Heat Transfer

Heat Transfer

Heat
1. A form of energy
  1. Always flows from a hot object to a cool object
2. measured in Joules (j)
3. Another name is thermal energy
Temperature
1. Describes how hot or cold an object is
2. Measured in Degree Celsius
The amount of energy stored in something depends on
1. The temperature
2. Material
3. Mass
Heat conductor
1. When heat travels through it is called conduction
2. Can be called thermal conductor
3. Metal is a good conductor
Heat insulator
1. Poor heat conductor
2. Wood and plastic are good insulators
3. Carpets are good insulators
  1. They contain trapped air
    1. Air is a good insulator if it cannot move
Heat energy transfer through solids
1. When a solid is heated the particles gain energy and vibrate more
  1. The particles bump into each other and pass the energy on
    1. Conduction happens best in a solid because the particles are close together
      1. Particles need more space so the solid expands
        When it cools down the particles move more slowly and the solid contracts
        When a solid expands the mass stays the same but it takes up more space and its density decreases
Heat energy travelling through liquids
1. Liquids and gases are all fluids
2. Conduction doesn't work well with fluids but convection does
  1. When a fluid is heated the particles move faster
    1. The fluid expands and becomes less dense
      1. This is because the same mass of the fluid is taking up more space
        If only parts s of the fluid is being heated that part starts to rise because it is less dense than the cooler fluid around it
        Cooler fluid moves to take its place and a convection current is formed
        Convection current plays a large part in the weather
        Convection current can also form when parts of a fluid is colder than its surrounding
Evapourating cools things down
1. 3 states of matters
  1. Solid, liquids and gases
    1. Heat a solid (e.g. water) and it will melt into a liquid when the temperature reaches its melting point.
      1. Freezing and melting points are always the same temperature.
    2. Liquid water will evaporate to form a gas
      1. The boiling point of a liquid is the same temperature when the liquid is evaporating as fast as it can
      2. When a liquid, starts to turn into a solid the temperature reaches its freezing point
    3. Gas can be changed into liquid by cooling it down until the gas condenses into a liquid
    4. Changing for solid to liquid needs energy to break the bonds holding the particles together
      1. When a liquid turns back into a solid , this energy is no longer needed
Radiation
1. Heat given from an object
  1. When hot things emit infrared radiation and it hits an object, the object will absorb the radiation or it will reflect it
    1. Light coloured, shiny materials reflect the most infrared radiation
2. Sometimes called infrared radiation
3. Thermal energy
  1. create pictures of heat rather than light
  2. measure infrared radiation and convert the data into maps of temperatures
  3. used for filming at night and finding temperature pf remote parts of the earth by taking pictures from space

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