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Chapter 21 Thermal Energy


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Title: Chapter 21 Thermal Energy

Chapter 21 Thermal Energy
Section 1 Temperature and Thermal Energy
  • Temperature is.
  • How much heat something has or does not have.
  • Measure of the average amount of kinetic energy
    in the molecules of a substance
  • Kinetic energy movement heat
  • The higher the temp. the faster the molecules

Thermal Energy
  • The sum of the kinetic and potential energy in
  • Kinetic energy of motion
  • Potential energy stored in bonds
  • Increases when
  • Number of bonds or molecules increase
  • Motion of molecules increase
  • Space decreases

Thermal Expansion
  • Almost all substance will expand when heated and
    contract when cooled.
  • Why?
  • Gases expand more than liquids and liquids expand
    more than solids.
  • Marshmallow in microwave

Temperature scales
  • Celsius
  • Fahrenheit
  • Kelvin

H2O freezes H2O boils
0 100
32 212
273 373
  • Fahrenheit to Celsius
  • ( F 32) 5/9
  • Celsius to Fahrenheit
  • ( C 9/5) 32
  • Celsius to Kelvin
  • K C 273

Homework convert!
  • Fahrenheit to Celsius
  • 32?
  • 212?
  • 80?
  • 55?
  • 72?
  • Celsius to Fahrenheit
  • 0?
  • 100?
  • 14?
  • 27?
  • 33?
  • Convert to Kelvin
  • 0?c
  • 100?c
  • 44?c
  • 72?F
  • 11?F

(No Transcript)
Complete the flow chart.
  • Convert 31 F to Kelvin
  • Convert 250 K to Celsius.
  • Convert 320 K to Fahrenheit.

Section 2 Heat
  • Kinetic energy that is transferred from the
    molecules of one object to another.

3 ways heat is transferred
  • Conduction
  • Heat transfer by direct contact
  • Kinetic energy of molecules transfers from moving
    particles to slower moving particles
  • Hot chocolate on your tongue
  • Ice cube in your hand
  • Egg in a skillet.

  • Radiation
  • Heat is transferred electromagnetic waves
  • Waves carry energy
  • How the sun heats the earth.
  • Heat you feel from a camp fire.
  • How food is heated in a microWAVE.

  • Convection
  • Heat is transferred by molecules moving from one
    area to another in a gas or liquid
  • When boiling water for Mac and Cheese.
  • Turn stove on and burner transfers heat to pot
    through conduction.
  • Heat transfers from pot to first water molecules
    through conduction.
  • Water molecules on the bottom that have heat move
    to the top and the entire pot of water is heated
    by convection.
  • Macaroni is heated through conduction.

Natural Convection
  • Swimming pools and lakes.
  • Warmer water is always on top.
  • Wind
  • Created by cool dense air pushing its way toward
    warmer less dense air.
  • Why the ocean is a great place to fly a kite.

Thermal conductors
  • Any material that easily transfers heat.
  • Can you name a few?
  • Metals
  • Gold
  • Copper
  • Iron
  • Titanium

Thermal insulators
  • A material that heat does not flow easily.
  • Used to handle hot objects or insulate houses and
  • Wood
  • Fiberglass
  • Plastic
  • Rubber
  • Air

Thermal Absorption
  • Different materials absorb heat at different
  • On a hot summer day would you rather stand
    barefoot for an hour on a paved parking lot
    surface or on the grass?
  • Parking lot absorbs and retains heat.

Thermal pollution
  • The increase in the overall temperature of a body
    of water due to warm water inflow.
  • Plants and factories that sit on the banks of a
    river use the water to cool their machines and
    then release the warmed water back into the
    natural environment.
  • Effects
  • warm water can retain less oxygen than cool
    water. Aquatic life needs oxygen.

Assignment. 10 pts.
  • Find an article on thermal pollution caused by
    human activity.
  • Write a short paragraph explaining the impacts on
    the environment and how we as humans could fix
    the problem.
  • Design an energy efficient house. Label all
    areas where radiation, conduction, and convection
    will take place. Make sure to put a () beside
    those areas that are good for energy use and a
    (-) beside areas where the heat transfer is bad.