Conservation of Energy

• Gravitational potential energy (GPE)


  ∆GPE = mg∆h
• Gravitational potential energy (GPE)

  • Change in gravitational potential energy (joule, J) = mass (kilogram, kg) × gravitational field strength (newton per kilogram, N/kg) × change in vertical height (metre, m)
• Kinetic energy (KE)


  KE = 1/2 mv^2
• Kinetic energy (KE)


  • Kinetic energy (joule, J) = ½ x mass (kilogram, kg) × (speed)2 (metre/second2, m/s2)
• Energy transfer diagrams


  1. Show energy input

  2. Show energy output

  3. Show the forms that the energy takes

  4. Show the waste output energy
• Energy changes


  1. Object projected upwards: KE transferred to GPE, then vice versa as it falls back down

  2. Object projected up a slope: KE transferred to GPE (and also to heat if friction is present)

  3. Moving object hitting an obstacle: KE transferred to sound / KE transferred to obstacle if that moves too

  4. Object being accelerated by a constant force: Object is having work done to it, with it gaining KE, whatever supplies the force is having its energy transferred to KE

  5. Vehicle slowing down: KE transferred to heat (through brakes)

  6. Boiling water in kettle: Electrical energy to thermal
• Conservation of energy


  In physics, conservation of energy means that the total energy of an isolated system remains constant
• Closed system


  • No external forces acting on it (e.g. no change in gravitational force, no electrostatic attraction, no external magnetic force etc.)
  • In a closed system, the total energy in the system never changes, regardless of the energy transfers that take place
  • In a closed system no energy is lost
• Open system


  Energy can be transferred out of the system, and therefore the total energy of the system can change
• Mechanical waste energy


  • Energy transferred to it can cause a rise in temperature
  • Energy is dissipated to surroundings (heat is transferred to air)
  • This makes the process wasteful
• Reducing mechanical waste energy

  1. Lubricate systems, so less friction and less heat created

  2. Thermal insulation, so less heat is lost to surroundings
• Reducing heat loss in buildings

  1. Thicker walls mean greater thermal insulation, so less heat is lost

  2. Air cavities between walls causes lots of heat loss by convection - cavity wall insulation fills in this gap and prevents air flow
• Efficiency


  Ratio of useful output over total input of energy
• Increasing efficiency


  1. Reducing waste output (via lubrication/thermal insulation or other methods)

  2. Recycling waste output and using it as input (absorbing heat energy dissipated and used to as input heat energy)

  3. Suitable methods depend on each situation
• Energy sources


  • Fossil Fuels
  • Nuclear Fuel
  • Bio-Fuel
  • Wind
  • Hydro-electricity
  • Tidal
  • Solar
• Non-renewable energy is used more for large-scale energy supplies due to the large energy output per kilogram of fuel – renewable resources cannot provide such a large amount of energy as easily
• Renewable energy has become more important due to the finite lifetime of fossil fuels, and so their development has become more important
• Patterns and trends in the use of energy resources

  1. During industrial revolution, fossil fuels became an important source of energy as it was easy to mine, and provided a lot of energy

  2. Only recently has renewable energy become more suitable – technology has had to develop a lot since industrial revolution to be able to harness such energy sources efficiently