Temperature and Heat

Heat

Temperature

Internal Energy

Measurement of Heat

Specific Heat

Thermal Expansion

Temperature & Heat

• Absolute Zero Video – Nova

• Heat Mixes Lab

• Antifreeze in the Summer Lab

Temperature

• The quantity that tells how hot or cold something is compared with a standard.

Temperature

• Temperature is a measure of the average kinetic energy of the molecules of a substance.

• A thermometer measures this KE as the molecules collide with the thermometer’s bulb.

Temperature ScalesFreezing point to boiling point of water

• Fahrenheit: 32 to 212, range of 180 degrees.

• Celsius: 0 to 100, range of 100 degrees.

• Kelvin: 273 to 373, range of 100 degrees.

Kelvin Scale

• At constant pressure the volume of a gas changes by 1/273 of its volume at 0Co with each 1Co change in temperature.

• At -273 0Co the gas is reduced to 273/273 and the volume is 0.

Heat

Some two hundred years ago heat was thought to be aninvisible fluid called caloric, which flowed like water from hot objects to cold objects. Caloric appeared to be conserved –that is, it seemed to flow from one place to another without being created or destroyed. This idea was the forerunner of thelaw of conservation of energy.

Heat is Kinetic Energy• During the French Revolution Count Von Rumford

(Benjamin Thompson) was boring cannons for the Bavarian army and he notice:

“I perceived, by putting my hand into the water and touching the outside of the cylinder that, Heat was generated; … at 2 hours and 30 minutes it (the

water) ACTUALLY BOILED…without any fire.”

• The generation of heat was related to the kinetic energy of truing the cannon barrel.

HeatHeat is the net energy transferred from one object to

another because of a temperature difference.

Internal Energy Includes:• molecular translation

form place to place,• molecular vibration,• molecular rotate.

Heat versus temperature

Temperature• A measure of hotness or

coldness of an object• Based on average

molecular kinetic energyHeat • Based on total internal

energy of molecules• Doubling amount at

same temperature doubles heat

Thermal Equilibrium

• When object on contact with each other reach the same temperature and heat no longer flows between them.

How do we measure temperature?

Think about using a thermometer

How does the thermometer know how hot the substance is?

The molecules of the substance bump into the thermometer and transfer energy. How often and how hard they bump into the thermometer are directly related to their speed. Temperature turns out to be related to the average speed of the molecules in a substance.

Temperature is not a measure of the total amount of energy in an object.

Thermal Energy = internal energy = a measure of the total kinetic and potential energy in an object

Measurement of Heat

• Heat is energy and thus has units of Joules.

• However, heat has a special unit of calorie.

• A calorie is the heat needed to raise one gram of water by 1Co.

• 1cal = 4.186J

• 1kcal = 1000 cals

• 1Cal (food calorie) = 1000 cals

Specific Heat

• Each substance has its own specific heat.• The specific heat of any substance is the amount

of heat it takes to raise 1kg of the substance by 1Co.

• Specific heat of water = 1.000 kcal/kgCo.• H = mcWhere:

m = massc = specific heatT = change in temperature.

Specific Heat Table

Thermal Expansion

• Why?

• The Bridge Connection Lab

• Concept Development - Thermal Expansion

Thermal Expansion

Thermal Expansion

Thermal Expansion

• Bimetallic Strip

• Ball and ring

• Drinking Bird

• Soda Can (Yes, I can make it work!)

Expansion of Water

• This is a good thing.

• Water temp. vs. depth.

Yeah! Chapter Problems.

• Chapter 21: 2, 4, 5, 9, 10, 12, 13, 14, 15, 17, 19, 20, 23, 26, 28, 30, 31, 33 & 34.

Heat Transfer

• Conduction

• Convection

• Radiation

• Absorption of Radiant Energy

• Emission of Radiant Energy

• Newton’s Law of Cooling

• Global Warming / Greenhouse Effect

Solar Equality Lab

• Purpose: To determine the power output of the sun.

Heat Transfer

Three mechanisms for heat transfer due to a temperature difference

1. Conduction2. Convection3. Radiation

Natural flow is always from higher temperature regions to cooler ones

Conduction

• Conduction –

• Conductor –

• Insulator

Conduction

• Heat flowing through matter

• Mechanism– Hotter atoms collide

with cooler ones, transferring some of their energy

– Direct physical contact required; cannot occur in a vacuum

• Poor conductors = insulators (Styrofoam, wool, air…)

Sample conductivities

Material Relative conductivity

Silver 0.97

Iron 0.11

Water 1.3x10-3

Styrofoam 1.0x10-4

Air 6.0x10-5

Vacuum 0

Convection

• Convection -

Convection

• Energy transfer through the bulk motion of hot material

• Examples– Space heater– Gas furnace (forced)

• Natural convection mechanism - “hot air rises”

Heat TransferConvection in a House

Heat TransferThe Wind

Sea Breeze Land Breeze

Convection

• Why does rising warm air cool?

Heat TransferConvection on the Sun

Heat TransferThermos Bottle

Radiation

• Radiation

Radiation

• Radiant energy - energy associated with electromagnetic waves

• Can operate through a vacuum • All objects emit and absorb radiation• Temperature determines

– Emission rate– Intensity of emitted light– Type of radiation given off

• Temperature determined by balance between rates of emission and absorption– Example: Global warming

Radiation

• Absorption of Radiant Energy –

• Emission of Radiant Energy –

• Con. Dev. 22-1 Transmission of Heat

Solar Energy Lab 56

Newton’s Law of Cooling

Global Warming

• What causes it?

Greenhouse Effect

Video

• An Inconvenient Truth

Yeah! More Problems

• Chapter 22: 1, 2, 3, 4, 7, 8, 9, 12, 16, 17, 19, 20, 21, 22, 24, 25, 26, 27 & 28.

Chapter 24

Thermodynamics:

Laws of Thermodynamics Song:

http://www.youtube.com/watch?v=KTHiIwxcexI

Thermodynamics

• The study of heat and its relationship to mechanical and other forms of energy

• Thermodynamic analysis includes – System– Surroundings

(everything else)– Internal energy (the

total internal potential and kinetic energy of the object in question)

• Energy conversion– Friction - converts

mechanical energy into heat

– Heat engines - devices converting heat into mechanical energy

– Other applications: heat pumps, refrigerators, organisms, hurricanes, stars, black holes, …, virtually any system with energy inputs and outputs

Absolute Zero

• Define:

• Compared to Celsius:

Lab

• The Uncommon Cold - #63

Kinetic Theory & Gas Laws Temperature & Volume

Charles’ Law Jacques Charles (1746-1823)

• The volume of a fixed amount of gas at constant pressure is directly proportional to its absolute (Kelvin) temperature.

• V = kThttp://www.grc.nasa.gov/WWW/K-12/airplane/aglussac.html

1st Law of Thermodynamics

• Define

• Heat added =

The first law of thermodynamics

• Conservation of energy

• Components– Internal energy– Heat – Work

• Stated in terms of changes in internal energy

• Application: heat

engines

Adiabatic Process

• Define:

Adiabatic Process

• Piston in engines:

2nd Law of Thermodynamics

• Define:

The second law of thermodynamics

Equivalent statements: • No process can solely convert a quantity of

heat to work (heat engines)

• Heat never flows spontaneously from a cold object to a hot object (refrigerators)

• Natural processes tend toward a greater state of disorder (entropy)

Heat Engines

Definition:

Heat Engines

Carnot (ideal) Efficiency

• Ideal Efficiency =

• Example:

Order Tends to Disorder

• Entropy:

• http://www.youtube.com/watch?v=5KIhDVLbMeY&feature=related

Entropy

• Things:

• Living systems:

• Useful energy:

More physics fun

• Chapter 24 # 1, 3, 4, 6, 11, 12, 31, 32 & 33.

• Chapter 24 # 13, 19, 21, 22, 23, 24, 37, 39 & 40.

Second law, third statement

• Real process = irreversible process

• Measure of disorder = entropy

Second law, in these terms:

• The total entropy of the Universe continually increases

• Natural processes degrade coherent, useful energy– Available energy of

the Universe diminishing

– Eventually: “heat death” of the Universe

• Direction of natural processes– Toward more disorder– Spilled milk will never

“unspill” back into the glass!

Kinetic Theory & Gas LawsPressure & Number of Molecules

• Pressure is directly proportional to the number of gases molecules present.

• p N

Kinetic Theory & Gas Laws Pressure & Temperature

• At constant volume pressure is directly proportional to the Kelvin temperature.

• p T

Kinetic Theory & Gas Laws Pressure & Temperature

A boiler explosion broke this locomotive into small pieces and sprayed them, and the crew, over a wide area of Florida.

http://afu.com/steam/

Since we Mentioned Steam Engines

Thomas and his prototype

Kinetic Theory & Gas Laws Pressure & Volume

Boyle’s LawRobert Boyle (1627 – 1691)

• At constant temperature pressure is inversely proportional to the volume.

• p 1/V where V = volume.

http://www.grc.nasa.gov/WWW/K-12/airplane/aboyle.html

Kinetic Theory & Gas Laws Ideal Gas Law

• Putting all three of these together the Ideal Gas Law is obtained.

• P (NT)/V

• The proportionally can be used to take ratios for calculations.

• p2/p1 = (V1/V2)(T2/T1) assuming a constant number of molecules, N.

Kinetic Theory and AtomsJohn Dalton (1766 – 1844)

• All matter is composed of tiny particles.• All atoms of each element are identical (he didn’t

know about isotopes.)• Atoms are not created or destroy in chemical

reactions (conservation of matter.)• Elements bond in whole ratios to form

compounds.• Chemical reactions are the union and separation of

atoms.

Energy, heat, and molecular theory

Two responses of matter to heat

1. Temperature increase within a given phase– Heat goes mostly into

internal kinetic energy– Specific heat

2. Phase change at constant temperature– Related to changes in

internal potential energy

– Latent heat

Phase changes

Solid/liquid Liquid/gas Solid/gas

Latent heat Fusion Vaporization Sublimation

Temperature

(Direction ->)

Melting point Boiling point Sublimation

Temperature

(Direction <-)

Freezing point

Condensation point

Sublimation

Evaporation and condensation

• Individual molecules can change phase any time

• Evaporation:– Energy required to

overcome phase cohesion

– Higher energy molecules near the surface can then escape

• Condensation: – Gas molecules near the

surface lose KE to liquid molecules and merge

Phases of MatterSolid

• Molecules arranged in a rigid crystalline structure.

• Expansion occurs during heating because molecules vibrate with grater amplitude.

Phases of MatterLiquids

• Molecules not in a lattice.

• Molecules can vibrate and rotate.

• Molecules are still close together.

• Take the shape of container.

Phases of MatterGas

• Molecules relatively far apart.

• Molecules have high speed of Kinetic Energy.

Latent Heat

• Heat associated with a phase change.

• Lf = latent heat of fusion

• H = m Lf = heat needed to melt a substance.

• Lv = latent heat of vaporization

• H = m Lv = heat needed to vaporize a substance.

Latent Heat

Latent heat of fusion used to break apart the crystalline lattice of water.

Latent Heat Graph