Efficiency

• Friction causes energy to be dissipated
• Lubrication can reduce the friction between objects and save energy
• Insulation reduces the rate of energy transfer by heating
• In a building they insulate by

  • Having thick walls made of a material with low thermal conductivity
  • Cavity walls which include an air gap
  • Loft insulation
  • Double glazed windows which have an air gap
  • Draught excluders around doors and windows
• Insulation Practical Method

  • Boil water in a kettle and the place 100cm³ into a beaker sealed with a lid and wrapped in an insulating material
  • Use a thermometer to measure the initial temperature
  • Completely seal the container then leave in a room for 5 minutes measuring the time with a stop watch
  • Remove the lid and measure the final temperature
  • Repeat the experiment with different materials as insulators
• Efficiency

  $Efficiency =$$\frac{Useful\:output\:energy\:transfer}{Total\:input\:energy\:transfer}$
• Efficiency

  $Efficiency =$$\frac{Useful\:power\:output}{Total\:power\:input}$