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Temperature and Heat

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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. - PowerPoint PPT Presentation
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Temperature and Heat Heat Temperature Internal Energy Measurement of Heat Specific Heat Thermal Expansion
Transcript
Page 1: Temperature and Heat

Temperature and Heat

Heat

Temperature

Internal Energy

Measurement of Heat

Specific Heat

Thermal Expansion

Page 2: Temperature and Heat

Temperature & Heat

• Absolute Zero Video – Nova

• Heat Mixes Lab

• Antifreeze in the Summer Lab

Page 3: Temperature and Heat

Temperature

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

Page 4: Temperature and Heat

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.

Page 5: Temperature and Heat

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.

Page 6: Temperature and Heat

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.

Page 7: Temperature and Heat

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.

Page 8: Temperature and Heat

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.

Page 9: Temperature and Heat

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.

Page 10: Temperature and Heat

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

Page 11: Temperature and Heat

Thermal Equilibrium

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

Page 12: Temperature and Heat

How do we measure temperature?

Think about using a thermometer

Page 13: Temperature and Heat

How does the thermometer know how hot the substance is?

Page 14: Temperature and Heat

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.

Page 15: Temperature and Heat

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

Page 16: Temperature and Heat

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

Page 17: Temperature and Heat

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.

Page 18: Temperature and Heat

Specific Heat Table

Page 19: Temperature and Heat

Thermal Expansion

• Why?

• The Bridge Connection Lab

• Concept Development - Thermal Expansion

Page 20: Temperature and Heat

Thermal Expansion

Page 21: Temperature and Heat

Thermal Expansion

Page 22: Temperature and Heat

Thermal Expansion

• Bimetallic Strip

• Ball and ring

• Drinking Bird

• Soda Can (Yes, I can make it work!)

Page 23: Temperature and Heat

Expansion of Water

• This is a good thing.

• Water temp. vs. depth.

Page 24: Temperature and Heat

Yeah! Chapter Problems.

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

Page 25: Temperature and Heat

Heat Transfer

• Conduction

• Convection

• Radiation

• Absorption of Radiant Energy

• Emission of Radiant Energy

• Newton’s Law of Cooling

• Global Warming / Greenhouse Effect

Page 26: Temperature and Heat

Solar Equality Lab

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

Page 27: Temperature and Heat

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

Page 28: Temperature and Heat

Conduction

• Conduction –

• Conductor –

• Insulator

Page 29: Temperature and Heat

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…)

Page 30: Temperature and Heat

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

Page 31: Temperature and Heat

Convection

• Convection -

Page 32: Temperature and Heat

Convection

• Energy transfer through the bulk motion of hot material

• Examples– Space heater– Gas furnace (forced)

• Natural convection mechanism - “hot air rises”

Page 33: Temperature and Heat

Heat TransferConvection in a House

Page 34: Temperature and Heat

Heat TransferThe Wind

Sea Breeze Land Breeze

Page 35: Temperature and Heat

Convection

• Why does rising warm air cool?

Page 36: Temperature and Heat

Heat TransferConvection on the Sun

Page 37: Temperature and Heat

Heat TransferThermos Bottle

Page 38: Temperature and Heat

Radiation

• Radiation

Page 39: Temperature and Heat

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

Page 40: Temperature and Heat

Radiation

• Absorption of Radiant Energy –

• Emission of Radiant Energy –

• Con. Dev. 22-1 Transmission of Heat

Page 41: Temperature and Heat

Solar Energy Lab 56

Page 42: Temperature and Heat

Newton’s Law of Cooling

Page 43: Temperature and Heat

Global Warming

• What causes it?

Page 44: Temperature and Heat

Greenhouse Effect

Page 45: Temperature and Heat

Video

• An Inconvenient Truth

Page 46: Temperature and Heat

Yeah! More Problems

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

Page 47: Temperature and Heat

Chapter 24

Thermodynamics:

Laws of Thermodynamics Song:

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

Page 48: Temperature and Heat

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

Page 49: Temperature and Heat

Absolute Zero

• Define:

• Compared to Celsius:

Page 50: Temperature and Heat

Lab

• The Uncommon Cold - #63

Page 51: Temperature and Heat

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

Page 52: Temperature and Heat

1st Law of Thermodynamics

• Define

• Heat added =

Page 53: Temperature and Heat

The first law of thermodynamics

• Conservation of energy

• Components– Internal energy– Heat – Work

• Stated in terms of changes in internal energy

• Application: heat

engines

Page 54: Temperature and Heat

Adiabatic Process

• Define:

Page 55: Temperature and Heat

Adiabatic Process

• Piston in engines:

Page 56: Temperature and Heat

2nd Law of Thermodynamics

• Define:

Page 57: Temperature and Heat

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)

Page 58: Temperature and Heat

Heat Engines

Definition:

Page 59: Temperature and Heat

Heat Engines

Page 60: Temperature and Heat

Carnot (ideal) Efficiency

• Ideal Efficiency =

• Example:

Page 61: Temperature and Heat

Order Tends to Disorder

• Entropy:

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

Page 62: Temperature and Heat

Entropy

• Things:

• Living systems:

• Useful energy:

Page 63: Temperature and Heat

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.

Page 64: Temperature and Heat

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!

Page 65: Temperature and Heat

Kinetic Theory & Gas LawsPressure & Number of Molecules

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

• p N

Page 66: Temperature and Heat

Kinetic Theory & Gas Laws Pressure & Temperature

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

• p T

Page 67: Temperature and Heat

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/

Page 68: Temperature and Heat

Since we Mentioned Steam Engines

Thomas and his prototype

Page 69: Temperature and Heat

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

Page 70: Temperature and Heat

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.

Page 71: Temperature and Heat

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.

Page 72: Temperature and Heat

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

Page 73: Temperature and 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

Page 74: Temperature and Heat

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

Page 75: Temperature and Heat

Phases of MatterSolid

• Molecules arranged in a rigid crystalline structure.

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

Page 76: Temperature and Heat

Phases of MatterLiquids

• Molecules not in a lattice.

• Molecules can vibrate and rotate.

• Molecules are still close together.

• Take the shape of container.

Page 77: Temperature and Heat

Phases of MatterGas

• Molecules relatively far apart.

• Molecules have high speed of Kinetic Energy.

Page 78: Temperature and Heat

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.

Page 79: Temperature and Heat

Latent Heat

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

Page 80: Temperature and Heat

Latent Heat Graph


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