Topic 8: Energy - Forces Doing Work

• What is the principle of the conservation of energy?

  Energy cannot be created or destroyed
• Give examples of ways energy can be transformed

  • Heating
  • Electrical work
  • Waves
  • Mechanical work
• What is the Equation for Change in Gravitational Potential Energy?

  Change in Gravitational Potential Energy (J) = mass (kg) $\times$ gravitational field strength (N/kg) $\times$ change in height (m)

  $\Delta GPE=$$\ mg\Delta h$
• What is the Equation for Kinetic Energy?

  Kinetic Energy = 1/2$\times$mass (kg)$\times$speed$^2$(m/s)

  $KE=$$\frac{1}{2}mv^2$
• What is a Closed System?

  A system which experiences no external forces
• Work Done is the Same as Energy Transferred
• What is the Equation for Work Done?

  • Work done (J) = Force (N) $\times$ Distance (m)
  • $E=$$F\times d$
• What is Work Done?

  Energy transferred by an external force to a system
• Energy is rarely transferred 100% efficiently into its desired form.

  • Some energy is dissipated - stored in less useful ways

  Mechanical processes are wasteful when they get hot (usually due to friction)

  • Energy is dissipated as heat, causing a rise in temperature
  • Energy is lost to the surroundings
• What is Power?

  The rate at which energy is transferred
• What is the Equation for Power?

  • Power (W) = Work done (J) $\div$ Time taken (s)
  • $P\ =$$\ \frac{E}{t}$
• Other than Watts (W) what are the Other Units for Power?

  Joules per second (J/s)
• What is the Equation for Efficiency?

  Efficiency = $\frac{Useful\ Output\ Energy}{Total\ Input\ Energy}$