Energy

• Energy stores:

  SYSTEM: an object or group of objects storing energy

  • when system changes, the energy transfers
• Energy store examples:

  1 ball rolls, hits wall

  • system is the moving ball
  • hits wall: kinetic energy is transferred as sound

  2 vehicle slows down

  • system is the vehicle moving
  • when it slows down, kinetic energy transfers to thermal energy due to friction between wheels
• Kinetic energy (KE): energy that an object has because it's moving
• Elastic potential energy (EPE): energy stored when an elastic material is stretched or compressed
• Gravitational potential energy (GPE): energy stored by an object due to its height above ground level
• $kinetic=$$(1/2)mv^2$

  where m is mass in kg, v is velocity in m/s and kinetic is in joules J
• $elasticpotential=$$(1/2)ke^2$

  k is spring constant in newtons/m and e is extension in m
• $gravitational potential=$$mgh$

  g is 9.8 newtons/kg and h is height in m
• Power is the rate at which energy is transferred or the rate at which work is done.
• power = energy transferred / time

  or

  power = work done / time

  where power is in watts, work done is in joules
• work done = force x distance moved
• An energy transfer of 1 joule / s is equal to a power of 1 watt
• If given 2 motors, the motor that can do the same work faster is more powerful

  • the energy is transferred at a faster rate
• Energy can be transferred usefully, stored or dissipated

  • in all system changes energy is dissipated (wasted) so it is stored in less useful ways
• Reducing energy waste

  Lubrication

  • oil in a motor reduces friction, less energy is lost as heat through friction

  Thermal Insulation

  • double glazing means less useful thermal energy is lost
• Higher thermal conductivity of a material = higher rate of energy transfer by conduction

  THERMAL CONDUCTIVITY IN A BUILDING: rate of cooling is low if walls are thick and thermal conductivity of the walls are low

  • if the walls are thin metal sheets heat would be lost very quickly
• Efficiency: The ratio of useful energy output to total energy input

  $efficiency =$$energy output/totalenergy$
• MAIN ENERGY SOURCES

  Non-renewable

  • Fossil Fuels (coal, oil, gas)
  • Nuclear Fuel

  Renewable

  • Biofuel
  • Wind
  • Hydro-electricity
  • Geothermal
  • Tidal
  • Solar
  • Water waves
• RENEWABLE ENERGY

  • can be replenished as it is used (e.g. wind will never stop)
  • due to the finite lifetime of fossil fuels, development has become more important
  • not most reliable (solar doesn’t work at night)
• NON-RENEWABLE ENERGY

  - 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
• Main energy uses:

  • transport
  • electricity generation
  • heating
• ENVIRONMENTAL IMPACT

  • Extraction of Energy:

  • Fossil fuels involve destroying landscapes

  • Wind turbines can be considered an eyesore

  • Use of Energy Sources:

  • Fossil fuels release harmful emissions

  • Solar directly create electricity with no emissions
• PATTERNS AND TRENDS OF ENERGY USE:

  • During industrial revolution, fossil fuels became important source of energy (easy to mine, provided a lot of energy)
  • recently renewable energy become more suitable - technology has developed a lot since industrial revolution to use energy sources efficiently
  • It is easier to use energy resources due to increasing pressure to cope with the public's increasing power demands, harder to solve environmental issues due to political, social, ethical and economic
• • An open system can gain or transfer energy
  • A closed system can‘t gain or transfer energy
• ENERGY TRANSFER MECHANISMS:

  • radiation
  • heating
  • electrically
  • mechanically (manually by person)
• weight = mass x gravitational field strength
• • as an object RISES kinetic energy is converted to gravitational potential energy
  • as an object FALLS gravitational potential energy is converted to kinetic energy