Energy Stores & Transfers

• Energy Stores,

  • In physics, a system is defined as:An object or group of objects
  • Defining the system, in physics, is a way of narrowing the parameters to focus only on what is relevant to the situation being observed
  • A system could be large or small, incorporating just one object, or a whole group of objects and their surroundings
• • When a system is in equilibrium, nothing changes, and so nothing happens
  • When there is a change to a system, energy is transferred
• • If an apple sits on a table, and that table is suddenly removed, the apple will fall
  • As the apple falls, energy is transferred
• Like this...

  
• • Energy is stored in objects in different energy stores
• Energy Stores Table (part 1):

  
• Energy Stores Table (part 2):

  
• Energy Transfers:

  • Energy is transferred between stores by different energy transfer pathways
  • The energy transfer pathways are:
  • Mechanical
  • Electrical
  • Heating
  • Radiation
• Energy Transfer Pathways Table:

  
• • An example of an energy transfer by heating is a hot coffee heating up cold hands
• Energy is transferred by heating from the hot coffee to the mug to the cold hands:

  
• • Sankey diagrams can be used to represent energy transfers
  • Sankey diagrams are characterised by the splitting arrows that show the proportions of the energy transfers taking place
• The different parts of the arrow in a Sankey diagram represent the different energy transfers:

  • The left-hand side of the arrow (the flat end) represents the energy transferred into the system
  • The straight arrow pointing to the right represents the energy that ends up in the desired store; this is the useful energy output
  • The arrows that bend away represent the wasted energy
• Total energy in, wasted energy and useful energy out shown on a Sankey diagram:

  
• • The width of each arrow is proportional to the amount of energy being transferred
  • As a result of the conversation of energy:

  Total energy in = Useful energy out + Wasted energy
• • A Sankey diagram for a modern efficient light bulb will look very different from that for an old filament light bulb
  • A more efficient light bulb has less wasted energy
  • This is shown by the smaller arrow downwards representing the heat energy
• Sankey diagram for modern vs. old filament light bulb: