energy transfers

• energy can be transferred usefully, stored or dissipated but cannot be created or destroyed

  • in all system changes - energy is dissipated, stored in less useful ways, described as being 'wasted'
• reducing energy waste


  lubrication:

  • oil in a motor
  • reduces friction
  • less energy is lost (as heat) through friction

  thermal insulation:

  • double glazing
  • less useful thermal energy is lost
• thermal conductivity


  the higher the thermal conductivity of a material (heat is allowed to travel through material more easily), the higher the rate of energy transfers

  
  

  thermal conductivity in a building:

  • rate of cooling is low if walls are thick and thermal conductivity of walls are low
  • if walls are thin metal sheets, heat would be lost very quickly
• efficiency



  ratio of useful work done to the energy supplied to it, often expressed as %

  -efficiency = useful energy or power output / total energy or power input

  efficiency of a system can be increased by:

  • reducing waste output (lubrication, thermal insulation etc.)
  • recycling waste output (e.g. absorbing thermal waste and recycling as input energy)