Conservation of Energy and Power

• Energy is NEVER destroyed
• Conservation of Energy Principle


  Energy can be transferred usefully, stored or dissipated, but can never be created or destroyed
• Energy transfer between stores

  1. Not all energy is transferred usefully

  2. Some energy is always dissipated
• Dissipated energy


  Energy stored in a way that is not useful (usually thermal energy)
• Energy transfers in a closed system


  1. Energy transferred from thermal energy store of soup to thermal energy store of spoon

  2. No net change in energy as no energy leaves the system
• Power


  The rate of energy transfer or the rate of doing work
• Power unit


  Watts (1 joule of energy transferred per second)
• Calculating power


  1. Power (W) = Energy transferred (J) / Time (s)

  2. Power (W) = Work done (J) / Time (s)
• Powerful machine


  • Transfers a lot of energy in a short space of time
  • Not necessarily one which can exert a strong force