Temperature, Heat, Temperature, Heat, and Expansionand Expansion

Chapter 21Chapter 21

TemperatureTemperature Temperature – Temperature – the quantity that tells how hot the quantity that tells how hot

or cold something is compared with a standardor cold something is compared with a standard A common thermometer measures A common thermometer measures

temperature by showing the expansion and temperature by showing the expansion and contraction of a liquid in a glass tube using a contraction of a liquid in a glass tube using a scalescale

Celsius Scale – Celsius Scale – most widely used most widely used temperature scale, 0ºC is the point at which temperature scale, 0ºC is the point at which water freezes and 100ºC the point at which water freezes and 100ºC the point at which water boils, the gap between is divided into water boils, the gap between is divided into 100 equal parts100 equal parts

TemperatureTemperature

Fahrenheit Scale – Fahrenheit Scale – commonly used commonly used in the U.S., has 180ºF between in the U.S., has 180ºF between freezing and boiling (32ºF and 212º)freezing and boiling (32ºF and 212º)

Kelvin Scale – Kelvin Scale – used in scientific used in scientific research, degrees are the same size research, degrees are the same size as Celsius + 273º, denoted Kas Celsius + 273º, denoted K

Absolute Zero – Absolute Zero – the lowest possible the lowest possible temperature on the Kelvin scale, temperature on the Kelvin scale, substance has no kinetic energysubstance has no kinetic energy

ThermometersThermometers

Scale ComparisonScale Comparison

Temperature and Kinetic Temperature and Kinetic EnergyEnergy

In an ideal gas, temperature is In an ideal gas, temperature is proportional to the proportional to the averageaverage kinetic kinetic energyenergy

The heat that you feel when you touch The heat that you feel when you touch a hot surface is the kinetic energy a hot surface is the kinetic energy transferred by molecules in the surface transferred by molecules in the surface to molecules in your fingersto molecules in your fingers

Temperature is Temperature is notnot a measure of the a measure of the totaltotal kinetic energy kinetic energy

HeatHeat Heat – Heat – the energy that transfers from one the energy that transfers from one

object to another because of a temperature object to another because of a temperature difference between themdifference between them

Matter does not contain heat, but contains Matter does not contain heat, but contains energy in several formsenergy in several forms

Heat is energy in transitHeat is energy in transit Internal Energy –Internal Energy – the energy resulting from the energy resulting from

heat flowheat flow When heat flows from one object or When heat flows from one object or

substance to another it is in contact with, the substance to another it is in contact with, the objects are said to be in objects are said to be in thermal contactthermal contact

Heat flows from the higher-temperature Heat flows from the higher-temperature substance into the lower-temperature substance into the lower-temperature substancesubstance

Heat Flow Between Two Heat Flow Between Two GasesGases

Thermal EquilibriumThermal Equilibrium

Thermal Equilibrium – Thermal Equilibrium – objects in objects in thermal contactthermal contact with each other with each other reach the same temperature, no heat reach the same temperature, no heat flows between themflows between them

When reading a thermometer, we When reading a thermometer, we wait until the thermometer has wait until the thermometer has reached reached thermal equilibriumthermal equilibrium with the with the object we want the temperature ofobject we want the temperature of

Thermal EquilibriumThermal Equilibrium

Internal EnergyInternal Energy

Internal Energy – Internal Energy – the total of all the total of all energies inside a substanceenergies inside a substance

A substance does not contain heat – A substance does not contain heat – it contains it contains internal energyinternal energy

When a substance takes in or gives When a substance takes in or gives off heat, any of these energies can off heat, any of these energies can changechange

Internal EnergyInternal Energy

Measurement of HeatMeasurement of Heat To quantify heat, we have to specify the mass To quantify heat, we have to specify the mass

and kind of substance affectedand kind of substance affected Calorie – Calorie – the most commonly used unit for the most commonly used unit for

heat; the amount of heat required to raise the heat; the amount of heat required to raise the temperature of 1 gram of water by 1temperature of 1 gram of water by 1ºCºC

Kilocalorie – Kilocalorie – the heat required to raise 1 the heat required to raise 1 kilogram of water by 1ºC (1000 kilogram of water by 1ºC (1000 caloriescalories))

The heat unit for rating foods is actually the The heat unit for rating foods is actually the kilocaloriekilocalorie (to distinguish from calorie, it is (to distinguish from calorie, it is often written as Calorie)often written as Calorie)

Remember that a calorie is a measure of Remember that a calorie is a measure of ENERGY!ENERGY!

The relationship between calories and joules is:The relationship between calories and joules is:1 calorie = 4.184 Joules1 calorie = 4.184 Joules

CaloriesCalories

Specific Heat CapacitySpecific Heat Capacity Different substances have different capacities Different substances have different capacities

for storing internal energyfor storing internal energy We find that specific materials require specific We find that specific materials require specific

quantities of heat to raise the temperature of quantities of heat to raise the temperature of a given mass of the material by a specified a given mass of the material by a specified number of degreesnumber of degrees

Specific Heat Capacity – Specific Heat Capacity – the quantity of the quantity of heat required to raise the temperature of a heat required to raise the temperature of a unit mass of a substance by 1unit mass of a substance by 1ºCºC

Q = mcQ = mcΔΔTTQ = quantity of heat; m = mass of substance; Q = quantity of heat; m = mass of substance;

c = specific heat capacity of substance; c = specific heat capacity of substance; ΔΔT = change in temperatureT = change in temperature

We can think of specific heat capacity as We can think of specific heat capacity as thermal inertia (an object’s resistance to thermal inertia (an object’s resistance to change)change)

Specific Heat CapacitiesSpecific Heat Capacities

Thermal ExpansionThermal Expansion

When the temperature of a substance When the temperature of a substance increases, the molecules “jiggle” faster and increases, the molecules “jiggle” faster and move further apart, causing an move further apart, causing an expansionexpansion of the of the substancesubstance

Gases generally expand and contract more than Gases generally expand and contract more than liquids, which expand and contract more than liquids, which expand and contract more than solidssolids

In concrete sidewalks and highways this In concrete sidewalks and highways this expansion and contraction is taken into account expansion and contraction is taken into account when it is being built. The surface is laid down when it is being built. The surface is laid down in small sections with a gap in between, that is in small sections with a gap in between, that is usually filled with a substance such as tar.usually filled with a substance such as tar.

Thermal ExpansionThermal Expansion

Expansion Joint

Expansion of WaterExpansion of Water

Almost all liquids will expand when Almost all liquids will expand when they are heated, ice-cold water instead they are heated, ice-cold water instead contracts to go from ice to a liquidcontracts to go from ice to a liquid

When the water reaches a When the water reaches a temperature of 4temperature of 4ºC, it will stop ºC, it will stop contracting and begin expandingcontracting and begin expanding

This has to do with the crystal This has to do with the crystal structure of water, its solid state has structure of water, its solid state has an open structure that takes up more an open structure that takes up more volume and is therefore less densevolume and is therefore less dense

Expansion of WaterExpansion of Water

Heat TransferHeat Transfer

Chapter 22Chapter 22

ConductionConduction Conduction –Conduction – energy transfer from particle to energy transfer from particle to

particle within certain materials, or from one particle within certain materials, or from one material to another when the two are in direct material to another when the two are in direct contactcontact

Conductors –Conductors – materials that conduct heat well materials that conduct heat well Metals are the best conductors (silver, copper, Metals are the best conductors (silver, copper,

aluminum, and iron)aluminum, and iron) Materials composed if atoms with “loose” outer Materials composed if atoms with “loose” outer

electrons are good conductors of heatelectrons are good conductors of heat Insulators –Insulators – materials which delay the transfer materials which delay the transfer

of heat (wood, wool, straw, paper, cork, and of heat (wood, wool, straw, paper, cork, and Styrofoam)Styrofoam)

Cold is simply the absence of heat, only heat is Cold is simply the absence of heat, only heat is transferred through a conductor or insulatortransferred through a conductor or insulator

ConvectionConvection

Convection –Convection – a means of heat transfer a means of heat transfer by movement of the heated substance by movement of the heated substance itself, such as by currents in a fluiditself, such as by currents in a fluid

Convection occurs in all fluids, whether Convection occurs in all fluids, whether liquid or gasliquid or gas

Convection is occurring all around you, Convection is occurring all around you, the atmosphere, the ocean, Earth, the the atmosphere, the ocean, Earth, the sun!sun!

As warm air rises, it expands and coolsAs warm air rises, it expands and cools When the air has been cooled, it will When the air has been cooled, it will

sink back down again and warm up …sink back down again and warm up …

ConvectionConvection

RadiationRadiation

Radiation –Radiation – Energy transmitted by Energy transmitted by electromagnetic waves (i.e. the sun)electromagnetic waves (i.e. the sun)

Radiant Energy –Radiant Energy – any energy, any energy, including heat, that is transmitted by including heat, that is transmitted by radiationradiation

All objects continually emit radiant All objects continually emit radiant energy in a mixture of wavelengthsenergy in a mixture of wavelengths

The lower the temperature, the longer The lower the temperature, the longer the wavelengththe wavelength

Three Mechanisms of Heat Three Mechanisms of Heat TransferTransfer

Absorption of Radiant Absorption of Radiant EnergyEnergy

Absorption and reflection are Absorption and reflection are opposite processes, a good absorber opposite processes, a good absorber of radiant energy will reflect only a of radiant energy will reflect only a little amount of radiant energylittle amount of radiant energy

A perfect absorber will reflect no A perfect absorber will reflect no radiant energy and appear blackradiant energy and appear black

Good reflectors are poor absorbers of Good reflectors are poor absorbers of radiant energyradiant energy

Emission of Radiant EnergyEmission of Radiant Energy

Good absorbers are also good Good absorbers are also good emitters; poor absorbers are poor emitters; poor absorbers are poor emittersemitters

If a good absorber was not also a If a good absorber was not also a good emitter, then black objects good emitter, then black objects would remain warmer than lighter would remain warmer than lighter colored objects and never come to colored objects and never come to thermal equilibrium with themthermal equilibrium with them

Each object is emitting as much Each object is emitting as much energy as it is absorbingenergy as it is absorbing

Absorption and Emission of Absorption and Emission of Radiant EnergyRadiant Energy

Newton’s Law of CoolingNewton’s Law of Cooling The rate of cooling of an object depends on The rate of cooling of an object depends on

how much hotter the object is than the how much hotter the object is than the surroundingssurroundings

The rate of cooling of an object – whether The rate of cooling of an object – whether by conduction, convection, or radiation – by conduction, convection, or radiation –

is approximately proportional to the is approximately proportional to the temperature difference temperature difference ΔΔT T between the between the

object and its surroundingsobject and its surroundings

Rate of cooling ~ Rate of cooling ~ ΔΔTT

Newton’s law of cooling also holds for heatingNewton’s law of cooling also holds for heating

Global WarmingGlobal Warming Greenhouse Effect – Greenhouse Effect – The warming effect The warming effect

whose cause is that short-wavelength whose cause is that short-wavelength radiant energy from the sun can enter the radiant energy from the sun can enter the atmosphere and be absorbed by Earth atmosphere and be absorbed by Earth more easily than long-wavelength energy more easily than long-wavelength energy from Earth can leavefrom Earth can leave

Earth absorbs the energy from the sun Earth absorbs the energy from the sun through the atmospherethrough the atmosphere

As the atmosphere gets thicker from carbon As the atmosphere gets thicker from carbon dioxide, it will not allow as much energy to dioxide, it will not allow as much energy to escape into spaceescape into space

Terrestrial Radiation –Terrestrial Radiation – Energy that Earth Energy that Earth radiatesradiates

The Greenhouse EffectThe Greenhouse Effect

AssignmentAssignment

Read Chapters 21 & 22 (pg. 307-336)Read Chapters 21 & 22 (pg. 307-336) Do Chapter 21 #25-48 (pg. 323-324); Do Chapter 21 #25-48 (pg. 323-324);

Appendix F #1-7 (pg. 680)Appendix F #1-7 (pg. 680) Do Chapter 22 #21-30 (pg. 338)Do Chapter 22 #21-30 (pg. 338)