Thermal EnergyThermal Energy

Chapter 16Chapter 16

TemperatureTemperature – related to the – related to the average kinetic energy of an object’s average kinetic energy of an object’s atoms or molecules, a measure of atoms or molecules, a measure of how hot (or cold) something ishow hot (or cold) something is

Thermal energyThermal energy – the sum of the – the sum of the kinetic and potential energy of all the kinetic and potential energy of all the atoms in an objectatoms in an object– Thermal energy increases as Thermal energy increases as

temperature increasestemperature increases– At constant temperature, thermal At constant temperature, thermal

energy increases if mass increasesenergy increases if mass increases

HeatHeat - thermal energy that flows from - thermal energy that flows from something at a higher temperature to something at a higher temperature to something at a lower temperature something at a lower temperature

Specific heatSpecific heat – amount of heat needed – amount of heat needed to raise the temperature of 1kg of a to raise the temperature of 1kg of a material by 1 degree C or Kmaterial by 1 degree C or K

Specific Heat EquationSpecific Heat Equationenergy = (specific heat) energy = (specific heat) (mass) (mass)

(temperature change) (temperature change)energy = energy = cmcmtt

FahrenheitFahrenheit and and CelsiusCelsius are common are common scales used for measuring temperatures.scales used for measuring temperatures.

On the On the FahrenheitFahrenheit scale, water scale, water freezes at 32ºF and boils at 212ºF. freezes at 32ºF and boils at 212ºF.

• The The CelsiusCelsius scale, which is widely scale, which is widely used in science, gives a value of 0ºC used in science, gives a value of 0ºC to the freezing point of water and a to the freezing point of water and a value of 100ºC to the boiling point of value of 100ºC to the boiling point of water at standard atmospheric water at standard atmospheric pressurepressure

Fahrenheit-Celsius Conversion Fahrenheit-Celsius Conversion EquationsEquations

A degree Celsius is 1.8 times as large as A degree Celsius is 1.8 times as large as a degree Fahrenheit. Also, the a degree Fahrenheit. Also, the temperature at which water freezes temperature at which water freezes differs for the two scales by 32 degrees.differs for the two scales by 32 degrees.

TF 1.8t 32.0 t TF – 32.0

1.8TTFF = Fahrenheit temperature = Fahrenheit temperature tt = Celsius temperature = Celsius temperature

The The KelvinKelvin scale is based on scale is based on absolute zero.absolute zero.

Absolute zeroAbsolute zero is the temperature at is the temperature at which molecular energy is at a which molecular energy is at a minimum (0 K on the Kelvin scale or –minimum (0 K on the Kelvin scale or –273.16ºC on the Celsius scale).273.16ºC on the Celsius scale).

Celsius-Kelvin Conversion EquationCelsius-Kelvin Conversion Equation

TT = = tt + 237 + 237

TT = Kelvin temperature = Kelvin temperaturett = Celsius temperature = Celsius temperature

Changes in thermal energy can be Changes in thermal energy can be calculated as calculated as change in thermal energy change in thermal energy = mass X change in temperature X = mass X change in temperature X specific heatspecific heat– When heat flows into an object and When heat flows into an object and

its temperature rises, the change in its temperature rises, the change in temp is positivetemp is positive

– When heat flows out of an object and When heat flows out of an object and its temperature decreases, the its temperature decreases, the change in temperature is negativechange in temperature is negative

CalorimeterCalorimeter –used to measure specific –used to measure specific heatheat

ConductionConduction – transfer of thermal energy – transfer of thermal energy through matterthrough matter by by direct contactdirect contact of of particlesparticles– Kinetic energy is transferred as Kinetic energy is transferred as

particles collideparticles collide– Solids, particularly metals, are good Solids, particularly metals, are good

heat conductorsheat conductors ConvectionConvection – the transfer of energy by – the transfer of energy by

the motion of heated particles the motion of heated particles in a fluidin a fluid– Transfer heat from warmer to cooler Transfer heat from warmer to cooler

parts in a fluidparts in a fluid– Create rain forests and deserts over Create rain forests and deserts over

different regions of Earthdifferent regions of Earth

RadiationRadiation – energy transfer by – energy transfer by electromagnetic waveselectromagnetic waves– Some radiation is absorbed and some is Some radiation is absorbed and some is

reflected when it strikes a materialreflected when it strikes a material– Heat transfer by radiation is faster in a Heat transfer by radiation is faster in a

gas than in a liquid or solidgas than in a liquid or solid

Most living things control the flow of heat Most living things control the flow of heat by using special features such as fur, by using special features such as fur, blubber, or scalesblubber, or scales

InsulatorInsulator – material that does not let – material that does not let heat flow through it easilyheat flow through it easily– Gases such as air usually make better Gases such as air usually make better

insulators than liquids or solidsinsulators than liquids or solids– A vacuum layer in a thermos is a good A vacuum layer in a thermos is a good

insulator because it contains almost insulator because it contains almost no matter to allow conduction or no matter to allow conduction or convection to occurconvection to occur

conductorconductor Any material through Any material through which energy can be easily which energy can be easily transferred as heattransferred as heat

Poor conductors are called Poor conductors are called insulators.insulators.

• Gases are extremely poor conductors.Gases are extremely poor conductors.

• Liquids are also poor conductors.Liquids are also poor conductors.

• Some solids, such as rubber and wood, Some solids, such as rubber and wood, are good insulators. are good insulators.

• Most metals are good conductors.Most metals are good conductors.

Heating systemsHeating systems – warm homes and – warm homes and buildingbuilding– Forced-air systemForced-air system – fuel heats air, – fuel heats air,

which is blown through ducts and which is blown through ducts and vents; cool air is returned to the vents; cool air is returned to the furnace to be reheatedfurnace to be reheated

– Radiator systemRadiator system – hot water or – hot water or steam in a radiator transfers thermal steam in a radiator transfers thermal energy to the airenergy to the air

– Electric heating systemElectric heating system – – electrically heated coils in ceilings or electrically heated coils in ceilings or floors heat air by conductionfloors heat air by conduction

Solar energySolar energy – – energy from the Sunenergy from the Sun– Passive solar Passive solar

heatingheating - does - does not use not use mechanical mechanical devices to move devices to move heatheat

– Active solar Active solar heatingheating - use - use solar collectors to solar collectors to absorb radiant absorb radiant energy, which is energy, which is circulated through circulated through the buildingthe building

Active Solar Heating System

Heat engineHeat engine – an engine that – an engine that converts thermal energy into converts thermal energy into mechanical energymechanical energy– Internal combustion engineInternal combustion engine – –

burns fuel inside the engine in burns fuel inside the engine in chambers or cylinderschambers or cylinders

– ICE converts only about 26% of the ICE converts only about 26% of the fuel’s chemical energy to fuel’s chemical energy to mechanical energymechanical energy

Internal Combustion EngineInternal Combustion Engine

Machines operate with Machines operate with two energy two energy principles:principles:

The first law of thermodynamicsThe first law of thermodynamics states that the total energy used in any states that the total energy used in any process—whether that energy is process—whether that energy is transferred as a result of work, heat, or transferred as a result of work, heat, or both—is conserved.both—is conserved.

The second law of thermodynamicsThe second law of thermodynamics states that the energy transferred as heat states that the energy transferred as heat always moves from an object at a higher always moves from an object at a higher temperature to an object at a lower temperature to an object at a lower temperature.temperature.

Air ConditionerAir Conditioner

One example is an air conditioner. An air conditioner does work to remove energy as heat from the warm air inside a room and then transfers the energy to the warmer air outside the room.

Passive Solar HeatingPassive Solar Heating