pmt notes - energy

• there are 8 stores of energy
• 8 stores of energy - kinetic , thermal , chemical , gravitational , elastic , nuclear , magnetic
• there are 4 pathways for energy
• energy is measured in Joules (J)
• principle of energy transfer - energy can not be created or destroyed
• fuels are a concentrated energy store
• energy can not be created or destroyed
• 3 uses of fuel - heating , cooking , powering machines
• efficiency (%) = (useful energy output/total energy input) x 100
• power (watts) = energy transferred / time taken
• law of energy conservation - energy cannot be created or destroyed
• energy can be transferred mechanically, electrically, through heating, via infrared radiation, via light or sound waves
• a system is an object or group of objects
• When a system changes the energy store also changes
• what happens what a ball is rolling and hitting a wall

  • Moving ball system
  • Kinetic energy transfers to sound
• Vehicle slowing down

  • Moving vehicle system
  • Kinetic energy transfers to thermal due to friction
• Specific Heat Capacity is the energy required to raise the temperature of 1kg of a substance by 1°C
• Power is the rate at which energy is transferred or the rate at which work is done
• Energy transfer of 1 joule per second is equal to a power of 1 watt
• The motor that can do the same work faster is more powerful
• Energy can be transferred usefully, stored or dissipated but cannot be created or destroyed
• In all system changes energy is dissipated, so that it is stored in less useful ways
• 2 ways of reducing energy waste

  • Lubrication
  • Thermal insulation
• The higher the thermal conductivity of a material, heat is allowed to travel through the material more easily, so the higher the rate of energy transfer by conduction across the material
• 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 the useful work done by a machine, engine, device, etc, to the energy supplied to it, often expressed as a percentage
  • efficiency = useful energy output

  total energy input

  = useful power output

  total power input
• Ways to increase efficiency

  • Reducing waste output
  • Recycling waste output
• Main Energy Sources

  • Non-renewable: Fossil Fuels, Nuclear Fuel
  • Renewable: Biofuel, Wind, Hydro-electricity, Geothermal, Tidal, Solar, Water waves
• Renewable energy

  Energy which can be replenished as it is used
• Non-renewable energy


  Used more for large-scale energy supplies due to the large energy output per kilogram of fuel
• Renewable energy has become more important due to the finite lifetime of fossil fuels
• Renewable energy is not always the most reliable
• Main Energy Uses

  • Transport
  • Electricity generation
  • Heating
• Environmental Impact of Energy

  • Extraction: Fossil fuels destroy landscapes, Wind turbines can be eyesores
  • Use: Fossil fuels release harmful emissions, Solar and wind create electricity with no emissions
• During industrial revolution, fossil fuels became an important source of energy as it was easy to mine, and provided a lot of energy
• 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
• It is easier to use energy resources due to increasing pressure to cope with the public's increasing power demands but harder to solve environmental issues due to political, social, ethical and economic considerations