Thermal Energy Thermal Energy & Heat& Heat

Physical SciencePhysical ScienceChapter 16Chapter 16

Thermal Energy

Sometimes called internal energy

Depends on the object's mass, temperature, and phase (solid, liquid, gas)

TOTAL potential and kinetic energy of all the particles in an object

Heat vs. TemperatureHeatHeat

The The spontaneous spontaneous flow flow of THERMAL energy of THERMAL energy from a hot object to a from a hot object to a cold objectcold object

Change in EnergyChange in Energy

Temperature a measure of how hot or

cold an object is compared to a reference point

A measure of the AVERAGE kinetic energy of the particles in an object

Temp, Thermal Energy, & HeatTemp, Thermal Energy, & Heat TemperaturTemperaturee – a measure of the AVERAGE – a measure of the AVERAGE

kinetic energy of the individual particles of kinetic energy of the individual particles of a substance.a substance.

Thermal energy Thermal energy – TOTAL energy of all of – TOTAL energy of all of the particlesthe particles

HeatHeat – THERMAL energy moving from a – THERMAL energy moving from a warmer object to a cooler object, trying to warmer object to a cooler object, trying to reach thermodynamic equilibrium. reach thermodynamic equilibrium.

Thermal energy vs. temp

Now remember that thermal energy, unlike temperature, depends on mass

Compare a cup of tea and a teapot full of tea, both at the same temperature– Is the average kinetic energy the same in

both? YES! (that’s why they have the same

temperature)

– Which has more thermal energy and why? The teapot because it has more particles (mass)!

Thermal energy varies with temperature

Compare a cup of hot tea with a cup of cold tea– Assume each cup is the same size and has

the same mass – Does each cup have the same amount of

particles? Yes

– Which has the higher average kinetic energy? Hot tea

– So, which has the greater thermal energy? Hot tea

Thermal energy

Which has more thermal energy?– Pitcher of cool lemonade or cup of hot tea?– Pot of boiling water or an iceberg?

Eureka - Temperature vs. heat

So, how do thermometers work?

Thermal expansion and contraction

Particles move faster and expand as they warm

So, as the temperature increases, the alcohol in the tube expands and its height increases

Absolute Zero -459o -273o 0o

Absolute zero- that temperature where the individual particles contain no more energy. The particles (atoms and/or molecules) cease vibrating. No movement occurs.

Warm-up Section 16-1 Warm-up Section 16-1 Review p.478Review p.478

In which direction does heat flow on its own In which direction does heat flow on its own spontaneously?spontaneously?

Name 2 variables that affect the thermal energy Name 2 variables that affect the thermal energy of an object.of an object.

Why is it necessary to have regularly spaced gaps Why is it necessary to have regularly spaced gaps between sections of a concrete sidewalk?between sections of a concrete sidewalk?

Calorimeter

Measures changes in thermal energy

Uses the principle that heat flows from a hotter object to a colder object until both reach the same temperature.

Read p.478 in textbook

ThermodynamicsThermodynamics

Heat TransferHeat Transfer Heat moves in only one direction: from a Heat moves in only one direction: from a

warmer object to a cooler objectwarmer object to a cooler object Two drinks in the same room:Two drinks in the same room:

The hot coffee __________ to room temp The hot coffee __________ to room temp because . . .because . . .

The iced tea _______ to room temp The iced tea _______ to room temp because . . . because . . .

– Hot coffee cools to room temp because Hot coffee cools to room temp because the heat of the coffee is transferred to the heat of the coffee is transferred to the cooler temperature of the room.the cooler temperature of the room.

– A cold glass of Iced tea soon warms up A cold glass of Iced tea soon warms up to the surrounding room temperature to the surrounding room temperature because the warmer temperature of the because the warmer temperature of the room’s surroundings is transferred to room’s surroundings is transferred to the colder glass of iced tea thereby the colder glass of iced tea thereby warming it up.warming it up.

Heat TransferHeat Transfer Heat is transferred in one of three ways:Heat is transferred in one of three ways:

– ConductionConduction– Convection Convection – RadiationRadiation

Specific Heat Video

Heat Transfer TutorialHeat Transfer Tutorial

ConductionConduction ConductionConduction – heat is transferred from – heat is transferred from

one object to another by direct one object to another by direct contact. contact. – Examples include: a metal spoon in Examples include: a metal spoon in

hot water gets hot or a pot gets hot hot water gets hot or a pot gets hot as it sits on an electric stove.as it sits on an electric stove.

– Fastest in solids. Much slower in Fastest in solids. Much slower in gases. Why? (think about gases. Why? (think about collisions)collisions)

Conductors vs. InsulatorsConductors vs. InsulatorsConductorConductor – a material that transfers heat – a material that transfers heat

well: metal, tile, glasswell: metal, tile, glass- high rate of thermal energy - high rate of thermal energy

transfertransfer

InsulatorInsulator – a material that does not – a material that does not transfer heat well: air, carpet, wood, transfer heat well: air, carpet, wood, woolwool

- low rate of thermal energy transfer- low rate of thermal energy transfer

Conductors vs. Insulators animationConductors vs. Insulators animationConductors vs. Insulators activityConductors vs. Insulators activity

Why does a tile floor feel colder than a wood Why does a tile floor feel colder than a wood floor, even though they're both at room floor, even though they're both at room temperature?temperature?

– The tile feels colder because it is a better conductor The tile feels colder because it is a better conductor and transfers thermal energy rapidly away from and transfers thermal energy rapidly away from your skin.your skin.

Conduction in different phases

-Slower in gases than in liquids and solids because there is more space in between molecules

-Dressing in layers to insulate-Gaps of air in layers of blankets, newspapers, etc.

Why does a thick wool sweater keep Why does a thick wool sweater keep you warm?you warm?

Convection Convection ConvectionConvection – the transfer of thermal energy when – the transfer of thermal energy when

particles of a fluid move from one place to particles of a fluid move from one place to another….the particles transfer the heat. another….the particles transfer the heat. – Examples include: a pot of boiling water sets Examples include: a pot of boiling water sets

up convection currents to move the hot water up convection currents to move the hot water at the bottom of the pot being heated to the at the bottom of the pot being heated to the cooler water at the top of the pot, convection cooler water at the top of the pot, convection currents in a heated room keep the currents in a heated room keep the temperature uniform.temperature uniform.

Convection of warm airConvection of warm air

Air is heated by sunlightAir is heated by sunlight The temperature of the airThe temperature of the air

– IncreasesIncreases The air The air

– ExpandsExpands The less dense airThe less dense air

– RisesRises The denser airThe denser air

– SinksSinks

RadiationRadiation Radiation Radiation – transfer of energy by electromagnetic – transfer of energy by electromagnetic

waves. waves. – Examples include: the Sun’s energy traveling Examples include: the Sun’s energy traveling

through space and heating up the Earth w/out through space and heating up the Earth w/out heating space itself, Heat lamps used at fast heating space itself, Heat lamps used at fast food restaurants, and the radiator of a car food restaurants, and the radiator of a car dissipating the heat of an engine.dissipating the heat of an engine.

RadiationRadiation All objects radiate energy: All objects radiate energy:

– a fire, the sun, your bodya fire, the sun, your body

As temp goes up the rate at which it As temp goes up the rate at which it radiates goes upradiates goes up

infrared galleryinfrared gallery

What type of heat transfer What type of heat transfer is represented by each is represented by each

arrow?arrow?

Physical Science Physical Science Hot Body CompetitionHot Body Competition

Rules:Rules: 1. Must hold ice cube in 1 hand and 1. Must hold ice cube in 1 hand and

can't transfer it to the other.can't transfer it to the other. 2. No blowing into hand or rubbing 2. No blowing into hand or rubbing

with other hand.with other hand. 3. If cube is dropped you are out.3. If cube is dropped you are out. 4. You must melt entire cube.4. You must melt entire cube.

Laws of ThermodynamicsLaws of Thermodynamics 11stst Law- energy is conserved Law- energy is conserved 22ndnd Law- heat energy can only go from Law- heat energy can only go from

a cold to a hot object if work is donea cold to a hot object if work is done– RefrigeratorRefrigerator– A heat engine converts heat into workA heat engine converts heat into work– One consequence of the 2One consequence of the 2ndnd law is that law is that

the efficiency of a heat engine is always the efficiency of a heat engine is always less than 100%less than 100% Waste heat must be lost for the heat engine Waste heat must be lost for the heat engine

to work!!!to work!!!

33rdrd Law- absolute zero can’t be Law- absolute zero can’t be reachedreached

Quick Quiz Review Heat vs. Temperature

Thermal Energy

Go over Ch. 16.2 Assessment p.483 #1-10, p.496 #28-30