P1.3

• work done = energy transferred
• Work done


  when a force makes the object move
• Work Done Equation

  Work Done = Force X Distance
• distance = work/force
• Energy is NEVER destroyed
• Energy transfer

  1. Energy can be transferred usefully

  2. Energy can be stored

  3. Energy can be dissipated
• When energy is transferred between stores, not all of the energy is transferred usefully into the store you want it to go to
• Dissipated energy


  Energy that is being stored in a way that you don't want it to go to (usually thermal energy)
• In a closed system, energy transfers occur but the net change in energy is zero
• Power


  The rate at which energy is transferred
• Power


  The rate at which work is done
• Calculating power (energy transfer)

  Power = Energy transferred / Time taken
• Calculating power (work done)

  Power = Work done / Time taken
• Work done is a special measure of the energy transferred when a force is used to move an object by a certain distance
• Energy transferred and work done are measured in joules, time is measured in seconds, and power is measured in watts
• Lamp 1 transfers 1200 joules over 20 seconds

  Power = 1200 joules / 20 seconds = 60 watts
• Lamp 2 transfers 1500 joules over 30 seconds

  Power = 1500 joules / 30 seconds = 50 watts
• The left lamp is more powerful
• Calculating energy transferred by a 1100 watt microwave in 3 minutes

  Energy transferred = Power x Time

  Energy transferred = 1100 watts x 180 seconds = 198,000 joules = 198 kilojoules
• Calculating power used to push a car 9 kilojoules over 20 seconds


  Power = Work done / Time taken

  Power = 9,000 joules / 20 seconds = 450 watts
• • Frictional forces result in more work done
  • Friction results in thermal energy
  • Thermal energy results in a rise in temperature