efficiency and energy resources

• What happens to mechanical processes when they cause a rise in temperature?

  They become wasteful
• What often causes waste in mechanical processes?

  Friction
• What effect does friction have on energy?

  It transfers energy by heating
• How is wasted energy defined?

  Energy that is not useful for its purpose
• What is the term for energy transferred to the surroundings?

  Dissipated energy
• What is useful energy?

  • Energy transfer serving an intended purpose
• What is wasted energy?

  • Energy transfer not useful for its purpose
  • Dissipated to the surroundings
• What type of energy does a moving bat have?

  Kinetic energy
• What happens to some energy when a bat hits a ball?

  It is transferred to the ball's kinetic store
• How is energy dissipated when a bat hits a ball?

  By heating to the bat, ball, and surroundings
• What is the useful energy transfer in an electric motor lifting a load?

  Energy to the gravitational potential store
• What causes wasted energy in an electric motor?

  Friction between components causing heating
• What are examiner tips for identifying energy transfers?

  • Identify "useful" and "wasted" energy transfers
  • Use the term 'dissipated to the surroundings'
• What is dissipation of energy?

  Energy spreading out to the surroundings
• Why is dissipated energy difficult to gather?

  It becomes less useful
• What is wasted energy transfer in a television?

  Energy to the thermal store dissipated by heating
• What is the useful energy transfer in a heater?

  Energy to the thermal store of the heating element
• What is the wasted energy transfer in a heater?

  Energy dissipated as visible light
• What are common situations where energy transfers are unwanted?

  • Keeping a house warm
  • Keeping drinks hot or cold
  • Friction of mechanical parts
• Why is it expensive to run heating appliances?

  They require a lot of energy
• What contributes to global warming from energy production?

  Greenhouse gases from fossil fuels
• How can wasted energy transfers be reduced?

  By preventing or reducing unwanted energy transfers
• What is lubrication used for in machines?

  To reduce friction and wasted energy
• How does insulation affect energy transfers?

  It reduces energy transfers from conduction
• What factors affect the effectiveness of an insulator?

  Thermal conductivity, density, and thickness
• What is thermal conduction?

  Energy transfer by vibrating particles
• What direction does energy transfer occur in thermal conduction?

  From hot to cold
• What happens to objects during thermal equilibrium?

  They reach equal temperature with surroundings
• What materials are good thermal conductors?

  Metals
• What are poor conductors called?

  Insulators
• What factors affect thermal conduction?

  Thickness, thermal conductivity, temperature difference
• How can the rate of energy transfer be reduced?

  By increasing thickness and decreasing conductivity
• What is efficiency in energy transfers?

  • Measure of wasted energy in a system
  • Ratio of useful energy output to total energy output
• How is efficiency represented?

  As a decimal or percentage
• What is the equation for efficiency?

  Efficiency = useful energy output / total energy output
• How do you calculate the percentage efficiency of a motor?

  Efficiency = (useful energy / total energy) × 100
• If a motor transfers 300 J and wastes 85 J, what is the useful energy transferred?

  215 J
• What is the percentage efficiency if a motor transfers 300 J and wastes 85 J?

  71.67%
• What is the conservation of energy principle?

  • Energy cannot be created or destroyed
  • Total energy input equals total energy output
• What is the total energy transferred by the device (output)?

  300 J