Energy

• Energy


  Never created or destroyed, only transferred between different energy stores and between objects
• Energy stores


  • Thermal energy stores
  • Kinetic energy stores
  • Gravitational potential energy stores
  • Elastic potential energy stores
  • Chemical energy stores
  • Magnetic energy stores
  • Electrostatic energy stores
  • Nuclear energy stores
• Energy transfer


  1. Transferred mechanically (by a force doing work)

  2. Transferred electrically (work done by moving charges)

  3. Transferred by heating

  4. Transferred by radiation (e.g. light, sound)
• System


  A single object or a group of objects that you're interested in
• 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 transferred to the thermal energy store of an object (causing its temperature to rise)
• Energy transfer by doing work

  Work done causes energy transfer from one energy store to another (e.g. chemical energy store to kinetic energy store)
• Falling objects transfer energy from gravitational potential energy store to kinetic energy store
• Kinetic energy


  Energy an object has due to its motion
• Gravitational potential energy


  Energy an object has due to its position in a gravitational field
• Elastic potential energy


  Energy stored in an object when it is stretched or compressed
• Specific heat capacity


  The amount of energy needed to raise the temperature of 1kg of a substance by 1°C
• Different materials have different specific heat capacities
• Investigating specific heat capacity

  1. Measure mass of material

  2. Insulate material

  3. Measure initial temperature

  4. Apply power and measure temperature increase

  5. Calculate energy transferred and plot graph

  6. Find gradient of graph to determine specific heat capacity
• Conservation of energy


  Energy is always conserved, it can only be transferred or dissipated, never created or destroyed
• 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
• System


  A closed system where energy is transferred within the system but no energy leaves the system
• Energy transfer in a closed system


  1. Energy transferred from thermal energy store of soup to thermal energy store of spoon

  2. Net change in energy is zero
• Power


  • Measured in watts (1 joule of energy transferred per second)
  • Can be calculated using the equations: Power (W) = Energy transferred (J) / Time (s) or Power (W) = Work done (J) / Time (s)
• A powerful machine is one which transfers a lot of energy in a short space of time
• Conduction


  The process where vibrating particles transfer energy to neighbouring particles
• Conduction


  1. Energy transferred to an object by heating is transferred to the thermal store of the object

  2. Particles in the heated part vibrate more and collide, transferring energy between their kinetic energy stores

  3. Process continues until energy is transferred to the other side of the object and then to the surroundings
• Thermal conductivity


  A measure of how quickly energy is transferred through a material by conduction
• Convection


  Where energetic particles move away from hotter to cooler regions
• Convection


  1. Energy transferred by heating to the thermal store of the liquid or gas

  2. Heated particles move faster and the space between them increases, causing the density to decrease

  3. Warmer, less dense region rises above cooler, denser regions
• Denser materials are better thermal conductors than less dense materials
• Lubrication


  Reduces frictional forces between moving surfaces
• Insulation


  Reduces the rate of energy transfer by heating
• Insulation methods


  • Cavity walls with air gap
  • Loft insulation with fibreglass wool
  • Double-glazed windows with air gap
• Draught excluders around doors and windows reduce energy transfers by convection
• Efficiency


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


  Efficiency = Useful output energy transfer / Total input energy transfer x 100

  Efficiency = Useful power output / Total power input
• No device is 100% efficient, with the wasted energy usually transferred to useless thermal energy stores
• Electric heaters are 100% efficient as all the energy in the electrostatic energy store is transferred to useful thermal energy stores
• Ultimately, all energy ends up transferred to thermal energy stores
• Non-renewable energy resources


  • Fossil fuels (coal, oil, natural gas)
  • Nuclear fuels (uranium, plutonium)
• Renewable energy resources


  • Solar
  • Wind
  • Water waves
  • Hydroelectricity
  • Biofuel
  • Tides
  • Geothermal