Topic 1 - energy

• Energy is never created or destroyed.
• The 8 energy stores:

  1. Thermal
  2. Kinetic
  3. Gravitational potential
  4. Elastic potential
  5. Chemical
  6. Magnetic
  7. Electrostatic
  8. Nuclear
• Energy is transferred:

  1. Mechanically (a force doing work)
  2. Electrically (electrical currents)
  3. Heating
  4. Radiation (light or sound)
• A kettle's energy transfers:

  1. Electrical energy from the plug flows to the heating element of the kettle
  2. This energy is transferred electrically to the thermal energy store of the heating element
  3. The heating element transfers the energy to the water's thermal energy store
  4. The kettle boils
• Work done can be mechanical or electrical.
• Kicking a ball (work done): energy from the chemical energy store of your leg is transferred to the kinetic energy store of the ball.
• Electrical work done: the energy required to overcome the resistance in wires.
• A vehicle breaking:

  1. Friction is created between the brakes and the wheels
  2. The friction has done work
  3. The energy in the wheels kinetic energy stores is transferred to the thermal energy stores of the surroundings
• Kinetic energy = 1/2mv²
• weight = mass x gravity
• G.P.E = mass x gravity x height
• Elastic potential energy = 1/2 x spring constant x extension²
• change in internal energy = mass x specific heat capacity x temperature change
• Specific heat capacity is the amount of energy needed to raise the temperature of 1kg of a substance by 1 °C.
• Conservation of energy - energy can be transferred usefully, stored or dissipated, but can never be created or destroyed.
• An open system can exchange energy and matter with its surroundings.
• A closed system cannot exchange energy or matter with its surroundings.
• Conduction is the process of vibrating particles transferring energy to neighbouring particles.
• Thermal conductivity is a measure of how quickly heat is transferred through a material via conduction.
• Materials with a high thermal conductivity transfer energy between their particle quickly.
• Convection is where energetic particles move away from hotter to cooler regions.
• Conduction happens in solids.
• Convection happens in fluids (gases and liquids).
• An example of convection currents is radiators.

  
• Reducing energy/heat loss:

  1. Lubricant on bikes, cars - to reduce frictional forces
  2. Cavity walls - air gap to reduce conduction and foam to reduce convection
  3. Double glazing - reduces conduction
  4. Draught excluders - reduces convection
• power = energy / time
• power = work done / time
• Power is the rate at which energy is transferred, or the rate at which work is done.
• Work done is used to describe the energy transferred by a force moving an object over a certain distance.
• 1Mj = 1,000,000 joules
• Efficiency = useful energy output / total energy input
• Efficiency = useful power output / total power input
• An electric heater would be the only device that is 100% efficient.
• Oil is used for transport.
• Natural gas is burnt for domestic uses (e.g. cooking and heating).
• Coal is used in fires to heat homes.