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HEAT ENERGY

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HEAT ENERGY What is HEAT? Form of energy and measured in JOULES Particles move about more and take up more room if heated this is why things expand if heated – PowerPoint PPT presentation

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Title: HEAT ENERGY


1
HEAT ENERGY
  • What is HEAT?
  • Form of energy and measured in JOULES
  • Particles move about more and take up more
    room if heated this is why things expand if
    heated
  • It is also why substances change from
    solids liquids gases when
    heated

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2
Heat and Temperature
  • The temperature of an object tells us how HOT it
    is
  • Measured in degrees Celsius - C
  • It is NOT the same as heat energy although the
    two quantities are related.

3
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

4
Heating and Cooling cont
  • Heat energy always moves from HOT object
    COOLER object
  • e.g.Cup of water at 20 C in a room at 30C -
    gains heat energy and heats up its temperature
    rises
  • Cup of water at 20 C in a room at 10C loses
    heat energy and cools down its temperature will
    fall.

5
HEAT ENERGY
  • Energy transfer Conduction
    Convection Radiation

6
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

7
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-particles very close
    together
  • Conduction does not occur very quickly in liquids
    or gases

8
Conductors
  • Materials that conduct heat quickly are called
    conductors
  • All metals are good conductors of heat
  • Copper is a very good conductor of heat
  • Pans for cooking are usually made with a copper
    or aluminium bottom and plastic handles

9
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 fridge has insulation material round it to keep
    it cold reduces amount of heat conducted to
    inside from the warmer room

10
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 Convection currents
  • Occur because an area with warm particles expands
    and becomes less dense than the cooler areas
    nearby. The warm area rises.Cooler particles
    fall into the space left by the warm particles
    and convection current is set up

11
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
12
Convection cont
  • The Sun can cause large convection currents -
    WINDS
  • During daytime the land warms up more than the
    sea. The warm air rises over the land and cool
    air falls over the sea. So we feel a sea breeze.
    (You will talk more about this in 8th grade)
  • Rising convection currents can be uses by glider
    pilots to keep their planes in the air and by
    birds to stay aloft.

13
Radiation
  • Transfer of heat directly form the source to the
    object by a wave, travelling as rays.
  • Heat radiation is also known as
  • All objects that are hotter than their
    surroundings give out heat as infra-red radiation
  • Heat transfer by radiation does not need
    particles to occur and is the only way energy can
    be transferred across empty space

INFRA-RED RADIATION
14
KEY WORDS
  • 1-1 Heat A form of energy
  • Heat
  • Molecule
  • Heat transfer
  • Conduction
  • Insulator
  • conductor
  • Convection
  • radiation
  • 1-2 Temperature and Heat
  • Kinetic energy
  • Temperature
  • Thermometer
  • Celsius scale
  • Kelvin scale
  • Absolute zero
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