P1: conservation and dissipation of energy

• Energy stores that could come up in the GCSE syllabus

  • Gravitational
  • Elastic
  • Electrostatic
  • Chemical
  • Thermal
  • Sound
  • Nuclear
  • Light
• Energy can interchange between these different forms, but energy is always conserved - it cannot be created or destroyed, only changed in form
• Energy changes in a swing set

  1. Gain gravitational potential energy

  2. Convert to kinetic energy

  3. Lose energy to friction (thermal)

  4. Possibly some sound energy
• Energy changes in an iPod

  1. Chemical energy in battery

  2. Convert to sound

  3. Convert to light

  4. Produce thermal energy
• Energy changes in an electric kettle


  1. Electrical energy from mains

  2. Convert to thermal energy

  3. Possibly some sound energy
• Sankey diagram


  Quantitative representation of energy changes, with size of arrows representing amount of energy
• Efficiency


  Useful energy output divided by total energy input, can be expressed as a percentage
• Work done


  Energy transferred when a force causes an object to move, calculated as force x distance
• Calculation triangle for work done

  • Work done = Force x Distance
  • Distance = Work done / Force
  • Force = Work done / Distance
• Gravitational potential energy (GPE)

  Energy stored due to an object's position in a gravitational field, calculated as mass x gravity x height
• Calculation triangle for GPE

  • GPE = Mass x Gravity x Height
  • Mass = GPE / (Gravity x Height)
  • Gravity = GPE / (Mass x Height)
  • Height = GPE / (Mass x Gravity)
• Kinetic energy (KE)


  Energy of motion, calculated as 1/2 x mass x velocity^2
• Calculation triangle for KE


  • KE = 1/2 x Mass x Velocity^2
  • Mass = 2 x KE / Velocity^2
  • Velocity = sqrt(2 x KE / Mass)
• Elastic potential energy


  Energy stored in a stretched or compressed object, calculated as 1/2 x spring constant x extension^2
• Calculation triangle for elastic potential energy

  • Elastic potential energy = 1/2 x Spring constant x Extension^2
  • Spring constant = Elastic potential energy / (1/2 x Extension^2)
  • Extension = sqrt(2 x Elastic potential energy / Spring constant)
• Power


  Rate of energy transfer, measured in watts (joules per second)
• Calculation triangle for power

  • Power = Energy transfer / Time
  • Time = Energy transfer / Power
  • Energy transfer = Power x Time
• Efficiency = Useful power output / Total power input