Energy

• Energy Stores


  • Thermal
  • Kinetic
  • Gravitational potential
  • Elastic potential
  • Chemical
  • Magnetic
  • Electrostatic
  • Nuclear
• Energy Transfer


  1. Mechanically (by force doing work)

  2. Electrically (work done by charges)

  3. By heating

  4. By radiation (e.g. light, sound)
• Closed systems are systems where neither matter nor energy can enter or leave
• The net change in the total energy of a closed system is always zero
• Energy Transfer by Heating


  Energy is transferred to the water's thermal energy store (causing the temperature of the water to rise)
• Energy Transfer by Doing Work


  1. Work done is just another way of saying energy transferred

  2. Work can be done when current flows (work is done against resistance in a circuit)

  3. Work can be done by a force moving an object
• Kinetic Energy


  Energy of movement
• Gravitational Potential Energy


  Energy stored in an object due to its position in a gravitational field
• Elastic Potential Energy


  Energy stored in an object due to its deformation
• Energy is never destroyed, it is only transferred or dissipated
• Dissipated Energy


  Energy that is transferred in a way that is not useful, usually to thermal energy stores
• In a closed system, the net change in energy is zero
• Power


  The rate of energy transfer or the rate of doing work
• A powerful machine transfers a lot of energy in a short space of time
• Reducing Unwanted Energy Transfers


  1. Lubrication reduces frictional forces

  2. Heating can occur by conduction and convection
• Power


  The rate at which energy is transferred or the rate at which work is done
• Both motors transfer the same amount of energy


  But one motor would do it quicker than the other
• Lubrication reduces frictional forces
• Heating can occur by conduction and convection
• Thermal conductivity


  • A measure of how quickly energy is transferred through a material
• Insulation reduces the rate of energy transfer by heating
• Efficiency


  The ratio of useful output energy transfer to total input energy transfer
• Calculating efficiency


  1. Useful output energy transfer / Total input energy transfer

  2. Useful power output / Total power input
• Renewable energy resources


  • The Sun (Solar)
  • Wind
  • Hydro-electricity
  • Bio-fuel
  • Tides
  • Geothermal
• Non-renewable energy resources


  • Fossil fuels (coal, natural gas)
  • Nuclear fuel (uranium, plutonium)
• Non-renewable energy resources will run out one day
• Renewable energy resources will never run out
• Uses of energy resources

  • Transport
  • Heating
• Non-renewable energy resources used for transport


  • Petrol and diesel powered vehicles
  • Coal-powered steam trains
• Renewable energy resources used for transport


  • Vehicles that run on bio-fuels
• Non-renewable energy resources used for heating


  • Natural gas
  • Coal
  • Electric heaters
• Renewable energy resources used for heating


  • Geothermal heat pumps
  • Solar water heaters
  • Burning bio-fuel