THERMAL (HEAT) ENERGY

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THERMAL (HEAT) ENERGY

• What is HEAT?
• Particles move around more and take up more
  room if heated this is why things expand when
  theyre hot
• It is also why substances change from
  solids liquids gases when
  heated

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Heat and Temperature

• The temperature of an object tells us how HOT it
  is
• Measured in degrees Celsius - C

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Heating and Cooling

• If an object has become hotter, it means that it
  has gained heat energy.
• If an object cools down, it means it has lost
  energy

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Heating and Cooling cont

• Thermal energy always moves from HOT object
  COOLER object

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HEAT ENERGY

• 3 Types of Thermal Energy Transfer
• ConductionConvection
• Radiation

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Conduction

• Heat is transferred through a material by being
  passed from one particle to the next
• Particles at the warm end move faster and this
  then causes the next particles to move faster and
  so on.
• In this way heat in an object travels fromthe
  HOT end the cold end

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Conduction cont

• Occurs by the particles hitting each other and so
  energy is transferred.
• Can happen in solids, liquids and gases,
• Happens best in solids, where particles very
  close together
• Conduction does not occur very quickly in liquids
  or gases

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Conductors

• Materials that conduct heat quickly are called
  conductors
• All metals are good conductors of heat
• Copper and aluminium are very good conductor of
  heat
• Pans for cooking are usually made with a copper
  or aluminium bottom and plastic handles

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Insulators/Poor Conductors

• Materials that conduct heat slowly or poorly are
  called insulators
• Glass, wood, plastic and rubber are poor
  conductors (good insulators)
• Nearly all liquids including water are poor
  conductors (good insulators)
• Gases, including air are poor conductors,e.g.,
  wool feels warm because it traps a lot of air
• A refrigerator has insulation material around it
  to keep it cold it reduces amount of heat
  conducted to inside from the warmer room

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Convection

• Takes place in material where particles can move
  around inside the material, i.e. liquid or gas
• The heat is carried by the particles themselves
  moving
• Occurs because an area with warm particles
  expands and becomes less dense than the cooler
  areas nearby. The warm particles rise.Cooler
  particles fall into the space left by the warm
  particles. This process is called a convection
  current.

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Convection Currents

• Hot liquids and gases expand and rise while the
  cooler liquid or gas falls

2. Goes across
3. Then down
1. Hot air rises
4. And across
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Convection cont

• The sun can cause large convection currents -
  WINDS
• During daytime the land warms up more than the
  ocean. The warm air rises over the land and cool
  air falls over the ocean, so we feel a sea
  breeze.

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Radiation

• Transfer of heat directly form the source to the
  object by a wave, travelling as rays
• Thermal radiation is also known as
• All objects that are hotter than their
  surroundings give out heat as infra-red
  radiation.
• Heat transfer by radiation is the only way energy
  can be transferred across empty space.

INFRA-RED RADIATION
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Thermal Radiation
Dull dark materials aregood radiators
Bright shiny materials are poor radiators
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Absorbers
Shiny, bright canPoor absorber
Dull black canGood absorber
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Key Words
Temperature
Cold
Insulator
Radiation
Heat
Transfer
Convection
Conduction
Conductor