Chapter 10: Heat Energy

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Chapter 10 Heat Energy
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Aim How is energy related to motion?
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Movement of Molecules

• The speed of molecules in an object can be sensed
  as temperature-hot, cold, warm, cool
• Faster the speed, warmer the object
• Solids
• molecules vibrate back and forth
• Lined up right on top of each other
• Liquids
• Molecules spread out more
• Vibrate and collide into one another

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• Gases
• molecules are spread out far apart
• Move in straight lines between collision
• Any object has energy due to its motion, whether
  its a molecule or car
• Energy is an ability to move other matter around

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Aim What are the two main types of energy?
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Kinetic Energy

• Energy of any moving object
• Measured in joules
• 3 forms
• Heat-sun
• Mechanical-machines
• Sound-vibrations

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Potential Energy

• Energy stored in an object or material
• Ex moving an object up hill
• 3 forms
• Atomic-radioactive materials
• Chemical- batteries
• Gravitational-any 2 masses in the universe

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Aim What is the difference between temperature
and heat?
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Temperature

• The average speed of molecules in a material
  determines the molecules average kinetic energy
• The average kinetic energy determines the
  temperature
• How hot or cold a material is
• Thermometers measure temperature

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Heat

• When energy flows between 2 objects because they
  have different temperatures
• Form of energy
• Measured in joules or calories
• Energy of a hot object flows as heat to the
  cooler object. This happens until both are the
  same temperature

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Aim What is the difference between radiation,
conduction and convection?
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Radiation

• The transfer of energy by electromagnetic waves
• Ex sun producing light
• Comes in the form of infrared, visible and
  ultraviolet rays
• Strength of each type of radiation depends on the
  temperature of the object
• Objects that absorb electromagnetic waves
  receives energy
• Effects materials temperature rises, change of
  state of material, material has a chemical change

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Conduction

• Movement of energy through direct contact
• Only way heat can travel through solids
• Heat transfer-molecules move
• Burner pan sauce

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Convection

• Heat transfer
• Occurs in liquids and gases
• Transfer of energy by the flow of a liquid or gas
• Warm air carries heat up

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Aim What is insulation?
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Insulation

• Prevents heat from flowing in or out of a
  material
• Use a material that is not a good conductor of
  heat
• Examples
• Insulation in a house-contains fiberglass and a
  lot of air
• Foam used to keep foods cold

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Aim What causes thermal expansion?
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Thermal Expansion

• Any kind of matter expanding when its
  temperature is raised
• Examples
• Bimetallic strip-one metal expands more than the
  other causing the thermostat to turnoff
• Steel is placed in roadways to prevent them from
  bending on the hottest days

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• As the temperature of a solid, liquid or gas is
  raised, the particles move around faster and take
  up more space
• This causes the material to increase in volume
• Different materials expand or contract at their
  own rate
• Hot glass can shatter easily when placed in cold
  water because of unequal contraction

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Aim What is pressure?
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Pressure

• Is the force on each unit of area of a surface
• is the result of colliding gas molecules that
  push on each unit of a surface
• 2 laws explain pressure

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Boyles Law

• Air enters the pump when you pull up the
  handle-particles are spread out
• When you press down on the handle the particles
  are forced into a smaller volume
• Smaller volume, higher pressure
• Larger volume, lower pressure
• Higher pressure forces air into the tire

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Charles Law

• Change in temperature affects pressure
• Volume of a gas increases when we raise its
  temperature while keeping its pressure constant
• Volume of gas decreases when the temperature
  decreases, pressure is constant

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Aim What causes changes of state?
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Changes of State

• States solid, liquid or gas
• Removing or adding energy causes matter to change
  from one state to another
• Melting solid to liquid
• Particles move faster as the temperature is
  raised
• Vaporization liquid to gas
• If heat is applied particles will continue to
  move faster and faster

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• Condensation gas to liquid
• Heat is removed from a gas
• Particles slow down as the temperature falls
• Freezing liquid to solid
• Energy is removed steadily
• Particles become locked into fixed positions
• Temperature of a substance does not change while
  a change of state occurs
• Temperature changes only when all of the
  substance has changed state

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• boiling-temperature stays unchanged while a
  liquid is boiling
• Occurs when bubbles of vapor escape from a liquid
• Evaporation-particles vaporize at the surface
  when turning a liquid into a gas

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Aim How is a forced-air heating system different
from a steam-heating system?
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Steam Heat

• Changes of state in water are used to transfer
  energy from the furnace to air in the room
• Furnace heats the water causing vaporization
• Steam is produced and sent through the radiator
• Air in the room is heated by conduction-air comes
  into contact with hot radiator

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• Radiation-waves of energy (infrared) are spread
  through the room
• Air circulates through the room by convection
• hot air rises and cooler air sinks down

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Forced-Air Heat

• Does not involve changes of state
• Buildings are heated with air alone
• Hot air is forced up from the furnace and blown
  out through vents
• Convection helps circulate air
• Cooler air exits through air duct and enters air
  blower to be heated by the furnace

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Aim How do gases drive a car?
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Aim How can the suns energy be used?
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Solar Heating

• 2 types of solar heating
• Active solar heating
• Sun heats water
• Pump circulates the heat throughout the building
• Passive solar heating
• Thick wall stores heat from the sun
• Heat is distributed by convection

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Solar Cells

• Scientists developed materials made of silicon
  that produce electrons called solar cells
• Solar cells generate an electric current from
  sunlight
• Can power vehicles
• Can provide electricity to buildings

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Aim How are fossil fuels formed?
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Fossil Fuels

• The remains of plants and animals are buried
  under sand or mud
• Over time, pressure turns them into a thick oil
  or gas
• Ex coal, oil, natural gas
• Give off large amounts of heat when burned
• Are nonrenewable resources

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Aim How can modern plant and animal matter give
us energy?
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Biomass conversion

• Animal and plant matter is changed into high
  quality fuels
• Enables us to conserve fossil fuels
• Fuels produced are examples of renewable
  resources
• 2 methods
• Yeast cells used
• Grain is mixed with yeast cells
• Change sugar in grains to ethyl alcohol and CO2
• Ethyl alcohol is a good fuel and can be mixed
  with gasoline

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• 2. Bacteria used
• Bacteria is used to digest wastes where air is
  lacking
• Garbage from landfills is placed in airtight
  tanks
• Bacteria produce methane gas-main ingredient of
  natural gas

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Aim What are the advantages and disadvantages of
nuclear fusion and fission?
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Aim Which is better fission or fusion?
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Aim What are other sources of energy?
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Wind Energy

• For centuries farmers have been using windmills
  to pump water on farms
• Many small wind driven electric generators were
  built between 1930 and 1960
• The production of windmills stopped when electric
  companies strung wires in most parts of the
  country
• Now there is a growing demand for energy

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• Manufacturers have started to build wind turbines
  to convert wind into electricity
• Most of them are located in California
• 1 of Californias energy comes from these
  turbines
• This source of energy is clean and renewable

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Hydroelectricity

• Flow of water causes turbines to spin to drive a
  generator producing electricity
• US gets 15 of its electricity from this source
• Hoover Dam
• Causes little pollution
• Few of sites where dams can be built
• Need to carefully plan the building of a dam-do
  not want to harm plant and animal species