Chapter 14: Thermal Energy & Heat

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Chapter 14 Thermal Energy Heat
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Introduction

• Heat is the transfer of thermal energy.

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Topics of Discussion

• Temperature and Thermal Energy (Section1)
• The Nature of Heat (Section 2)
• Thermal Energy and States of Matter (section 3)
• Uses of Heat (Section 4)

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TEMPERATURE and THERMAL ENERGY(Section one)

• Temperature is the measure of the average kinetic
  energy of the individual particles in an object.
• Three common Temperature scales for measuring
  temperature
• Fahrenheit
• Celcius
• Kelvin

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Fahrenheit

• U.S. System
• Water Freezes at 32o
• Water Boils at 212o
• 180 equal intervals between freezing and boiling
  called degrees Fahrenheit (oF)
• Absolute zero is -460o

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Absolute Zero

• Absolute zero is the lowest temperature possible.
• At this temperature, no more energy can be
  removed from matter.
• -460oF
• -273oC
• 0 K

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Celcius Scale

• This system is used in most of the world.
• Water Freezes at 0o
• Water Boils at 100o
• 100 equal intervals between freezing and boiling
  called degrees Celcius (oC)
• Absolute zero is -273o

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Kelvin Scale

• This system is used most in physical science.
• The Kelvin scale is defined so that zero is
  absolute zero.
• Units on the Kelvin scale are the same size as
  those in Celcius called kelvins (K)
• Water Freezes at 273o
• Water Boils at 373o
• Absolute zero is 0o

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Thermal Energy

• Temperature is a measure of the average kinetic
  energy of the individual particles of matter.
• Thermal energy is the total energy of all of the
  particles.

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The Nature of Heat(Section 2)

• Heat is thermal energy moving from a warmer
  object to a cooler object. (Only One way.)
• Heat is transferred by
• Conduction,
• Convection, and
• Radiation.

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Conduction

• Heat is transferred from one particle of matter
  to another without the movement of matter itself.
• Ex A pot heating on a stove. The fast moving
  (hot) particles of the element collide with the
  slow (cold) particles of the pot and energy is
  transferred.

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Convection

• Heat is transferred by the movement of currents
  within a fluid (liquid or gas.)
• Ex Water heating in a pot on the stove.
• Differing densities cause the water to flow in a
  convection current.

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Radiation

• The transfer of energy by electromagnetic
  radiation.
• Radiation does not require matter to transfer
  thermal energy.
• Ex Heat from the sun, heat lamp, and a microwave
  oven.

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Conductors and Insulators

• Conductor A material that conducts (transfers)
  heat well.
• Ex metal.
• Insulator A material that does not conduct heat
  well.
• Ex Wood, Glass and gasses.

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Specific Heat

• Specific Heat The amount of energy required to
  raise the temperature of one kilogram of a
  substance by 1 kelvin.
• ? energy Mass X Specific heat X ?
  temperature(? change)

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Thermal Energy andStates of Matter(Section 3)

• Three States of matter
• Solids
• Liquids
• Gases

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Solids

• Ex Ice cube text book
• Tightly packed particles
• Particles in fixed position (vibrate)
• Definite volume shape

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Liquids

• Ex Water Molten steel
• Particles close together (further than solid)
• Particles can move around
• Definite volume, random shape

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Gases

• Ex Steam air
• Fast moving / far apart particles
• Particles free to move
• Random volume, random shape(Expand to fit space
  available)

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Changes of State

• Change of state is the physical change from one
  state to another.
• Matter will change from one state to another if
  thermal energy is absorbed or released.
• Solid-Liquid
• Liquid-Gas
• Temperature constant

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Solid LiquidChanges of State

• Melting
• From solid to liquid
• Thermal energy increases
• Melting point temperature at which a solid
  changes to liquid
• Freezing
• From liquid to solid
• Thermal energy decreases
• Freezing point temperature at which a liquid
  changes to solid

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Liquid - GasChanges of State

• Vaporization
• From liquid to gas
• Thermal energy increases
• Boiling point temperature at which a liquid
  changes to gas
• Condensation
• From gas to liquid
• Thermal energy decreases

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Thermal Expansion

• As thermal energy of a substance increases, its
  particles spread out and the substance expands.
• Thermometers
• Expanding liquid Mercury or alcohol
• Thermostats
• Expanding bimetallic strips

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Uses of Heat(Section 4)

• Heat Engines
• convert thermal energy to mechanical energy
• External Combustion Engines
• Fuel is burned outside the engine
• Internal Combustion Engines
• Fuel is burned in cylinders inside the engine.

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Internal Combustion Engines

• Gasoline and Diesel
• Pistons move up and down (one stroke) to drive
  crankshaft
• Two Stroke
• Four- Stoke
• Intake Stroke, Compression Stroke
• Intake Stroke, Compression Stroke
• Ignition
• Power Stroke, and Exhaust Stroke

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Refrigerators

• A refrigerator is a device that uses an outside
  energy source to transfer thermal energy from a
  cool area to a warm area.

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Key Terms