science 10

• expansion


  an increase in the volume of a solid, a liquid or a gas when its temperature rises. This is the opposite of contraction.
• contraction


  a decrease in the volume of a solid, a liquid or a gas when its temperature falls. This is the opposite of expansion.
• Heat or thermal energy can flow by conduction, convection, or radiation
• Dark matt surfaces are better at absorbing and radiating heat energy than light shiny surfaces
• Light shiny surfaces reflect more heat energy back into space compared to dark matt surfaces which absorb most of the incoming heat energy
• A large surface area means that there will be many opportunities for heat to escape so the rate of heat loss increases with increasing surface area
• Heat is initially transferred through the glass wall of the beaker by conduction. The water in the region of the Bunsen flame is heated, and expands, becomes less dense and rises. It is replaced by the cooler, denser water which surrounds it. The water is in turn heated, expands, becomes less dense and rises, creating the convection current
• Why is the water at the top hotter?

  Hot water is less dense, so it rises to the top
• example drawing and labelling

  
• conduction


  the transfer of thermal energy without the physical movement of the medium
• heat can be transferred by:

  • conduction
  • radiation
  • convection
• convection

  the transfer of thermal energy from one place to another by the physical movement of a medium
• fluids transfer heat mainly by convection
• thermal insulators are materials that prevent or slow down the flow of heat
• solids transfer heat mainly by conduction
• gases transfer heat mainly by radiation
• convection diagram

  
• radiation


  the transfer of energy from a hotter body to a cooler body without the need for a medium
• heat energy from sun to earth in a vacuum can only be transferred by radiation
• heat energy transferred by radiation can be absorbed

  or reflected
• factors that affect the rate of conduction

  • material of an object
• factors that affect rate of radiation

  • temperature of object
  • surface area of object (allows heat to be radiated from the object more quickly)
  • type (texture or colour) of surface
• absorption of radiation


  dull and rough, and black surfaces are better absorbers of radiation than smooth and shiny, and white surfaces
• emission of radiation


  dull and rough, and black surfaces are better emitters of radiation than smooth and shiny, and white surfaces
• smooth and shiny and white surfaces

  reflect radiation
• Combustion

  Chemical reaction in which a substance is heated in the presence of oxygen to form one or more new substances. Heat and light are usually given out during combustion.
• example of combustion


  when petrol undergoes combustion inside the engine of a moving car, chemical potential energy in the petrol is converted to kinetic energy.
• In sg eg of combustion

  
  

  combustion of natural gas is the main method used to generate electricity in power plants
• thermal decomposition

  the process in which a substance breaks down into two or more simpler substances upon heating
• oxidation


  process when substance gains oxygen
• example of oxidisation


  cellular respiration, rusting