Energy stores and systems

• A system is


  an object or a group of objects
• a closed system is

  a system where no energy can enter or leave
• kinetic energy =


  0.5 × mass × speed ^2
• gravitational potential energy =


  mass × gravitational field strength × height
• equation linking energy, power and time


  power = energy/timeP = e/t
• equation linking power, work done and time

  power = work done / timeP = W / t
• An energy transfer of 1 joule per second is equal to

  a power of 1 watt
• Law of Conservation of Energy

  Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed
• kinetic energy


  the energy stored in a moving object
• gravitational potential energy


  the energy stored due to an object's position above ground
• elastic potential energy


  the energy stored in a stretched spring
• thermal energy


  the energy stored due to an object's temperature
• as a ball moves downwards, energy is transferred

  from the gravitational potential energy store to the kinetic energy store
• as a ball moves upwards, energy is transferred

  from the kinetic energy store to the gravitational potential energy store
• Friction causes energy to be transferred to

  thermal energy
• If friction heats up the air particles, the energy has been

  dissipated (wasted)
• we can reduce unwanted energy transfers by

  reducing friction
• We can reduce friction by...

  using a lubricant on the fixed pointremoving the air particles from around the source of friction