in water because the densityof ice is less than the density of water. But itsjust a little less! So most of a floating ice cube isbelow the surface.

1. Explain why steel sinks in water and cork floats. 2. An unpeeled orange floats in water, but a

peeled orange sinks. What can you concludeabout the density of an unpeeled orange?

3. Scientists usesubmersibles (submarines) to explore oceans.Use library books or the Internet to find outmore about how submarines sink or float.

Life Jacket Life jackets or life preservers aremuch smaller than you are. Butthey help you stay afloat in water.They are filled with foam or othermaterials that have densities lessthan water. A life jacket pushessome of the water out of the way

just like the ball in the graduatedcylinder. The life jacket helps youkeep your head above the surfaceof the water.

The liquids and otherobjects have differentdensities.


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Lesson 3

How do substancesmix?

Mixtures are made by physically combiningtwo or more substances. The solids, liquids,or gases in a mixture are not chemicallycombined. They can be easily separated.

Mixtures

You may have eaten a snack madefrom a mixture of nuts, dried apricots,and raisins. Each ingredient in thismixture keeps its own taste and shape.

A mixture is a combination of twoor more substances. Substances in amixture can be separated. This meansthat they are not chemically combined.

Peas, carrots, and corn can be combinedin a mixture. In fact, you can buy abag of frozen mixed vegetables at thestore. Each vegetable can be sortedinto separate piles. The peas, carrots,and corn taste the same whetherthey are separated or mixed together.All substances in a mixture that areseparated out have the same propertiesas before they were mixed.

A magnet can be used to separatethe safety pins from the mixture.

The yellow beadsfloat in water.


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Some substances can mix physically withother substances. The makeup of a mixture canvary. A mixture does not necessarily contain aspecific amount of each substance. They are notjoined together chemically, so each substancein the mixture keeps its own properties. You caneasily see the properties of each substance thatmakes up the beads, marbles, sand, safety pins,and salt mixture shown here.

You can easily separate the ingredients inmany mixtures. Since safety pins are attractedto a magnet, you can use a magnet to separatethem from the rest of the mixture. Then, you

can put the rest of the mixture in water. Youcan use a spoon to skim off the floating beads.If you pour the water through a filter, you canremove the sand and the marbles. Then, afterthe water evaporates, the salt will be left.

You separated the substances of this mixture,but you did not change the properties of any ofthe individual substances.

1. When the bead, marble, sand,and salt mixture is put into water, the yellowbeads float. What does this tell you about thedensity of these yellow beads?

2. Expository In yourscience journal, write a numbered set ofinstructions for separating a mixture of paperclips, wood chips, gravel, and sugar.

After the water fromthe mixture ofsalt and waterevaporated, salt

was left behind.

Filter paper can beused to separatesolids from liquids.


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Solutions

If you stir salt and water together, you make amixture. You cannot see the salt in this mixturebecause it has broken into very small particles. Ithas dissolved in the water. The salt and water is aspecial kind of mixture called a solution.

In a solution, one or more substances aredissolved in another substance. The most commonkind of solution is a solid dissolved in a liquid,such as salt in water. In this kind of solution, thesubstance that is dissolved is the solute. In asolution of salt and water, the salt is the solute. A

solvent is the substance that takes in, or dissolves,the other substance. Usually there is more solventthan solute. In salt water, the solvent is water.

Common Solutions

In the oceans, salt and other mineralsare dissolved in water. Ocean water is asolution. But a solution does not have

to be a liquid. The air you breathe,for example, is a solution madeup of gases. The steel usedfor buildings and cars isa solution. During theprocess of making steel,carbon and iron, two solids,are melted into liquid form.Then the carbon is dissolvedin the iron.

Club soda is a solution madeup of a gas dissolved in aliquid. The solubility of the gasdecreases as the temperatureof the solvent increases. Thatis why a club soda goes flat

faster when it gets warm. Asthe water becomes warmer,more gas leaves the solution.

The salt isdissolved in

this solution.

salt

Salt dissolvesin water.


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Solubility No matter what you do, you cannot make

sand dissolve in water. The ability of onesubstance to dissolve in another is called itssolubility. Solubility is a measure of theamount of a substance that will dissolve inanother substance. Since sand does not dissolvein water, the solubility of sand in water is zero.

Sometimes you can speed up the process ofdissolving the solute by raising the temperatureof the solvent. This is true for most solutes thatare solids. For example, you can dissolve moresugar in warm water than you can in cold water.

Another way to make a solute dissolve morequickly is to crush it. If you drop a sugar cubeinto a cup of water it will dissolve, but it may

take a while. If you crush the sugar cube intotiny crystals, the crystals will dissolve veryquickly. The reason for this is that more of thesugar particles are touching the water whenthe sugar is in tiny crystals than when it is in asugar cube.

1. What are the parts of a solution? 2. What factors affect the solubility of a

substance? 3. During the Gold

Rush, many people panned for gold. Panningseparates gold from a mixture of gold andother particles such as sand. Use books orthe Internet to find out about the CaliforniaGold Rush.

Instant cocoa dissolvesmore quickly in a cup ofhot water than in a cupof cold water.

sand

Sand does notdissolve in water.


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Lesson 4

How does matterchange?

Matter undergoes physical and chemical changes. In a physical change, the size, shape, or state of the substancechanges. A change that forms a new substance with new

properties is a chemical change.

Physical ChangesIf you cut and fold a piece of paper to make an origami

sculpture, you change only the size and shape of the paper.You have not changed the particles that make up the paper.

A change in the size, shape, or state of matter is anexample of a physical change. A physical changedoes not change the particles that make up matter. Thearrangement of the particles, however, may be movedaround during a physical change.

Are you causing a physical change when you mix saltand water? A solution of salt and water can be compared toa mixture of nuts and raisins. You can separate the nuts andraisins by hand. If you make a mixture of salt and water,the particles are too small for you to separate by hand.However, if you allow the water to evaporate, the salt will beleft behind. Because the particles in a mixture do not changeand can be separated, making a mixture is an example of aphysical change.

Breaking a pencil is a physical change. The pieces of thepencil are still made of wood and graphite. If you sharpenthe broken ends, you can keep using the pencil. Anotherphysical change is tearing. If you tear a sheet of paper intotiny pieces, it still is made of the same kind of matter.

Have you ever made a bowl out of clay? You start with abig blob of clay and form it into the shape of a bowl. Theclay bowl is made of same kind of matter as the original

blob of clay. The clay is just a different shape. It haschanged physically.

A knitter uses aball of yarn.

The yarn isknitted into along strip.

The knitted stripcan unravel intothe same amountof yarn as theoriginal ball.


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1. Sawing wood,

shredding paper, and crushing asugar cube are physical changes.Give examples of three otheractions that are physical changes.

2. A chunk of cheesehas a mass of 450 g. Suppose yougrate this entire chunk. What doyou expect the mass of the gratedcheese will be?

If you unfold the sculpture, you will have the same pieceof paper you started with.

The sculpture is finished.

An origamisculpture begins

with a plainpiece of paper.

The paper is foldedmany times.


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Phase ChangesSuppose you freeze water into an ice cube and

then let it melt. The liquid that results is still water.Ice and liquid water are the same substance indifferent states. These states are called phases.

What causes the particles of a substance to bein one phase rather than another? The answer hasto do with energy. Energy can cause the particlesin a substance to move faster and farther apart.Substances change phase when enough heatenergy is added or taken away. For example, youput liquid water into a freezer to remove heat andmake ice. You add energy to water when you heatit. If you boil water in a pot, some of the waterbecomes water vapor. Phase changes areexamples of physical changes that can bereversed by adding or removing energy.Every substance changes phases at adifferent temperature. 250C

Some woodburns.

230CPaper startsburning.

100C Water boils. Water vaporcondenses.

0C Water freezesinto ice. Ice meltsinto water.

Effects of Temperatureon Matter


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The melting point is a physical propertythat helps identify a substance. Thetemperature at which a substance melts isthe same temperature at which it freezes.

This is also true when a substanceevaporates, or changes from a liquid to agas. The boiling point is the temperatureat which a substance changes froma liquid to a gas. The temperature atwhich the substance evaporates is thesame temperature at which it condenses.Condensation is the changing of a gas intoa liquid.

1. How does adding or takingaway heat energy cause changesin matter?

2. Descriptive Supposeyou are a drop of water. Describe in yourscience journal what happens to youwhen heat energy is added or taken away.

328CLead melts.

1535CIron melts.

Energy and WaterThese phase changes areexamples of physical changes.

Whether water is a solid,liquid, or gas, it is still water.

In a solid, the particles are

attracted to each other. Theyare close together and donot move very much.

Adding heat increases theenergy of the particles.The particles move faster.Solid ice changes phase bymelting into a liquid.

Boiling water adds even moreheat energy. The particles moveeven faster and farther apart.Liquid water changes phase togas water vapor.


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Burning wood reacts veryquickly with oxygen in the air.The new substances formed by

this change are ashes, carbondioxide gas, and water vapor.

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Chemical ChangesIf you leave an iron nail in a damp place,

it will rust. Suppose you compare the rustwith the iron nail. You will find that thenail and the rust have different properties.The color and hardness of rust and iron aredifferent. Rust is a different substance thatresults from a chemical change in the ironnail. Unlike a physical change, a chemicalchange produces a completely different kindof matter. In a chemical change, particles ofone substance are changed in some way to

form particles of a new substance with differentproperties.

You can see evidence of a chemical change,such as the bubbles in the picture. Or the newsubstance may be a different color. It mayhave a different smell or temperature. Manychemical changes give off heat. In each case,the chemical properties of the materials that

were mixed have changed.

Rust forms slowlyas oxygen fromthe air combines

with the iron inthe gear.

The acid in vinegar reacts with baking soda and formsbubbles of carbon dioxide. Thebubbling and fizzing show thata chemical change is occurring.

Tarnish, like rust,results from a chemicalchange when certainmetals, such as silver,react with air.


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ElementsIn a pure substance, particles are alike. The

simplest pure substances are called elements. Thereare more than 100 known elements. Scientists have

organized information about these elements ina chart called the Periodic Table. Each element isin a particular row and column in the table. Theposition in the Periodic Table gives informationabout the makeup and properties of each element.Each element has its own symbol. The letter orletters in the symbol are sometimes from theelements name in Latin.

1. What is a chemical change? 2. When you chew food, are you causing physical or

chemical changes to the food? 3. Compare and Contrast How are rusting and

burning different? How are they alike?

The Periodic Table


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Investigate How can you changethe properties of glue?Mixing glue with another substance can change its properties. The propertiesof the new substance are different from the properties of the original substances.

Materials What to DoMeasure 30 mL of glue into asmall measuring cup. Pour it intoa larger cup. For fun, addfood coloring.

Add 15 mL of water to the cup. Stir the mixture.Observe its properties.

Observe what happens.

Add 15 mL of borax solution.Stir.

glue and food coloring

smallmeasuring cup

borax solution

cup and spoon

safetygoggles

Wear safety goggles.

After you makeobservations, you can collect

your data in achart.

water


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Wash your hands when fin ished.

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Explain Your Results1. How are the physical properties of the

new substance and the glue alike? Whatdifferences did you observe ?

2. Would the new substance be a good glue?Explain.

Play with the new mixture.Investigate its properties.

Record the data you collect about the propertiesof the glue and of the new substance.

C o u l d y o u d o t h i s w i t h g l u e ?

If you used a different amountof borax solution, would thesubstance have the sameproperties? Develop a plan fora safe, simple investigation toanswer this question or oneof your own. With teacherpermission, carry out the plan

you designed.

Property Observations

Glue New Substance

Color

Texture

State of Matter(solid, liquid, gas)

Odor


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The table lists some common liquids and theirdensities. Each density is rounded to the nearest tenth.

Density is written as a decimal number. You can usea number line to compare and order decimals. Ona number line, the values increase as you move tothe right and decrease as you move to the left. Forexample, on the number line below, 0.7 is less than0.9, so 0.7 is to the left of 0.9.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

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Substance Density ( gramscubic centimeters ) A Corn Syrup 1.4B Cooking Oil 0.9C Ethyl Alcohol 0.8D Gasoline 0.7E Water 1.0

D C B E


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Use the table and number line on page 340 to answerthe following questions.

1 Which point on the number line represents thedensity of cooking oil?A. Point E B. Point BC. Point C D. Point D

2 Where on the number line would you plot the pointfor the density of corn syrup?F. to the left of Point DG. to the left of Point EH. at Point EI. to the right of Point E

3 How many liquids in the table have a greaterdensity than gasoline has?A. 1 B. 2C. 3 D. 4

4 Suppose you poured liquids AE into a graduatedcylinder. Which is the correct order of liquid layers

frombottom to top ?F. D, B, C, E, AG. D, C, B, A, EH. A, D, C, B, EI. A, E, B, C, D

An object with a density that is less than1.0

gramcubic centimeter

floats in water. List ten itemsfrom your home. Predict whether each itemwill float or sink. Record your predictions.Then test each item. Indicate which items

have a density that is less than 1.0gram

cubic centimeter .

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Use Vocabulary

Use the vocabulary term from the list abovethat completes each sentence. 1. _____ is the ability of one substance

to dissolve in another substance.

2. The property that compares the massof an object with its volume is _____.

3. In a solution, the _____ is thesubstance that takes in, or dissolves,the other substance.

4. A change in size, shape, or state ofmatter is a _____.

5. The substance in a solution that isdissolved is called the _____.

6. The quarters, dimes, nickels, andpennies in a coin purse are a _____.

7. New substances with differentproperties are formed by a _____.

8. In a _____, substances are dissolved

in other substances.

Explain Concepts 9. What does it mean to say that a

liquid has a definite volume but nodefinite shape?

10. Suppose you have 50 mL of water ina graduated cylinder. After you placea marble in the cylinder, the waterlevel rises to 78 mL. What is thevolume of the marble? Explain howyou know.

11. Infer A balloon filled with heliumgas rises in the air. What might youinfer about the density of heliumcompared with the density of air?

12. Classify Tell whether each of thefollowing involves a physical changeor a chemical change. frying an egg

breaking a balloon boiling water toasting bread

chemicalchange (p. 336)

density (p. 326)

mixture (p. 328)

physical change (p. 332)

solubility (p. 331)

solute (p. 330)

solution (p. 330)

solvent (p. 330)


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13. Observe Suppose you put asubstance in a glass of water and stirthe mixture. Then you observe that allof the substance settles to the bottomof the glass. From your observation,what might you conclude about thesolubility of the substance?

Compare andContrast

14. Explain how physical and chemicalchanges are different. How are theyalike? Use a graphic organizer likethe one shown.

Test PrepChoose the letter that best completes the

statement or answers the question. 15. Matter is anything that has mass and

is living. takes up space. is not broken. holds water or air.

16. When most liquids are cooled to thefreezing point, the tiny particles ofmatter that make up the liquid

move quickly in all directions. move out into the air. come closer together. move farther apart.

17. A chemical change results in a

loss of matter or energy. solution. phase change. different kind of matter.

18. You make a solution when you mix salt and water. sugar and cinnamon. vegetables in a salad.

cheese sauce and macaroni. 19. Explain why the answer you chose

for Question 16 is best. For eachof the answers you did not choose,give a reason why it is not thebest choice.

20. Expository

Since ice is less dense than liquidwater, it floats. Explain what youthink would happen to the plantsand animals living in a Minnesotapond if ice were more dense thanliquid water.

Alike Different


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What if your pencil bent every time you tried towrite with it? What if your pillow were made ofmetal? All of the properties of matter are important indeciding how it is used. Matter can be hard or soft,rough or smooth. It can be sticky, stretchy, spongy,or slick. Some chemists who work for NASA makematter that can be used on space vehicles.

Metals used for space shuttles must not be damagedby a lot of heat. Some metals are better than othersat handling heat. Chemists can also mix metals tomake a material that can stand more heat than eithermetal could on its own. The Kennedy Space Centeris close to the ocean. There is so much salty waternearby that metals often rust. The metals NASA usescannot rust easily.

Plastics are also important materials used in space.They may need to be hard and slick, or soft andrubbery. Chemists can make plastics that have manydifferent properties.

Analytical chemists need to understand math andscience well. They must graduate from a college oruniversity. They can work in many different places.

Dionne Broxton Jacksonis an analytical chemistat NASA. She works

with metals.

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Gather different materials in your home,such as kitchen utensils, toothbrushes,and food containers. Make a list in yourscience journal of which products you

think might be useful in space. E C N T L 1 0 9 8 7 6 5 4 3 2


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the difference between heat and temperature.three ways heat is transferred.

345


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346

thermal energy

conductor

insulator


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xes TK

thermal energy page 351

conduction page 354conductor page 355

insulator page 355convectioncurrent page 356radiation page 358

Chapter 12 Vocabulary conduction

convection current radiation

347


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348

Explore How can you make things warmer?Materials What to Do

Touch a paper clip. Observe .Does it feel warm?

Bend one end back and forth

4 times quickly. Quickly touchthe bent part. Observe.

Touch an eraser. Rub it on paperfor 1 minute. Quickly touch the surface yourubbed on the paper. Observe.

The paper clipcould break.

Rub your hands together for 15 seconds.Observe.

Explain Your Results1. How did bending change the paper clip?2. What did you observe when you rubbed

the eraser against paper? What happenedwhen you rubbed one hand against the other?

3. What can you infer about what happenswhen one object rubs against another?

You can use whatyou learn byobservation to help youmake accurate

inferences .

safety goggles

eraser

sheet of paper

clock with a second hand(or timer or stopwatch)

paper clip


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Cause Effect

349

Cause and EffectA cause may have more than one effect. An effect may have more thanone cause. An effect may cause something else to happen. Clues such asbecause, so, since, thus, and as a result that signal cause and effect canalso help you make inferences.

Think about what you know and have observed about hot-air balloons andheat transfer as you read the interview with a balloonist. Cause and effectare highlighted.

Magazine Interview

Extreme Sports for Kids: I understand that

you enjoy riding in hot-air balloons. Justwhat causes a hot-air balloon to rise?

Balloonist: It all results from heat transfer. A balloon is like a hugeplastic bag. To inflate the bag, I fill it with air. Then I heat that airwith a burner. A flame reaches into the plastic bag.

ESK: Then does heat transfer take place?

Balloonist: Yes, the air inside the bag gets warm and less dense thanthe air around it. The cool air sinks under the warmer air. As a result,

the balloon goes up!ESK: I know that air expands when it gets heated because particlesare moving really fast and really far apart!

Balloonist: Youre right. Lets take a ride!

Apply It!Make a graphic organizerto help you infer why ahot-air balloon rises.


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350

The red-hot steel flows into an iron mold. Even though

you are wearing a suit that protects you from theheat, you can sense the scorching air! You work inone of the worlds most important industries. You area steelworker. At your mill, iron ores from rocks andminerals are crushed and then heated in giant furnaces.They become liquid steel. Your job is to cast that moltensteel into 2-ton blocks called ingots. The steel that youpour hardens into an ingot. The ingot is placed in ahuge heated pit where the temperature reaches 1200C(2,200F). How does heat move?


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351

Lesson 1

Why does matterhave energy?Energy is the ability to cause change or do work.Heat is the total energy of moving particles in matter.The more particles something has, the more internalenergy it contains.

Energy in Matter

Rub your hands together. Whathappens? You just used energy tomake heat! Energy is the abilityto change something or do work.Cool hands changed to warm ones.Whenever the location, makeup, orlook of something changes, energyis used. All changes need energy!

All matter is made up of tinyparticles that are always moving.In a solid, particles are closelypacked. They move slightly aroundfixed positions. In a liquid, they are close together.They flow freely past one another. In a gas, particlesare very far apart. They move in all directions.Particles in an object move because they have energy.

As an object becomes hotter, its particles move

faster. As the object cools, the particles move moreslowly. Thermal energy is energy due to movingparticles that make up matter. We feel the flow ofthermal energy as heat.

1. What is energy? 2. Descriptive You are in a sunny

place wearing a T-shirt and shorts. Write a paragraphin your science journal that describes changes toyou and to a piece of chocolate on a table near you.

The colors in thisthermogram, or

heat picture,show the differentamounts of heatenergy.


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Measuring Moving ParticlesHave you ever seen a thermometer like the one at the

bottom of the page? You measure temperature with it.Most thermometers are thin glass tubes that are joined toa bulb that holds colored alcohol. The number linesmarked on the outside of the tube show degrees. Onenumber line is scaled in degrees Celsius. The other isscaled in degrees Fahrenheit. A thermometer is based onthe idea that matter expands when its particles movefaster and contracts when they slow down.

If a thermometer touches matter withparticles that are speeding up, particles in

the liquid inside the thermometer speedup too. They move farther apart. Becausethe liquid expands more than the glasstube, it moves up the tube. The reading onthe number line shows a greater number ofdegrees. If the particles slow down, the liquidcontracts. The shorter column in the tubeshows fewer degrees.

The thermometer must be on or inwhatever its measuring. If its nottouching the material, it might notmeasure particle motion correctly.

How a Thermometer

WorksThis thin glass tube has a bulbfilled with colored alcohol.The bulb is placed on or inthe material being measured.Depending on the materialstemperature, liquid travels up ordown the tube. The thermometerin the photo is measuring thetemperature of the air. The number

lines on the outside of the tubeshow degrees Celsius on the rightand degrees Fahrenheit on the left.

352

The water in both pots isat the same temperature.The larger pot has moreparticles and thereforemore thermal energy.


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Heat and TemperatureIf you wonder how hot or cold something is, you

might think about its temperature. When a materialhas a high temperature, its particles move fast. But

temperature is not a measure of how much heat thematerial has.

Many of us mix up the meanings of heat andtemperature. The difference is in the movement ofparticles of matter. Temperature is the measure of theaverage amount of motion of particles in matter. Itmeasures the average energy. Thermal energy is thetotal energy of those moving particles. It measuresboth how fast the particles move and how many aremoving. Heat is the transfer of thermal energy from

one piece of matter to another. For example, think of a large pot and asmall pot that are each half filled with boilingwater. Because the large pot holds morewater, it has many more water particlesthan the small pot has. More particles meanmore energy of motion. The large pot has

more thermal energy. Since the water ineach pot is boiling, the temperature of

the water in both pots is the same.The average amount of motion ofparticles in the water is also thesame. So, the size of the pot doesnot affect temperature !

1. What happens to the motion of particles when an objectbecomes hotter?

2. Explain why a large pot of water takes longer to begin boilingthan a small pot. Both pots started with the same temperatureof water, and burners for both pots are set on high.

3. Cause and Effect What causes liquid in a thermometerto travel up and down the tube?

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Fewer particlesin the smaller potmean less thermalenergy.


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Lesson 2

How does heat move?Heat is the transfer of thermal energy. Heat can be moved in

several ways. The transfer of heat energy affects climate.

Conduction

Thermal energy flows from somethingwarm to something cool. The transfer ofthermal energy betweenmatter with different

temperatures is heat. A heatsource is anything that givesoff energy that particles of mattercan take in. Remember when yourubbed your hands together earlier? Youused mechanical energy to make heat. Whensolids are touching, heat energy moves byconduction. Conduction is the transfer of heatenergy by one thing touching another.

Suppose that you stick a strip of wax on thehandle of a metal spoon. Then you place thelower part of the spoon in boiling water. Whathappens to the cool spoon? Thats right, it getshot! The spoons particles that touch the waterstart to move. As they move more quickly,they crash into the particles in the spoonshandle. More and more crashes take

place. Soon, heat energy from thewater moves throughout the spoon.The transfer continues until both thewater and the spoon are the sametemperature. How do we know that theheat energy has moved? The hot spoonhandle and the melting strip of waxare proof! A wooden spoon does notconduct heat energy. Its handle stayscool, and the strip of wax on itdoesnt melt.

Heat energy from theboiling water moves

through the metalspoon. The heatcauses the piece of

wax to begin melting.


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1. What is thedifference between an insulatorand a conductor?

2.Use reference sources such asencyclopedias, nonfiction books,and the Internet to find othermaterials that are used asinsulators. Explain where the

material is used and how itworks as an insulator.

Conductors and Insulators

The raised hairs of Japanese macaquemonkeys trap heat. Themonkeys share bodyheat to keep warmin the snow.

355

Metal Some materials let heat move through them more easilythan others do. A material that readily allows heat to move is aconductor like the metal spoon. Many metals, such as aluminum,

copper, and iron, conduct heat well. If you place an iron pan ona burner or other heat source, it gets hot quickly.

Wood You also know that some thingslike the wooden spoondonot get too warm even when they touch something hot. They areinsulators. Aninsulator is a material that limits the amount ofheat that passes through it. Have you noticed that many pots andpans have wooden handles? Thats because wood is a great insulator.

The wooden paddle in the photo does not conduct heat to the hands of theperson taking the pizza from a hot oven. Heat moves around the paddle.

Marble Since ancient times, marble has been used in buildingsand monuments because it is strong and beautiful. It resists fires anderosion. Marble is also an insulator. A slab of marble is helpful in thekitchen. Its cool, smooth surface is a perfect place to mix tasty treats.

Plastic Do you know why so many foods are served in foamcontainers? The plastic foam that is used to make the containers hasmany small air pockets. The plastic is not the only insulator. Air is agood insulator, too. The plastic and air insulators keep the food at theright temperature.


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Convection

If you dont like the heat, get out of the kitchen! Have youfelt how warm a kitchen gets when a stove is on? Its the resultof convection working! In convection, a fluid moves from placeto place. A fluid is a substance that flows but has no definiteshape. Gases and liquids are fluids.

A pattern of flowing heat energy is a convection current.A convection current forms when heated fluid, such as air,expands. It becomes less dense than an equal volume of thecooler air around it. The cooler air sinks below the warmer air.The warm air is forced upward, and the pattern continues. Thecool air warms and is forced upward by colder air.

Look at the two mobiles in the photo below. Can you find theheat source? Its the candles. As the energy from the burningcandles heats the air above them, the air particles move faster.The particles move farther apart as they take in the energy. Thismakes the air less dense. Cooler air rushes under the less denseair. It pushes the warmer air upward. As long as the candlesthe heat sources are burning, movement of the rising warmair will make the spiral twirl and the blades spin.

One kind of much larger convection current shapes ourweather. Uneven heating of the air around Earth causescurrents that cover thousands of kilometers. They make Earthsmajor wind patterns.

1. How does a convectioncurrent form?

2. Choose a major cityin your state. Use the Internet or othersources to find the average temperaturefor each month of the year. Display yourdata in a bar graph.

keyword: convection current code: 4 356


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357

Warm fluid ispushed upward.

Cooler fluidmoves downunder warmerfluid.

Warm fluid is

less dense.

Cooler fluid ismore dense.

Radiators in BuildingsA radiator heats the air by convection. Water is heated in a boilerthat is often located in the basement. Then the hot water or steamis pumped into pipes throughout the building. The pipes lead intoradiators in each room. Radiators are made of various metals such ascast iron. As the hot water or steam moves, some of its heat energypasses through the walls of the radiator into the air. Convectioncurrents move the air to heat the entire room. The cooler water returnsto the boiler through another pipe. The heating cycle begins again.


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Radiation

You know that the Sun is a major energy source.Every time you get warm in the Sun, you feel radiation.You feel it when you sit near a fire too. Radiation

is energy that is sent out in little bundles. When theradiant energy hits you, the particles in your skin movemore quickly. You feel warm.

Radiation can travel through matter or empty space.Dark-colored or dull surfaces absorb radiation. Butpolished, shiny surfaces reflect radiant energy or letit pass. Clear materials such as air and glass allowradiant energy inside. They also prevent heat loss

through convection. That is why greenhouses are made of materialssuch as plastic or glass. In a greenhouse, radiation provides anenvironment where plants grow regardless of the climate outdoors.People control the temperature, light, and moisture the plants receive.

Other objects that send out light also send out heat. For example,a pet lizard might need a special light to stay warm. The light sendsout heat. Perhaps youve seen special lamps that restaurants use tokeep food warm.

Radiation is different from conduction and convection. Conductiondepends on the crashes of particles in a substance. Convection needsthe spreading out of a fluid when particles crash. But radiation doesnot need particles. It happens all by itself. Radiation can moveenergy great distances, like from the Sun to Earth.

Heat transfers through radiation in different ways. Have youwarmed cold hands near a fireplace? When you do, energy movesto your hands by radiation. Like all thermal energy, radiationmoves from warmer areas to cooler ones.

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Radiation from theSun passes throughthe windows of agreenhouse.


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Conduction, Convection,and Radiation

Once the Suns energy reaches Earth, Earthssurface heats up. Then conduction takes place.

Earths surface transfers heat to the air. Earthwarms the air around you. And Earth is heatedby the Sun.

But its not just conduction that is happening!Convection currents form as the air is heatedby Earths surface. That warm air expands andrises. As the rising air cools, the water vapor init condenses and falls to Earth as rain or snow.

Convection currents in the air cause Earthswind and rain patterns .

The radiant energyfrom the Sun warmsEarths surface.

Sun

Earth

Radiantenergy

1. How does energy from the Sun reach Earth? 2. Cause and Effect What causes Earths

surface to get warm?3. Expository In your science

journal, write a paragraph that explains why agreenhouse might be part of a flower shop.

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Materials What to Do Measure carefully. Pour 300 mL ofwarm water into cup A. Pour 150 mLof warm waterinto cup B.

Temperature of Water (C)

Cup A(300 mL water)

Cup B(150 mL water)

Before adding ice

After 1 ice cube melts

After 2 ice cubes melt




Investigate How are thermalenergy and temperature different?

300 mL150 mL

Sometimesyou can testa prediction by doing anexperiment.

ice cubes

2 plastic spoons

masking tape

2 large cups and2 thermometers

measuring cup andwarm water

Record the temperature of the water in each cup.

Label the cups.

Number of ice cubescompletely melted

when temperaturereached 10C


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361

Put an ice cube in each cup.Stir each cup gently. Record thewater temperature.

When the temperature in a cupreaches 10C, stop adding icecubes to that cup.

Develop and conduct ascientific investigation to testthe prediction you made.Design any tables, charts,graphs, or diagrams to helprecord, display, and interpret

your data.

Explain Your Results1. Which cup had more thermal energy? How

do you know?2. Suppose you used 600 mL of your warm

water. Predict how many ice cubes wouldbe needed to lower the temperature to10C. How could you test your prediction?

To organize and display your data,construct a chart and a graph like theones shown. They will help you examine,analyze, and evaluate the information.

Interpret your chart and graph andthose of other groups. Share yourresults. Do not change your results just because they are different fromthose of other groups.

Cup A

(300 mL water)

Cup B

(150 mL water)

13

12

11

10

9

8

76

5

4

3

2

1

0

N u m

b e r o

f I c e

C u

b e s

After a cups ice cube melts,record the water temperature inthat cup. Add another ice cubeto that cup.

Make a bar graph to show your data.Thermal Energy

Keep stirring untilthe ice cubes melt!


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Both the Celsius and Fahrenheit temperaturescales measure temperature in degrees (),but the degree divisions are not the same.

Notice that, on both scales, zero is alabel for a point. The temperature 5 isread 5 degrees below zero or negative5 degrees.

Suppose you are asked how many40-degree days New York City has in

January. Your answer depends on the scalebeing used. Using the Celsius scale, theanswer would be zero because New YorkCity is never that warm in Januaryor in anyother month! But, New York City might get aswarm as 40F in January.

362

120

110

100

90

80

70

60

50

40

30

20

10

0

-10

-20

-30

-40

-50

250240230220210200190180170160150140

13012011010090807060504030

20100-10-20-30-40-50

C F

Normal bodytemperature

Hot day Roomtemperature

Cool day

Freezing pointof water

Cold day

Very cold day

Boiling pointof water


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Find three different kinds of thermometersat home. They might include a weatherthermometer, a fever thermometer, and ameat thermometer. Make a list of the threekinds and record the highest temperature onthe Fahrenheit or Celsius scale for each one.

Write a paragraph explaining why they aredifferent for different thermometers.

363

Decide which temperature scale is being used in eachsituation: the Fahrenheit scale or the Celsius scale.

The outdoor thermometer reads 25 degrees, and you arewater skiing.

The temperature is 40 degrees and you are wearing a coatat an outdoor football game.

The weather report uses below freezing and abovezero to describe the same temperature.

You heat water to 100 degrees, but the water doesnot boil.


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EffectCauseA steelworker putsa copper rod intoa fire.

Cause EffectDue to

conduction, thepan gets hot.

364

Use Vocabulary

Use the vocabulary term from the list abovethat completes each sentence. 1. The total energy of all the particles in

a body is its _____.

2. A(n) _____ limits the amount of heatthat passes through it.

3. _____ is one kind of energy thattravels from the Sun through space.

4. A material that allows heat to passthrough it is a(n) _____.

5. In a(n) _____, a heated fluid rises andis replaced by cooler fluid.

6. The transfer of energy by one objecttouching another is _____.

Explain Concepts 7. Explain how particles move

differently in a solid, a liquid,

and a gas.

8. Explain why the motion of particlesaffects a thermometer reading.

9. Infer why young trees and plants

are sometimes kept in greenhousesbefore they are planted outdoors.

10. Make a model that shows howheat moves through objects.

11. Predict On a bright, sunny day,you are sitting next to the ice rinkof an outdoor hockey game. Whichwill keep you warmer: a dark, woolblanket or a clear, plastic sheet?

Cause and Effect 12. Fill in the missing cause and effect to

show how heat is transferred in eachsituation.

conduction (p. 354)

conductor (p. 355)

convection

current (p. 356)

insulator (p. 355)

radiation (p. 358)

thermal energy

(p. 351)


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365

Test PrepChoose the letter that best completes thestatement or answers the question. 13. Which is the best conductor?

metal wood marble plastic

14. Temperature is a measure of the total amount of energy in an

objects moving particles. the average amount of motion of

an objects particles. the amount of energy transferred

from the environment to theparticles of an object.

the size of an objects particles.

15. A large pot of boiling water has morethermal energy than a small pot ofboiling water. The temperature of thewater is

higher in the large pot. higher in the small pot. impossible to measure. the same in both pots.

16. A thermometer measures temperatureby showing particles. climate. degrees. volume.

17. When two solids touch, thermalenergy transfers by

insulation. conduction. convection currents. liquids.

18. The Sun warms your skin by insulation. radiation. conduction.

convection. 19. Explain why the answer you selected

for Question 13 is best. For eachof the answers you did not select,give a reason why it is not thebest choice.

20. Informative

Use the Internet to research solarovens. Find out what foods canbe cooked in them and howcooking times compare with thoseof conventional ovens. Write aninformative paragraph to shareyour findings.


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Did you know that the research NASA uses to launch peopleinto space helps people on Earth? For example, some NASAscientists are part of the Thermal Protection Materials and SystemsBranch. Their task is to develop TPS (Thermal Protection System)materials that protect spacecraft and astronauts from heat. Theirresearch produces materials that are lightweight, yet strong andheat-resistantmaterials like those needed to protect steel workers,fire fighters, and others.

Some of the TPS material looks like a carpet. You can roll it out,cut it to shape, and even walk on it! NASAs scientists are testingit to find how well it performs.

NASA uses TPS materials in heat shieldsthat guard spacecraft when theyenter other atmospheres or comeback to Earths. One materialwas used on the MarsPathfinder space probe .

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Would you rather work as a scientist whostudies TPS materials or as one who studiesSSE? Tell a partner which job youd prefer

and why.

But the research provides information for people on Earth too.NASAs scientists use what they know about heat transfer tohelp others. In East Africa, many people use wood to cook food.But wood is hard to find. In some parts of Africa, people spendover half the money they earn each year on cooking fuel.

One of NASAs energy management programs uses satelliteinformation to study Earth from a global point of view. NASAsSurface Solar Energy (SSE) information lets people use theirlatitude and longitude to learn the amount of solar energyavailable for cooking and many other purposes. Solar CookersInternational, a group that helps others learn to cook with theSun, can zoom in on the places where solar cooking can be

best used.NASAs SSE information helps East Africans use the Sun, a

natural resource and great source of heat energy, to cook.Then the people dont need to hunt for wood or spend whatlittle money they have on fuel.

With the Suns energy, East Africans use solar cookers toprepare meals. The Sun is a safe and clean heat source. Solarcooking does not cost much. It does not cause a lot of smoke

or air pollution in the environment. Solar cooking helps peopleharness some of theSuns power!

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Max Planck changedphysics with his theoryabout radiant energy.

Max Planck was a German physicist who livedfrom 1858 to 1947. A physicist is a scientist whostudies matter and energy. While studying heat andradiant energy, he noticed the ways that hot surfacessent out light and took in radiant energy. Plancksaid that objects were able to send out and take inradiation in only little bunches. Planck called thosebunches quanta. His ideas became known as thequantum theory.

Plancks ideas about energy quanta were differentfrom past ideas. Scientists believed energy flowedwithout stopping. They knew that at times energyacted like a wave, but at other times, it acted likea collection of particles.

Then, another physicist, Albert Einstein, usedPlancks theory to explain his own ideas. Einstein

said that light is quantized. He meant that thingsthat send out light do so in little bundles of energy.He thought that radiation was made up of particles,not waves.

The work of one scientist plays a partin the work of others. Plancks ideasaffected Einsteins! Scientists nowknow that radiation has qualitiesof both particles and waves.

The little bundles of energy that Planckdescribed are the power source for solar

cookers. Use the Internet or other resourcesto find other devices that use solar energy.

E C N

T L 1 0 9 8 7 6 5 4 3 2

368


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what causes objects to becomecharged.how electricity moves.why a compass needle pointsnorth-south.ways that electricity and magnetismare related.how magnetism can be transformedinto electricity.

369


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370

static electricity

series circuit

parallel circuit


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371

Chapter 13 Vocabulary

static electricity page 375

electric current page 378

resistance page 379series circuit page 380

parallel circuit page 381

magnetism page 382magnetic eld page 382

electromagnet page 387

magnetism

magnetic eld

electromagnet

resistance

electric current


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72

Materials What to Do Tie a string to a balloon.Rub the balloon with a woolcloth for about 1 minute.

Explore How can static electricity affect objects?

Based on yourobservations ,you madeinferences abouthow chargedobjects affect

each other.

Explain Your Results1. What happened as you brought together your

balloon and your cloth? your balloon and theballoon of another group?

2. Infer How do objects with opposite chargesaffect each other? How do objects with thesame charge affect each other?

Rub ALL parts of your balloonagain. Hold it by the string.Slowly bring it near theballoon of another group.Observe.

Hold your balloon by thestring. Hold your cloth aboutan arms length away.Gradually bring them closertogether. Observe .

wool cloth

balloon and string

safety goggles

Rubbing causes your balloonto have a negative chargeand your cloth to have apositive charge.

Rub ALL parts

of your balloon!

The effect youobserve is caused bystatic electricity.

The balloon has anegative charge.

The cloth hasa positivecharge.

Both balloons have anegative charge.


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373

Cause and EffectLearning to findcauses and effects can help youunderstand what you read. A cause may have more than oneeffect. An effect may have more than one cause. Words such

as because, so, and as a result may signal cause and effect.Sometimes you can infer cause and effect based on whatyouve observed.

Causes and effects are marked in the advertisement below.

Magazine Advertisement

This new spray tames static electricity. Spray it on socks beforeputting them in the dryer. They wont stick to your shirts. Your hairwill no longer stand up when you remove your winter hat. Usingour patented anti-cling technology, ELECTRO-NOT neutralizes thecharges that build up on your clothing. Let the sparks fly in yourcampfire, not on your clothes. Buy ELECTRO-NOT today. Your sockswill be glad you did!

Apply It!Use the causes andeffects and inferences you can make fromthe advertisement tocomplete a graphic

organizer.

Cause Effect


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ZZZAPP! A jagged bolt of lightning slashesand flashes through the sky. Less than asecond later, its gone. But then more and

more brilliant bolts appear, briefly connectingthe clouds to the ground. Like snowflakesand grains of sand, each bolt is unique.BOOOOM!! The sound of thunder startles you.You are glad that you are indoors, watchingthis dazzling spark-a-palooza through awindow. What causes this beautiful, super-charged sight that can pack a deadly wallop?

374


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375

Lesson 1

How does matterbecome charged?What causes a thundercloud to make lightning? Why do sockscling in the dryer? The answer is static electricity.

Electric ChargesYou dash across a carpet and touch a metal doorknob.

OUCH! A jolt of static electricity and a small spark startle you.

To understand what happened, start with atoms, the tinybuilding blocks of everything. A sheet of paper is about onemillion atoms thick. Almost all atoms have three differentparticles. Some particles have a positive charge (+), some havea negative charge (), and some have no charge. Matter usuallyhas the same number of positive particles as negative particles.It is neutral.

Charged particles can move between objects that are closeto each other. Static electricity happens when positiveand negative charges no longer balance. Static means notmoving, but eventually the static electricity does move. It maymove gradually or it may move very quickly. Moving chargesgenerate electrical energy, which changes into sound, light,and heat energy.

Static Electricity As charged particles move between atoms in storm clouds,

the clouds become charged. Usually, the positive particlescluster near the top and the negative particles gather near thebottom of the clouds. In time, this static electrical energy isreleased as lightning. It heats up the surrounding air, makingit glow. Lightning also creates a mighty soundthunder.

1. What causes static electricity on an object? 2. Benjamin Franklin invented the

lightning rod. Use the Internet or other resources to find outwhat a lightning rod does.


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How Charged Objects BehaveYou can predict how charged objects will behave. If two

objects have opposite chargesif one is positive and theother is negativethey will pull toward each other. Thisattraction causes an electric force. An electric force is thepull or push between objects that have a different charge.

A charged object can attract something that has nocharge. If you rub a balloon on your hair, it picks upnegative particles. It becomes negatively charged.Then, if you hold the balloon near lightweightneutral objects, such as scraps of paper, theymove toward it. The balloon will stick to a wall

because the negative charge repels the negativecharges in the wall. The part of the wall nearthe balloon is positively charged. After awhile, the balloon loses its charge and fallsoff the wall.

Suppose you are wearing a wool cap ona chilly winter day. While you wear thecap, negative particles move from your

hair to the cap. As a result, each strand ofhair becomes positively charged. When youremove the cap, all the positively chargedhairs stand up and move as far away aspossible from the other positively chargedhairs. Two objects that have the same chargepush away, or repel, each other.

The negativelycharged balloonmakes part of thepaper positive. Thatpart of the paper pullstoward the balloon.

Charged amberattracts feathers.

The Name ElectricityMillions of years ago sap oozedfrom a tree trunk. Graduallythe sap hardened. Sometimes ittrapped prehistoric insects. Amberis fossilized tree sap. In Greece, ascientist named Thales noticed thatamber could do amazing tricks.When amber is rubbed on fur, itbecomes charged. Feathers stickto it. The word electricity comesfrom elektron, the Greek wordfor amber.


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377

An Electric FieldThe space around electrically charged objects is called an

electric field. To represent an electric field, scientists drawlines coming out of an object. An electric field is invisible. It

is strongest close to the charged object. It gets weaker fartherfrom the object.

An electric field causes an electric force on charged objectsthat touch it. A positive electric field attracts negative charges.It pushes away positive charges. A negative electric fieldattracts positive charges and pushes away negative ones.

The balloons have oppositecharges. They attract each other.

The balloons have the samecharge. They repel each other.

1. What effect will a charged object have on an object withthe opposite charge?

2. Give two examples of static electricity. 3. Narrative Write a story in your

science journal that tells a curious first grader about static

electricity. Include at least two experiences you might havein a typical day.


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Lesson 2

How do electriccharges ow?

How does the electrical energy in a battery get to a light bulb?To study how electricity moves, scientists build models called circuits.Electric charges travel through different materials at different speeds.

How Electric Charges MoveStatic electricity stays in one place. But most electricity is

on the go. An electric charge in motion is called an electriccurrent. The electric charge flows from one place to another.An electric current travels quickly and invisibly.

Learning how electricity works can be extremely dangerous.Studying a model is a much smarter way to learn how chargestravel. A model of a circuit is shown on the next page. Acircuit is a loop. In order for charges to flow through it, acircuit cannot have any breaks. It must be a closed circuit. In

contrast, an open circuit has at least one break that interruptsthe flow of electric charges. Scientists use symbols to showdifferent parts of the circuit in diagrams. The diagram and thepicture on the next page both show the same circuit.

Going with the Flow The flow of electric charge is not the same in all materials.

Some kinds of atoms become charged more easily than others.Materials made up of such atoms are conductors. The copperwire in the picture and most metals are good conductors. Silveris an excellent conductor of electric charge.

Other materials are made of atoms that do not becomecharged easily. Electric charge moves through them moreslowly. These materials are insulators. Plastic, rubber, glass,and dry wood are good insulators. In the circuit picture, thewire is insulated. This insulation prevents the electric chargesfrom coming in contact with other wires. Different colored

insulations help show how complex circuits with many wiresare connected.

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A ClosedCircuit

Energy sourceBatteries are the power source

for this circuit. They cause theelectric charges to flow.

Means of Energy TransferThe wires provide a path through whichthe charges flow.

SwitchWhen thisswitch isclosed, the

circuit is closed.The electriccharges flowwithout anyinterruptions.

ResistorA coiled wire is inside the light bulb. This wireis made of a material with a high resistance.Resistance means the material does not allowelectric charges to flow through it easily. Because ofthis resistance, the flowing electric charges heat upthe wire. The wire gives off light.

1. What is thedifference between an insulatorand a conductor?

2. Cause and Effect Whatcauses some materials to be goodinsulators of electricity?

Insulated WireThe copper wireis insulated with aplastic covering.


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Types of CircuitsIn a simple circuit, known as a series circuit, electric

charge can flow only in one path. When the power source isturned on, the charged particles in the wire start flowing in

one direction around a single loop. Any bulb along this pathreceives the same amount of electrical energy. If all the bulbsare identical, none will be any brighter than the others.

But, if one bulb burns out, it acts like an off switch andopens the circuit. The other bulbs wont receive the energy theyneed. They wont light either. In a series circuit, all deviceswired into the circuit share the electric current equally. Today,people rarely use series circuits. Our appliances and otherelectrical equipment need different amounts of current.

In a series circuit, one missing

or burnt-out bulb opens thecircuit. No bulbs will light.


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Parallel Circuits

One way to prevent all the lights in a circuitfrom going out is to connect them in a parallelcircuit. A parallel circuit has two or more paths

for the electric charge to follow. The main loopleaves from and returns to the power source. Alongthe loop, however, there are little loops. Each littleloop is a separate path for the electric charge. Howthe charges flow through each little loop does notaffect the flow of charges in any other path.

Circuits in your home, school, and otherbuildings are parallel circuits. A break in one partof the circuit does not stop the charge from flowing.Unlike a series circuit, a parallel circuit can handleelectrical devices that require different amountsof current.

1. What is the main difference between a seriescircuit and a parallel circuit?

2. Why are most homes wired in a parallel circuitrather than a series circuit?

3. Make a drawing of a parallelcircuit that has light bulbs on several little loops.

On one of the little loops, draw the light bulbsconnected in a series circuit.

In a parallelcircuit, a missingor burnt-out bulbdoes not open thecircuit. The otherbulbs stay lit.


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Lesson 3

What aremagnetic elds?

Sometimes magnets pull together, but sometimesthey push apart. What causes magnets and certainother materials to behave this way?

MagnetismA magnet is anything that attracts other

things made of iron, steel, and certain othermetals. Magnetism is a force that actson moving electric charge and magneticmaterials that are near a magnet. Theword magnet comes from Magnesia, apart of ancient Greece that today ispart of Turkey. Long ago, Magnesiawas famous for having large

amounts of lodestone, amagnetic mineral.

Magnetic FieldsHow do magnets work?

Each magnet has aninvisible field around it. Themagnetic field goes out in

all directions. The shape ofthe magnetic field depends onthe shape of the magnet. Look at thepatterns of iron filings near the horseshoemagnet and the bar magnets. The patternsare different because the magnetic fields havedifferent shapes. But whatever the shape of themagnet, the field is strongest at the magnetsends or poles. The pulling or pushing force isstrongest at the poles.

Iron filings near a horsehoemagnet show that the magneticfield is strongest near the poles.


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Magnetic PolesAll magnets have two poles, a north-seeking

and a south-seeking pole. Opposite poles haveopposite charges. Unlike charges attract each

other, while like charges repel each other. So,the north-seeking pole on one magnet and thesouth-seeking pole on another magnet pulltoward each other. But the like poles push apart.

If you break a magnet into two pieces, youwill have two magnets, each with its ownnorth-seeking pole and south-seeking pole. Infact, every magnet has both a north-seekingpole and a south-seeking pole. Think of the twopoles of a magnet like two sides of a coin. Onecannot exist without the other.

Iron filings near abar magnet show themagnetic field is strongestnear the poles.

The north-seeking pole of onebar magnet pulls toward thesouth-seeking pole of anotherbar magnet. The iron filingsshow the magnetic field.

Two north-seeking poles repeleach other. The iron filingsshow the magnetic field.

1. If you breaka magnet into two pieces,what happens to itsmagnetic poles?

2.Use the Internet or otherresources to locate placesother than Magnesia wherelodestone is found.


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The Largest Magnet in the WorldWhy does a compass needle always move to the north-south?

Many ancient sailors used compasses successfully but didntknow why they worked. Christopher Columbus used a compasswhen he crossed the Atlantic. Around 1600, English scientistWilliam Gilbert suggested that the worlds largest magnet isEarth! In other words, he proposed that Earth is a huge magnet,surrounded by an enormous magnetic field.

Earth behaves like a large magnet. Like all magnets, itsmagnetic field is strongest at the poles. But Earths magneticpoles are not located at its geographic poles. Thegeographic poles are on Earths axis, an invisible line

around which our planet rotates. The magnetic northpole is located in Canada, about 1,000 kilometers(600 miles) from the geographic North Pole. Themagnetic south pole is located in the SouthernOcean near Antarctica.

Why does Earth act like a magnet? Scientistsarent sure of the answer. After all, no one hasactually seen the inside of our planet. But based on

indirect evidence, they suggest that Earths outer coreis made of iron that is so hot that it has melted. AsEarth rotates, electric currents that flow in this liquidiron create a magnetic field. The inner core is probablysolid iron that is also very hot. It doesnt melt because ofthe extremely high pressure.

If no magnetis near, thecompassneedlepoints north.

A bar magnetchanges thedirection in

which thecompassneedle points.

How Compasses Work A compass is a helpful, easy-to-

carry tool. Wherever you are on Earth,one end of a compass needle will point tothe North Pole. It follows an imaginary line thatconnects the magnetic poles of Earth. Once youknow which direction is north, you can easilydetermine south, west, and east.

For a compass to work properly, its needlemust be lightweight and turn easily. Thecompass cannot be close to a magnet. Otherwise,the needle will respond to the pull of the magnetrather than to Earths magnetic field.


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The Northern LightsAt certain times of the year, sky-watchers see a spectacular lightshow called the Aurora Borealis, or the Northern Lights. Aurorasare caused by charged particles traveling quickly from the Sun.The charged particles are attracted to the strongest parts of Earthsmagnetic fieldthe magnetic north and south poles. The particles

collide with gases in Earths atmosphere. Atoms in the gases giveoff the colorful light. Earth is not the only planet with auroras.Astronomers have observed auroras in Jupiters atmosphere.

1. What are some ways that Earth is like a magnet? 2. Why does a compass needle point in a north-south direction? 3. Expository Compasses can be used to

create treasure hunts. Hide a small object. Then write clueson index cards and hide all but the first one. The first clue tells

how to use a compass to find next clue, and so on. Challengea friend to use your directions to find the hidden object.

Earth is like a giantmagnet surrounded bya huge magnetic field.


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When nocurrent flows,all compassespoint north.

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Lesson 4

How is electricitytransformed tomagnetism?

Electricity and magnetism are closely related. Both are theresult of charged particles moving. The combination of these forces,electromagnetism, is very useful in our daily lives.

ElectromagnetsIn 1820, Danish scientist Hans Christian Oersted was showing

how electric current flowed through a wire. He noticed that themagnetic needle on a nearby compass moved each time heturned on the current. The electric current caused a magnetic field.The current caused the compass needle to move. Oersted saw thatthe forces of electricity and magnetism have a lot in common.This connection led to an important inventionthe electromagnet.

The compassneedles lineup with themagnetic fieldcaused bythe flowingcurrent.


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Uses for ElectromagnetsElectromagnets are used in industry to lift

heavy materials. Sometimes the materials are theresources needed for manufacturing. Sometimesthey are waste materials that are being movedso that they can be used in a different way.Electromagnets are also in complex machinesused by doctors and scientists.

You may not realize that electromagnetsare part of many electronic gadgets thatyou use every day. Televisions, fans, VCRs,computers, and DVD players all work because

of electromagnets. In the examples hereadoorbell, a motor, and earphonesyoull seehow electromagnets help convert electric energyto magnetic energy to mechanical energy.

ButtonPressing the buttoncloses the electric circuit.

Current flows to the

TransformerThis devicecontrols the amount of currentthat is sent to the

ElectromagnetElectricityflowing in the coil of wiremagnetizes the electromagnet.This pulls up the

Contact ArmThe armis attached to a metalclapper that hits the

BellThis makesthe sound.

Batterypower source

Simple ElectricMotorA motor uses magnets tocreate motion. A simplemotor has six parts.

How a Doorbell Works


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1. Cause and EffectHow did noticing cause andeffect lead to Hans ChristianOersteds discovery?

2. Why are electromagnets usedin so many electronic devices?

3.Use the Internet or otherresources to find examples of

electromagnets used in industryor medicine.

EARPHONES turn electric current intosound waves. A metal disc is locatedin front of an electromagnet in eachearphone. Changes in the electric currentmake the magnetism weaker or stronger.The changes in magnetic strength makethe disc vibrate. The vibrations are thesound waves you hear.

Armature or Rotora set ofelectromagnets, each with thincopper wire coiled around it

Commutatorswitch that reversesthe direction of the electric current

Brushthe contact point on each side ofthe armature that transfers power when themotor spins

Axleholds the commutatorand the armature

Permanent Magnetworks with theelectromagnets in the armature. The northend of the permanent magnet pushesaway the north end of the electromagnet.The south ends also push away from eachother. This causes the axle to spin.


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Lesson 5

How is magnetismtransformed toelectricity?

The power of magnetism can be transformed into the power ofelectricity. This discovery led to the invention of the electric motor,

generator, and more.

Electrical Energy Most people take electricity for granted. They find it hard

to picture daily life before electricity. They push plugs intooutlets, without thinking about where the electricity comesfrom. They dont realize that the electrical energy thatpowers their televisions, refrigerators, and lamps hastraveled a long way.

Today we know more ways to use magnetism togenerate electricity. Sliding coiled wire back and forthover a magnet generates electricity. Spinning a coiledwire around a magnet produces electricity too.

When a magnet is moved, its magnetic fieldmoves with it. And changing a magnetic fieldgenerates electricity. The faster the coiled wireor the magnet is moved, the stronger theelectric current it produces. In contrast,

the slower the movement, the weakerthe current. The number ofcoiled loops also affectsthe strength of thecurrent. More coiledloops of wire mean themagnet createsa stronger current.

Wires are wound in coils

around magnets. The wires areattached to instruments thatmeasure the electric current.


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A Flashlight Without BatteriesIn 1831, Michael Faraday invented a machine

that used magnets to transform motion into an

electric current. By turning a crank, he was able toproduce electrical energy. He called this inventiona dynamo. Today this technology is used in anemergency flashlight. It does not use batteries.Instead, it produces electricity when the usersqueezes the handle.

Currents Currently Most homes, scho

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