1.7 Energy, Work and Power

• Forms of stored energy

  • Kinetic
  • Gravitational potential
  • Chemical potential
  • Elastic potential
  • Nuclear
  • Electrostatic
  • Internal (thermal)
• Energy can be transferred from one form to another during processes
• Processes for energy transfer

  • Mechanical work done (force)
  • Electrical work done (electric current)
  • Heating
  • Waves (electromagnetic, sound, etc.)
• The principle of conservation of energy states that energy cannot be created nor destroyed but can change from one form to another
• Sankey diagram


  Diagram showing the efficiency of an energy transfer process

  
• Efficiency


  Useful energy output / Total energy input
• Gravitational potential energy

  mass (kg) * gravitational field strength * height (m)
• Gravitational acceleration


  9.8 m/s2
• Calculating kinetic energy


  Ek = ½mv2
• Energy


  Joule (J)
• Calculating work done


  W = ∆E = Fd
• Work


  Joule (J)
• Calculating work done


  • A 2 kg box is pushed with a force of 60 N for 8 m. Calculate the work done on the box
  • Calculate the force needed to push a box 12 m if 600 J of work was done
• Sources of energy


  • Fossil fuels (coal, oil, gas)
  • Biofuel
  • Geothermal
  • Nuclear fuel
  • Water (hydro, wave, tidal)
  • Wind
  • Solar (light and heat)
  • Hydroelectric (water cycle)
  • Wind (convection)
  • Geothermal (Earth)
  • Nuclear (fission of atoms)
  • Tidal (Moon)
• Most energy resources come from the Sun (solar, fossil fuels, biofuels, hydroelectric, wind)
• Some energy resources do not come from the Sun (geothermal, nuclear, tidal)
• Nuclear fusion


  The process that powers the Sun
• We haven't made a nuclear fusion power plant yet, but we are working on it
• Calculating power


  Power = Work/Time = Energy/Time
• Power


  Watt (W)
• Calculating power


  • Ali has a mass of 60 kg and climbs up 5 m in 20 s. Find his power output.