THERMAL EXPANSIONTHERMAL EXPANSION

Linear ExpansionArea Expansion

Volume Expansion

THE FIVE CHANGES IN PHASETHE FIVE CHANGES IN PHASE

Why do highways seem so bumpy in summer or winter?

Why are there gaps in the sidewalk every few feet?

Why does a pan full of water overflow when it is heated?

What are the teeth-like things in the road or bridges?

Expansion of train tracks

Cracks appeared on roads due to expansion

Concepts on Thermal ExpansionConcepts on Thermal Expansion

Heat

Temperature

Thermal Energy

Internal Energy

HeatHeatThe transfer of energy due to difference in

temperature.

Thermal EnergyThermal EnergyThe total kinetic energy due to the random

motion of all the molecules in a substance.

OH

H

H2O molecule

Thermal EnergyThermal EnergyThe total kinetic energy due to random

motion of molecules.

O

H

H

OH

H

OH

H

Translational

Vibratory

Rotational

TemperatureTemperatureDegree of hotness or coldness of a body.Indicator of average kinetic energy of the

molecules of a substance.

Thermometric ScalesThermometric ScalesCelsius ScaleFahrenheit ScaleKelvin ScaleRankine Scale

The glass of water and the sea may have the same temperature but they have different thermal energy.

Sea at 30 ° C Glass of Water at 30 ° C

Internal EnergyInternal EnergyThe total kinetic energy (thermal energy)

and the potential energy resulting from the bonds and interactions of the particles with each other.

OH

H

OH

HO

H

H

OH

H

O

H

H

OH

H

OH

HO

H

H

Activity on Thermal ExpansionActivity on Thermal Expansion

Materials Needed:Wire (1 m or 1 yd. Long)Large nail or small boltHeat source or candleMatchIron Stand

Caution: This activity uses open flame, close Caution: This activity uses open flame, close supervision is needed.supervision is needed.

What happens to solids as they are What happens to solids as they are heated and cooled?heated and cooled?

Procedure:Procedure:1. Wrap one end of the wire around the nail/bolt

and anchor the other end to the iron stand. 2. The nail/bolt should swing freely but barely

misses the floor.3. Heat the wire using the candle or any heat

source.4.Observe the nail/bolt. What happened?5.Remove the heat source and allow the wire to

cool.6. Observe the nail/bolt. What happened?7. What can you say about the effects of heat

on solids

As the wire is heated, it will expand and the nail/bolt, which was swinging freely above the surface, will drag. As it cools, the wire will contract and the nail will swing freely again.

Other solids expand and contract similarly when heated and cooled.

What happens to solids as they are What happens to solids as they are heated and cooled?heated and cooled?

Linear ExpansionLinear Expansion

ΔL α ΔT and ΔL α Lo

Linear ExpansionLinear ExpansionΔL α ΔT and ΔL α Loso, ΔL α LoΔTthen, ΔL = kLoΔT

* ΔL = αLoΔTwhere, ΔL change in length

α coefficient of linear expansionLo original lengthΔT change in temperature

* ΔL = αLoΔTΔL = L – LoL = Lo + ΔL

* L = Lo + αLoΔT* L = Lo (1 + αLΔT)

Linear ExpansionLinear Expansion

Area ExpansionArea ExpansionΔA = 2αAoΔTA = Ao + 2αAoΔTA = Ao (1 + 2αΔT)

Volume ExpansionVolume ExpansionΔV = 3αVoΔT

V = Vo + 3αVoΔT or V = Vo + βVoΔT

V = Vo (1 + 3αΔT) or V = Vo (1 + βΔT)

where β is the coefficient of volume expansion

Coefficients of Linear Expansion Coefficients of Linear Expansion αα

Material α ( x10-5/C° )Aluminum 2.4Brass 2.0Copper 1.7Glass 0.4 to 0.9Quartz 0.04Steel 1.2

β ( x10-5/C° )Aluminum 7.2Brass 6.0Copper 5.1

Glass 1.2 to 2.7Invar 0.27Quartz 0.12Steel 3.6Ethanol 75Carbon disulfide 115Glycerin 49Mercury 18

Coefficients of Volume Expansion Coefficients of Volume Expansion β

Other examples of Thermal ExpansionOther examples of Thermal Expansion

As the iron rod is heated, it lengthens and breaks a glass rod that's put through a hole in the rod.

Thermal Expansion of AirThermal Expansion of Air

Before cooling After cooling

Eiffel TowerEiffel Tower

Did you know that because of thermal expansion the Eiffel Tower is 15cm taller in summer?

Problem Solving on Thermal Problem Solving on Thermal ExpansionExpansion

1. A 5 cm steel rod is heated. How much does it expand when its temperature rises from 20°C to 40°C?

2.Your house contains 453m3 of air at night(20°C). What volume of air leaves the house through an open window if the air warms to 40°C?

3. A glass flask with volume of 200cm3 is completely filled with mercury at 20°C. How much mercury overflows when the temperature raised to 100 °C?

EvaluationEvaluationWhy should the material that the dentists use

for filling have the same thermal expansion properties as your teeth?

Why are some bridges only Why are some bridges only anchored on one end?  (The other anchored on one end?  (The other

end just rests on the pillarend just rests on the pillar

AgreementAgreement

1. If you know an auto mobile mechanic, ask him why wheel bearings are sometimes installed on axles when they are hot?

2. What are the Laws of Thermodynamics?