Energy

• kilogram (kg)


  Unit of mass
• joule (J)


  Unit of energy
• metre (m)


  Unit of length
• metre/second (m/s)


  Unit of speed
• second (s)


  Unit of time
• watt (W)


  Unit of power
• metre/second2 (m/s2)


  Unit of acceleration
• newton (N)


  Unit of force
• Energy Transfer


  Describes how thermal energy transfer may take place by conduction, convection and radiation
• Conduction, convection and radiation do not occur in solids
• Convection


  Upward movement of warmer fluid, replaced by cooler fluid
• Emission and absorption of radiation


  Related to surface and temperature, shiny vs matte
• Reducing unwanted energy transfer

  Insulation, clothes, houses
• Conduction


  Heated molecules passing onto others, no movement of molecules (vibration)
• Solids


  Good conductors due to close together molecules
• Convection


  Through liquids and gases (not solids), upward movement of warmer fluid, replaced by cooler fluid
• Radiation


  Gases and liquids are better radiators than solids, hotter the object the more radiation
• Absolute zero (-273°C) is the temperature at which all thermal radiation ceases
• Infrared (IR) waves


  Heats up faster than visible light
• Radiator heats up, causing air to rise and cool air to fall, creating a convection current
• Conduction doesn't involve movement, solids are best conductors (metals)
• Air is a good insulator
• Convection does not occur in solids
• Free moving electrons

  Move more quickly and spread out in liquids compared to solids
• Less dense liquid rises, more dense liquid falls to take its place
• Radiation


  Does not involve molecules, only infrared waves
• Hotter objects emit more radiation
• Black matte surfaces

  Absorb and emit more radiation than shiny surfaces
• Eight stores of energy

  • Gravitational
  • Chemical
  • Kinetic
  • Elastic
  • Thermal
  • Magnetic
  • Electrostatic
  • Nuclear
• Thermal or Heat Energy


  Energy of an object due to its temperature
• Kinetic Energy


  Energy possessed by a moving object, increases as speed increases
• Chemical Energy


  Energy released when chemical reactions take place (e.g. in fuel, food, batteries)
• Nuclear Energy


  Energy released when nuclear reactions take place (e.g. in the sun)
• Gravitational (Potential) Energy


  Energy possessed by an object due to its position
• Elastic Energy


  Energy stored in a stretched/squashed object
• Magnetic Energy


  Energy possessed by magnetic materials
• Electrostatic Energy


  Energy possessed by electrically charged objects
• Four ways energy can be transferred

  • Mechanically
  • Electrically
  • By heating (temperature)
  • By radiation (light and sound)
• Efficiency

  Useful energy output / Total energy input x 100%
• Sankey diagrams can be used to represent the efficiency of an energy transfer