physics energy

• 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
• Efficiency


  A measure of how good a device is at transferring energy input to useful energy output

  
• Total input energy


  The total amount of energy supplied to a device
• Useful energy output


  The amount of energy that is transferred to useful energy stores
• Wasted energy output

  The amount of energy that is wasted or dissipated to the surroundings
• Efficient device


  A device that wastes very little of its input energy
• Inefficient device


  A device that wastes most of its input energy
• Efficiency = useful output energy transfer ÷ total input energy transfer


  The equation linking efficiency, useful output energy transfer and total input energy transfer
• Efficiency = useful power output ÷ total power input


  The equation linking efficiency, useful power output and total power input
• Percentage efficiency

  Found by multiplying the efficiency by 100
• What is meant by an efficiency greater than 1 or 100%

  More energy is being transferred than is being supplied
• Why can't you have an efficiency greater than 1 or 100%

  This would would break the law of conservation of energy as it would mean that energy is being created
• Reasons devices waste energy

  1) Friction between their moving parts2) Heat due to electrical resistance3) Unwanted sound or light
• (higher-tier only) How to improve efficiency

  Reduce the amount of energy that a device wastes or dissipates to the surroundings
• (higher-tier only) Ways to improve efficiency

  1) Lubricate mechanical devices to reduce the friction between moving parts of the machine2) Insulate heating devices to reduce the dissipation of thermal energy to the surroundings