TOPIC 4 Expansion and Contraction - Basic Knowledge 101

1 210 MHR Heat and TemperatureTOPIC4 Expansion and Contraction As materials warm up, the particle model of matter says that their particles move faster and spread apart. We expect substances to expand(increase in volume) as their temperature rises. Falling temperaturemeans that average particle motion is slowing down. It seems logical toexpect substances to contract(decrease in volume) as they can check those predictions by observing the behaviour of common pure substances. A pure substance is a type of matter that ismade of only one kind of particle. On Earth, a pure substance mayexist as a solid, liquid, or gas. These are the three states or phases ofmatter. Gold, oxygen, and water are examples of pure the illustrations to review the key characteristics of each three states of matterIn the solid state, materials keep their shape and size. Solids like icehave a definite shape and volume and cannot be compressed into asmaller space.

2 In the liquid state, materials have a definite size (volume),but no fixed shape. Liquids like water settle to the bottom of their container and take its shape. Liquids cannot be compressed. Gaseshave no definite shape or volume. They expand to fill all parts of theircontainer and can easily be compressed into a smaller space. Many gases cannot be seen. For example, the space just above a kettle s spoutis filled with invisible water vapour (steam). As the water vapour (waterin the gaseous state) rises and cools, it forms a cloud of tiny drops ofliquid everything weobserve has the proper-ties of matter. Light doesnot take up space or havemass; neither doessound. When you turn ona lamp or stereo, and filla room with light orsound, the room doesnot become and sound areforms of energy, and likeall forms of energy, theydo not have mass or vol-ume. With this in mind,make a prediction aboutwhether the mass of anobject changes when itwarms or cools (that is,when its thermal energychanges).

3 Write some ideas toanswer the questionsbelow. Do not worryabout being correct. You can change yourideas as you workthrough this TOPIC .(a)Are the ice, liquidwater, and watervapour in the illustra-tions made of thesame kind of particle,or are they differenttypes of matter?(b)How does the motionof particles in solids,liquids, and gasesdiffer? Expansion and Contraction MHR 211 Expansion and Contraction of SolidsThe lengths of solid bars of differentmaterials can be measured at differenttemperatures using very precise equip-ment. Table 1 shows some of thesemeasurements. You can see that thechanges in a 100 cm long bar are verysmall. If the bar were twice as long,however, the changes would be twice aslarge. In a very long structure, such as abridge or a train track, the small changescan add up and become very OutStretch and ShrinkAre there similarities in how substancesexpand when heated? Are there similarities inhow they behave when cooled?

4 This activitywill help you to identify any Table 1 above, and use it toanswer these questions.(a)What similarity do you see in how allthe materials react as they warm? (b)In what way do the materials react differently as they warm?(c)Which material expands the most as it warms?(d)Which material expands the least as it warms? the list of materials in Table 1, butarrange them in order, starting with the material that expands the most and endingwith the one that expands the Did You Find Out? do you notice about your list whenyou examine how the materials cool andcontract? Does the material that expandsthe most at a high temperature also contract the most at a low temperature?2. ApplyA baker places a paper cone intothe centre of a fruit pie before putting thepie in the oven. Explain why this wouldkeep juice from running out of the pie during and InterpretingPerforming and RecordingLength at 100 C(cm)Length at 0 C(cm)Length at 100 C(cm)Materialleadsteelaluminumbrasscoppe rglassPyrex 1 Expansion and Contraction of to GrowCivil engineers have to think about thermal Expansion and Contraction when planning roadways, sidewalks, and that a builder or a civil engineer has been invited to speak to your class.

5 Writefive questions that you would like to ask this person about engineering as a sure that your questions are clearly worded, and that they will help you find outwhat you want to Heat and TemperatureExpanding SolidsWhen substances are heated and cooled, changes in size can be small and easy to overlook. Make a prediction and then check it in this Precautions You will be working with an openflame and hot objects. Be careful!Apparatuslong copper or iron wiresmall hooked mass (200 g or 500 g)metre stickball-and-ring apparatuslaboratory burner2 lab stands2 C clampsMaterialscandles, matches, cold waterPart 1 The Sagging WireProcedureStudy the procedure stepsbelow. Then use yourhypothesis to write a spe-cific prediction. What willhappen to the weight as thewire warms and cools? Clamp two supports firmlyto the table and stretch thewire tightly between the small mass in themiddle of the wire. Put themetre stick behind the mass,and recordits lighted candles to warmthe entire length of the wirefor several minutes.

6 Observeand carefully recordtheheight of the mass after each30 s of warming the recordwhathappens to the height of the mass during the next 2 or 3 (a)If the wire sags, the mass moves down. Does this meanthat the wire is getting longer or shorter? (b)What is happening to the length of the wire if the massmoves up? you observewhat you predicted would happen? your observations support your hypothesis?QuestionWhat evidence can you observeof solid materials expanding asthey are warmed, and contract-ing as they are cooled?HypothesisComplete the followinghypothesis theory suggests that(a)when a material is heatedit will ..(b)when a material is cooled it will ..SKILLCHECKI nitiating and PlanningPerforming and RecordingAnalyzing and InterpretingCommunication and TeamworkFor tips on making predictions, turnto Skill Focus and Contraction MHR 213 Part 2 Your teacher will do the heating in Part 2 as a Ball and RingProcedureObservewhether the brassball fits through the brassring when both the ball and the ring are at the procedure stepsthat follow.

7 Then use yourhypothesis to write aspecific prediction. Howwill heating change whetherthe ball fits through the ring?Observewhether the ballfits through the ring whenyour teacher warms only thering in a hot flame for 30 happenswhen your teacher warmsboth the ring and the a class, brainstorm possible ways to make theball fit through the ring. You or your teacher will testthe ideas until one methodworks. With the ballthrough the ring, cool boththe ball and ring. Try to pullthe ball back through thering. If you cannot, find away to separate them bywarming or did the demonstration give evidencethat solids can expand? Describe what yourteacher did to cause the Expansion and whichpart of the apparatus (the ball, the ring, orboth) did the demonstration give evidencethat solids can contract? Describe what youdid to cause the Contraction and which partof the apparatus (the ball, the ring, or both) well did your hypothesis help you predict the behaviour of the ball and ring?

8 Was it a useful hypothesis, or would you like to modify it? the particle model to explainwhyobjects expand and contract when page 210 for and Apply5. Predicthow the position of the electric transmission lines in the photograph below,taken in summer, would change as the temperature dropped in winter. Why wouldit be a bad idea to stretch the transmissionlines more tightly between the towers so theywould sag less in the summer?214 MHR Heat and TemperatureExpansion and Contraction in GasesBecause most common gases are colourless, they are difficult toobserve. As well, gases have no fixed shape or size. (Remember thatthey always take the shape and size of their container.) If you put gasesin a flexible container such as a balloon, however, you can see that theyexpand and contract much more than solids when the temperaturechanges. Warming a sample of helium from 0 C to 100 C, for example,increases its volume by about one third.

9 Unlike the particles in solids,the particles in gases are far apart and moving fast and freely. Figure particle model predicts that warming air will cause its particles to move faster and spread farther apart. When the air in the flask is warmed, the air expands and fills the are familiar withthree states of is a fourth state of matter, called plasma. To change a material into a plasma, extremely hightemperatures are required, like those insidethe Sun millions of degrees Celsius! In a plasma, individual particles that make upthe material start to break apart into tinierpieces called electrons and ions. Plasmascan be produced on Earth, but only underextreme conditions. Matter on Earth existsas a solid, liquid, or gas almost all of the have observed gasesexpanding, in your workin this unit and in every-day life. Think about thesituations below, andanswer the questions inyour Science Log.(a)A spray can, evenwhen it is almostempty, contains com-pressed gases.

10 Whydoes the safety warn-ing on the label tellyou not to dispose ofthe can by putting itin a fire?(b)The tires on a car arefilled with com-pressed air. In thewinter, when the airtemperature dropsvery low, the tiresbecome slightly flat,even when they arenot leaking. Why? Expansion and Contraction MHR 215 Expansion and Contraction in LiquidsImagine watching a laboratory thermometer as itstemperature changes. As the thermometer liquidmoves up the glass tubing (the bore), it takes upmore space. In other words, the liquid expands as it warms. As the thermometer cools, the liquid contracts, so it moves back down the tubing. The liquid must be contracting as it cools. Do all liquidsexpand and contract in this way? Do some liquidschange volume more than others as they warm andcool? Follow the next activity carefully to find OutBulging BalloonsIn science, even ideas that seem like commonsense are checked to see if they agree withobservations and the rules for logical you find evidence to support the followingstatement, which you read earlier in this TOPIC ?