Physics - Topic 8 - Energy: Forces Doing Work

• What is the principle of energy conservation?

  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 a motor, what type of energy changes into kinetic energy?

  Electrical energy
• What is a closed system?

  A system which experiences no external forces
• Give an example of a closed system.

  A circuit or a skydiver
• What remains the same in a closed system at all times?

  The total energy
• What is the formula for change in gravitational potential energy?

  ∆GPE = mg∆h
• What does the variable 'm' represent in the gravitational potential energy formula?

  Mass in kilograms (kg)
• What does 'g' represent in the gravitational potential energy formula?

  Gravitational field strength in newtons per kilogram (N/kg)
• What does '∆h' represent in the gravitational potential energy formula?

  Change in vertical height in meters (m)
• What is the formula for kinetic energy?

  KE = \frac{1}{2} mv^2
• What does 'v' represent in the kinetic energy formula?

  Speed in meters per second (m/s)
• What is work done in terms of energy transfer?

  When an external force transfers energy to a system
• Give an example of work done.

  A human pushing a ball up a hill
• What type of energy is formed from chemical potential energy in batteries?

  Electric energy
• How does electric energy transfer to thermal energy?

  As work is done against the heating coils causing them to heat up
• What is the formula for work done?

  W = Fd
• What does 'F' represent in the work done formula?

  Force in newtons (N)
• What does 'd' represent in the work done formula?

  Distance moved in the direction of the force in meters (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?

  They get hot, usually due to friction
• What happens to energy dissipated as heat?

  It causes a rise in temperature and is lost to the surroundings
• What is power in terms of energy transfer?

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

  P = \frac{E}{t}
• What does 'E' represent in the power formula?

  Energy transferred or work done in joules (J)
• What does 't' represent in the power formula?

  Time taken in seconds (s)
• How is 1 Watt defined?

  1 Joule per second
• What does efficiency measure?

  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 different forms of energy transfer mentioned?

  • Electrical energy to kinetic energy in motors
  • Chemical potential energy to electric energy in batteries
  • Electric energy to thermal energy in heating coils
  • Work done by external forces
• What are the key concepts related to energy waste and efficiency?

  • Energy is rarely 100% transferred into the desired form
  • Mechanical processes can be wasteful due to heat from friction
  • Power is the rate of energy transfer
  • Efficiency measures how much energy is not lost as waste