energy

• a system is an object or group of objects
• There are changes in the way energy is stored when a system changes.
• The specific heat capacity of a substance is the amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius.
• Power is defined as the rate at which energy is transferred or the rate at which work is done.
• Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed.
• dissipated energy is often described as being ‘wasted’.
• The higher the thermal conductivity of a material the higher the rate of energy transfer by conduction across the material.
• The main energy resources available for use on Earth include: fossil fuels (coal, oil and gas), nuclear fuel, bio-fuel, wind, hydro-electricity, geothermal, the tides, the Sun and water waves.
• A renewable energy resource is one that is being (or can be) replenished as it is used.
• The uses of energy resources include: transport, electricity generation and heating.
• What is energy transferred between stores?

  Energy is transferred between different energy stores
• What are the types of energy stores?

  1. Thermal energy stores
  2. Kinetic energy stores
  3. Gravitational potential energy stores
  4. Elastic potential energy stores
  5. Chemical energy stores
  6. Magnetic energy stores
  7. Electrostatic energy stores
  8. Nuclear energy stores
• What does the term "system" refer to in energy transfer?

  A system refers to an object or group of objects
• What happens when a system changes?

  Energy is transferred between objects or stores
• What is a closed system?

  A closed system cannot exchange matter or energy
• What does "work done" mean in terms of energy?

  Work done is energy transferred
• How can work be done in a system?

  By current flow or moving an object
• What is the formula for kinetic energy?

  Kinetic energy = $\frac{1}{2} \text{mass} \times \text{speed}^2$
• What is the formula for gravitational potential energy?

  Gravitational potential energy = mass x gravitational field strength x height
• What is the formula for elastic potential energy?

  Elastic potential energy = $\frac{1}{2} \text{spring constant} \times \text{extension}^2$
• What is specific heat capacity?

  • Different materials have different specific heat capacities
  • More energy is needed to raise temperature in some materials
  • Specific heat capacity measures energy needed to raise 1kg by 1 degree
• What is the formula for change in thermal energy?

  Change in thermal energy = mass x specific heat capacity x temperature change
• What is the conservation of energy principle?

  • Energy can be transferred and stored
  • Energy can never be created or destroyed
  • Some energy is always dissipated during transfer
• What is power in terms of energy transfer?

  Power is the rate of energy transfer
• How is power measured?

  Power is measured in watts
• What is one watt equivalent to?

  One watt = one joule per second
• What is the formula for power?

  Power = energy transferred divided by time
• What is another formula for power?

  Power = work done divided by time
• What is conduction?

  • Conduction occurs mainly in solids
  • Vibrating particles transfer energy to neighboring particles
  • Energy is shared across kinetic energy stores of particles
• What is thermal conductivity?

  • Thermal conductivity measures energy transfer speed
  • Higher thermal conductivity means faster energy transfer
• What is convection?

  • Convection occurs in liquids and gases
  • Energetic particles move from hotter to cooler regions
  • Warmer, less dense regions rise above cooler regions
• How can unwanted energy transfers be reduced?

  • Lubrication reduces frictional forces
  • Insulation reduces energy transfer by heating
• What are methods to prevent heat loss in houses?

  • Cavity walls reduce conduction
  • Loft insulation reduces conduction and convection
  • Double-glazed windows prevent conduction
  • Draught excluders prevent conduction
• What is efficiency in energy transfers?

  • Efficiency measures useful energy output vs. total input
  • Less wasted energy means higher efficiency
• What is the formula for efficiency?

  Efficiency = useful output energy / total input energy
• What is another formula for efficiency?

  Efficiency = useful power output / total power input
• What are non-renewable energy resources?

  • Non-renewable resources will eventually run out
  • Include fossil fuels and nuclear fuels
  • Fossil fuels form underground over millions of years
• What are renewable energy resources?

  • Renewable resources will never run out
  • Include solar, wind, hydro-electric, bio-fuel, tides, geothermal
  • Can be renewed as they are used
• What are the environmental impacts of renewable energy sources?

  They are less damaging than non-renewable sources
• What is wind power?

  Wind power involves many wind turbines