P4. WORK DONE

• when is work done?

  when an object is moved over a distance by a force applied in the direction of its displacement.

  • it is said that the force does work on the object
• • When work is done on an object, energy is transferred
  • The amount of energy transferred (in joules) is equal to the work done (also in joules)

  energy transferred (J) = work done (J)
• work done = force x distance
• what is a system?

  an object or group of objects
• • When a system is in equilibrium, nothing changes, and so nothing happens
  • When there is a change to a system, energy is transferred
• what are the 4 energy transfer pathways?

  mechanical, electrical, heating and radiation
• • Sankey diagrams can be used to represent energy transfers
  • Sankey diagrams are characterised by the splitting arrows that show the proportions of the energy transfers taking place
• Total energy in, wasted energy and useful energy out shown on a Sankey diagram

  A) useful

  B) wasted

  
• • Power is defined as

  energy transferred per unit time
• $P =$$E/t =$$W/t$


  where:

  P = power (watts)

  E = energy (joules)

  W = work done (joules)

  t = time (seconds)