Energy (pg. 39-47)

• Energy stores:

  1. Kinetic.
  2. Thermal.
  3. Chemical.
  4. Gravitational potential.
  5. Elastic potential.
  6. Electrostatic.
  7. Magnetic.
  8. Nuclear.
• Four ways to transfer energy:

  1. Mechanically - an object moving due to a force acting on it.
  2. Electrically - a charge moving through a potential difference.
  3. By heating - energy transferred from a hotter object to a colder object.
  4. By radiation - energy transferred by light/ sound waves.
• Energy can be stored, transferred between stores, and dissipated - but it can never be created or destroyed. The total energy of a close system has no net change.
• Energy is only useful when it is transferred from one store to a useful store.
• total energy input = useful energy output + wasted energy
• efficiency = useful energy output / total energy output x 100
• Thermal radiation is the transfer of energy by heating by infrared electromagnetic waves.
• Energy can be transferred by heating through radiation, conduction, and convection.
• Conduction and convection are energy transfers that involve the transfer of energy by particles.
• Conduction is the main form of energy transfer by heating in solid.
• Convection is the main form of energy transfer by heating in liquids and gases.
• Thermal conduction is the process where vibrating particles transfer energy from their kinetic energy store to the kinetic energy stores of neighboring particles.
• Convection occurs when the more energetic particles move from the hotter region to the cooler region - and transfer energy as they do.
• Materials with a high thermal conductivity transfer energy between their particles quickly.
• Insulation works by trapping pockets of air which can't move, so the energy has to conduct very slowly through the pockets of air.
• A black and dull surface is better at absorbing and emitting radiation than a white and shiny one.
• When a force moves an object through a distance, work is done on the object and energy is transferred.
• Work done = Force x Distance moved
• Power = Work done / Time taken
• Power is the rate at which energy is transferred.
• 1 W = 1 J of energy transferred per second (J/s).
• $KE =$$1/2mv²$
• $GPE =$$mgh$
• For a falling object when there's no air resistance:

  Energy lost from the g.p.e store = Energy gained in the kinetic energy store