Energy

• Open system

  Matter of the system can exchange energy with the outside world
• Closed system


  Separate from the outside world, neither matter nor energy can enter or leave
• Energy stores

  • Thermal or internal energy
  • Kinetic energy
  • Gravitational potential energy
  • Elastic potential energy
  • Chemical energy
  • Magnetic energy
  • Electrostatic energy
  • Nuclear energy
• Mechanical work done

  • Using a force to move an object, like kicking a ball up in the air
• Kettle example

  • Electrical energy from the plug socket flows to the heating element, then to the water's thermal energy store
• Work done


  Energy transferred, two main types: mechanical and electrical
• Energy can be transferred within a closed system, but the overall change is always zero
• Train example

  • Friction between brakes and wheels slows the train down, transferring energy from the wheel's kinetic energy store to the thermal energy stores of the surroundings
• Work done


  Energy transferred to an object, stored in one of the object's energy stores
• Energy transfer methods

  1. Mechanically

  2. Electrically

  3. By heating

  4. By radiation
• Energy transfer

  Energy is transferred between different forms
• Energy


  Never created or destroyed, only transferred between different forms and objects
• Forms of energy

  • Thermal or internal energy
  • Kinetic energy
  • Gravitational potential energy
  • Elastic potential energy
  • Chemical energy
  • Magnetic energy
  • Electrostatic energy
  • Nuclear energy
• System


  Collection of matter in physics where energy is transferred between objects or between different forms
• Electrical work done

  • Current flowing, overcoming resistance in wires of a circuit
• Calculation example: LED lamp is 5 times more efficient than incandescent bulb
• Energy output forms from a lamp

  • Light energy
  • Heat energy
• Efficiency can be calculated as a decimal or a percentage
• Efficiency equation: efficiency equals useful energy output divided by total energy input
• Efficiency equation for power: efficiency equals useful power output divided by total power input
• Efficiency is the proportion of the energy supplied that is actually transferred into the useful energy output
• Most devices aren't 100% efficient in transferring energy
• Energy can be transferred from one form into another form
• Conservation of energy principle: energy can only be transferred, never created or destroyed
• Common mistake in efficiency calculation: getting the division the wrong way around
• No device is 100% efficient as all devices produce some form of waste energy
• Exception to efficiency rule: devices whose function is to produce heat in the first place
• Power efficiency calculation

  1. Rearrange efficiency equation to get useful power output by itself

  2. Convert efficiency into a decimal

  3. Plug values into the equation to calculate useful power output
• Efficiency calculation

  1. Efficiency equals useful energy output divided by total energy input

  2. Efficiency equals useful power output divided by total power input
• New generation of renewable resources

  • Solar
  • Wind
  • Hydroelectric
  • Geothermal
  • Biofuels
  • Tidal
• Non-renewable energy resources are referred to as fossil fuels and nuclear energy
• Non-renewable energy resources


  • Coal
  • Oil
  • Natural gas
• In the UK, most energy is used for transport or domestic uses
• Solar water heaters use the sun's energy to heat water for domestic use
• Transport energy sources

  • Petrol
  • Diesel
  • Kerosene
• Electricity can be renewable or non-renewable depending on how it's made
• Many people in developing countries still rely on wood as their primary form of energy
• Throughout most of human history, humans' primary source of energy was wood, which was burned to keep warm and cook food
• Trains were traditionally powered by coal, but now most are powered by electricity
• In the past 50 years, there has been a massive rise in the use of a new generation of renewable resources