Thermal Physics

3 key terms

Heat – Energy in transit. The energy transferred between objects because of a difference in temperature.

Temperature – A measure of the average Kinetic Energy of the particles in a substance.

Internal Energy – The energy of a substance due to the random motions of its component particles and the equal to the total energy of those particles.

TemperatureTemperatureWe often associate We often associate

temperature with how hot or temperature with how hot or cold something feelscold something feels

Hot and Cold are terms that Hot and Cold are terms that can be misleadingcan be misleading

The same object can feel warm The same object can feel warm or cool depending on the or cool depending on the properties of the object and the properties of the object and the condition of your bodycondition of your body

HotHot ColdCold Luke warmLuke warm

Moving Energy Moving Energy Changes Temp. Changes Temp. HeatHeat

Consider an oven- turn Consider an oven- turn the dial on and heat is the dial on and heat is delivered as energy delivered as energy flows. When the dial is flows. When the dial is off, energy stops flowing off, energy stops flowing and temperature coolsand temperature cools

TemperatureTemperatureTemperature is proportional to the Temperature is proportional to the

Kinetic Energy of atoms and Kinetic Energy of atoms and molecules.molecules.

To understand temperature, think of To understand temperature, think of atoms & molecules and how they atoms & molecules and how they move. With more heat, atoms move move. With more heat, atoms move more, have more KE. When heat is more, have more KE. When heat is removed, the energy of theses moving removed, the energy of theses moving atoms/ molecules is called internal atoms/ molecules is called internal energy.energy.

Internal EnergyInternal Energy

The energy of substance The energy of substance due to the random due to the random motions of its motions of its component particles and component particles and equal to the total energy equal to the total energy of those particlesof those particles

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Why does a 1200oC sparkle not hurt you, but a 200oC stove burner will give you a nasty burn?

A plasma torch in a welding shop has temperatures hotter than the Sun’s surface, why aren’t welders vaporized?

What has more energy; a cup of boiling hot water or Lake Conroe in the winter time?

Thermal EquilibriumThermal Equilibrium

The state in which two The state in which two bodies in physical contact bodies in physical contact with each other have with each other have identical temperaturesidentical temperatures

COLD COLD WATERWATER

Warm Warm BeveragBeverag

ee

In time both In time both liquids will have liquids will have

equal equal temperaturestemperatures

You can not find temperature until You can not find temperature until thermal equilibrium is reachedthermal equilibrium is reached

The temperature of the liquid in the The temperature of the liquid in the thermometer must balance the thermometer must balance the temperature of the object being temperature of the object being measured. This must happen in measured. This must happen in order to know the temperatureorder to know the temperature

““You don’t read a thermometer You don’t read a thermometer until the mercury/ alcohol has until the mercury/ alcohol has stopped rising/ falling”stopped rising/ falling”

Thermal ExpansionThermal ExpansionThings get Things get HOTHOT they they EXPANDEXPANDThings get Things get COLDCOLD they they CONTRACTCONTRACT

– Concrete bridgesConcrete bridges– Rail Road RailsRail Road Rails– Power LinesPower Lines– Hot glass – cold water – cracksHot glass – cold water – cracks

This is True for all solids, liquids This is True for all solids, liquids and gasses (some more than and gasses (some more than others)others)

Anomaly of WaterAnomaly of Water

A strange thing A strange thing happens to water happens to water between 0°- between 0°- 4°C: as it gets colder, 4°C: as it gets colder, it EXPANDS- it EXPANDS- GOOD NEWS FOR GOOD NEWS FOR FISH!!FISH!!

ICE 0ICE 0°°CC

11°°22°°

33°°

44°°

ThermometersThermometersA glass tube containing a A glass tube containing a

thin column of mercury, thin column of mercury, colored alcohol, or colored alcohol, or colored mineral spiritscolored mineral spirits

When heated, Liquid When heated, Liquid ExpandsExpands

To calibrate thermometers To calibrate thermometers and to set a standard for and to set a standard for temperature we have temperature we have chosen water to be our chosen water to be our bench mark.- Not just any bench mark.- Not just any water – water – Pure Water at Pure Water at 1ATM of Pressure1ATM of Pressure

Calibrating ThermometersCalibrating Thermometers

What About What About Fahrenheit?Fahrenheit?

We must convert with the We must convert with the following formulas:following formulas:– To find To find °F°F °°F = (9/5(F = (9/5(°C))°C)) + + 3232

– To Find To Find °°CC °C = 5/9(°F - 32)°C = 5/9(°F - 32)

With With °F and °C, often times you °F and °C, often times you get negative numbers; This is get negative numbers; This is because many things are colder because many things are colder than our standard “ice”than our standard “ice”

To eliminate neg. values for To eliminate neg. values for temperature, the Kelvin Scale was temperature, the Kelvin Scale was usedused– 0 Kelvin is as cold as anything 0 Kelvin is as cold as anything

can getcan get– From 0 K, you can only go upFrom 0 K, you can only go up

Kelvin ScaleKelvin Scale

Kelvin ScaleKelvin ScaleThe best thermal lab on The best thermal lab on

record has reached record has reached 0.0000001 K0.0000001 K

At 0K, the theory states At 0K, the theory states that atoms would cease to that atoms would cease to vibrate, liquids would vibrate, liquids would contract no more.contract no more.

Kelvin ConversionsKelvin Conversions

To find K To find K Kelvin temp = °C + 273.15Kelvin temp = °C + 273.15

To find °C To find °C °C = Kelvin Temp - °C = Kelvin Temp - 273.15273.15

Practice Problems 10A 1-5 Practice Problems 10A 1-5 pg 363pg 363

HOMEWORK 2, 4, 5, 7, 9, 10 HOMEWORK 2, 4, 5, 7, 9, 10 pg.387pg.387

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A piece of iron has a temperature of 100C. A second identical piece of iron in twice as hot. What is the temperature of the second piece of iron?

10+273=283K

283x2 = 566K

566 – 273 =

293oC

Section 10-2 Section 10-2 Defining HeatDefining Heat

Read Read andand

UnderstandUnderstandp. 365-367p. 365-367

Defining HeatDefining HeatHeat:Heat:

– Flow of energyFlow of energy– Moves in one direction, from Moves in one direction, from

hot to coldhot to cold– Symbol QSymbol Q– Has units for energy (Joule) Has units for energy (Joule)

(calorie, kilocalorie, dietary (calorie, kilocalorie, dietary calorie, Btu, therm)calorie, Btu, therm)

Mechanical Energy is Equal to Heat Energy

KE=PE=work=Q=heat

Doing work on a substance will cause it to heat up.

Specific Heat CapacitySpecific Heat Capacity

This is the amount of energy required This is the amount of energy required to change the temperature of 1kg of to change the temperature of 1kg of a substance by 1 a substance by 1 °C°C

CCpp = Q/ m = Q/ mΔT ΔT

Q = m CQ = m CPP ΔT ΔT

Q = Heat (Joules)Q = Heat (Joules)

m = mass (Kg)m = mass (Kg)

CCpp = Specific Heat (J/Kg = Specific Heat (J/Kg°C)°C)

ΔT = change in temp (ΔT = change in temp (°C)°C)

Table 10.4 Table 10.4 pg 372pg 372

Substances take Substances take differing amounts of differing amounts of energy to heat upenergy to heat up–Water heats up SlowlyWater heats up Slowly–Lead heats up fastLead heats up fast

CalorimetryCalorimetryTo determine specific heat To determine specific heat

capacity we do calorimetrycapacity we do calorimetryFor calorimetry always For calorimetry always

remember: remember: Energy absorbed = Energy releasedEnergy absorbed = Energy released

QQwaterwater = Q = Qxx

CCPwPw M Mww ΔTΔTww = C = Cpxpx M Mxx ΔT ΔTxx

Practice Probs.

Practice Probs.

p.378 1 & 2

p.378 1 & 2

10c 10c Pg.374Pg.374

7, 6, 5, 47, 6, 5, 4

Homework:

Homework:

Pg.387-388

Pg.387-388

13, 14, 16, 21, 22, 28

13, 14, 16, 21, 22, 28

p.375-376p.375-376

Q T graphsHeat Temperature Graphs

Heat FlowHeat FlowThermal ConductionThermal Conduction: this is how : this is how

heat flows through a substance. heat flows through a substance. Some materials conduct heat Some materials conduct heat well. others are very poor well. others are very poor (insulators)(insulators)

Generally, metals are good Generally, metals are good conductors of heat. Asbestos, conductors of heat. Asbestos, cork, ceramic, cardboard,& cork, ceramic, cardboard,& fiberglass are good insulatorsfiberglass are good insulators

Heat Moves in 3 WaysHeat Moves in 3 WaysConductionConduction: heat moving : heat moving

through 2 objects that touch through 2 objects that touch each othereach other

ConvectionConvection: heating by : heating by movement of fluids(liquids and movement of fluids(liquids and gases). Involves displacement gases). Involves displacement of cold matter by hotof cold matter by hot

Heat Movement Cont…Heat Movement Cont…

RadiationRadiation: electromagnetic : electromagnetic rays carry heat from rays carry heat from everything above 0 Kelvin in everything above 0 Kelvin in the form of waves. No the form of waves. No medium is needed for this- medium is needed for this- occurs in the vacuum of occurs in the vacuum of space. Also, near a campfirespace. Also, near a campfire

ThermosThermosKeeps hot things hot, Keeps hot things hot, cold things cold because cold things cold because it minimizes heat flowit minimizes heat flow

OVERHEADOVERHEAD

– Eskimo- ParkaEskimo- Parka– Arabian - Desert DressArabian - Desert Dress

Clothes & climateClothes & climate

Laws of Thermodynamics

Heat, Work, and Internal Energy Q is heat, W is Work, U is internal Energy System- A collection of matter within a clearly

defined boundary across which no matter passes.

Environment- Everything outside a system that can affect or be affected by the system’s behavior.

Defining Work in terms of Changing Volume

W = Fd Work = force x distance movedp.404 insert formula proof

Work = pressure x volume change

Pressure

p. 405 11A 1 and 2

1. A) 6.4x105 J B) -4.8x105 J

2. -167.5 J; Work is done on the gas because the volume change is negative

First Law of Thermodynamics

This law is a statement of the Law of Conservation of Energy.

Heat, Work, and the Change in Internal Energy can be calculated.

U = Q – W U-change in internal Energy Q-energy transferred to or from a system as heat W-Energy transferred to or from a system as work

Page 409

Look at the roller coaster and the bar graphs below to see an example of this view of the Conservation of Energy.

Page 413 11B problems 1-3

33J -143 J; removed as heat 10,000J

Second Law of Thermodynamics

The Universe and all systems are moving towards greater disorder.

The Entropy of the Universe increases in all natural processes.

Heat and entropy are related. Entropy increases because energy is

transferred as heat to a system.

Entropy

Entropy is a measure of a system’s disorder. Increasing disorder reduces the energy

available for work. Greater disorder means there is less energy to

do work.

Direction of Energy

Always towards a state of disorganization In order to organize energy, more energy must

be input. Clean room Salt pepper shaker Heat death of the Universe.

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Q