Topic 8 Energy: Forces Doing Work

• What is the principle regarding the creation and destruction of energy?

  Energy is never created or destroyed; it is only transferred.
• What happens to energy when a system changes?

  Energy is transferred from one form to another.
• In what form does electrical energy change in a motor?

  Electrical energy changes into kinetic energy.
• What is a closed system?

  A closed system is one that experiences no external forces.
• Can you give an example of a closed system?


  Examples include a circuit or a skydiver.
• What remains constant in a closed system?

  The total energy remains the same at all times.
• What is the formula for change in gravitational potential energy?


  ∆GPE = mgh
• What does each variable in the gravitational potential energy formula represent?

  m is mass (kg), g is gravitational field strength (N/kg), and h is change in vertical height (m).
• What does each variable in the kinetic energy formula represent?

  m is mass (kg) and v is speed (m/s).
• What is work done in terms of energy transfer?

  Work done is when an external force transfers energy to a system.
• Can you provide an example of work done?


  A human doing work to push a ball up a hill.
• How does chemical potential energy relate to electric energy?

  Chemical potential energy stored in batteries forms electric energy.
• How does electric energy transfer to thermal energy?

  Electric energy transfers to thermal energy as work is done against heating coils.
• What is the formula for work done?


  Work done = Fd
• What do the variables in the work done formula represent?


  F is force (N) and d is distance moved in the direction of the force (m).
• Why is energy rarely 100% transferred into the desired form?

  Some energy is dissipated and stored in less useful ways.
• What causes mechanical processes to be wasteful?

  Mechanical processes are wasteful when they get hot, usually due to friction.
• What happens to energy when it is dissipated as heat?

  Energy is lost to the surroundings.
• What is power in terms of energy transfer?

  Power is the rate at which energy is transferred.
• What is the formula for power?

  P = \frac{E}{t}
• What do the variables in the power formula represent?

  E is energy transferred or work done (J) and t is time taken (s).
• How is 1 Watt defined?

  1 Watt is equal to 1 Joule per second.
• What does efficiency measure?

  Efficiency measures how much energy is not lost as waste.
• What is the formula for efficiency?

  Efficiency = \frac{\text{useful output energy}}{\text{total input energy}}
• What are the key concepts related to energy transfer?

  • Energy is never created or destroyed, only transferred.
  • Energy changes form during system changes.
  • Closed systems maintain constant total energy.
  • Work done transfers energy to a system.
  • Energy is rarely 100% transferred; some is dissipated.
  • Power is the rate of energy transfer.
  • Efficiency measures energy loss as waste.