Energy Stores and Transfers

• Energy stores:

  • Kinetic
  • Gravitational potential
  • Elastic potential
  • Thermal
  • Chemical
  • Nuclear
  • Magnetic
  • Electrostatic
• Energy transfers:

  • Heating
  • Waves
  • Electric current
  • Mechanically
• A system is an object or a group of objects.
• A closed system is a system where no energy can be transferred to or from the surroundings - the total energy in the system stays the same.
• Work done is the energy transferred when a force moves an object.
• The unit for energy is joules (J).
• One joule of work is the work done when a force of 1N causes an object to move 1m in the direction of the force.
• Energy transfer of a car slowing down:

  Energy is transferred mechanically from the kinetic store of the car to the thermal store of its brakes - some energy is dissipated to the thermal store of the surroundings.
• Energy transfer of a kettle:

  The electric current in a kettle transfers energy to the heating element's thermal store - energy is then transferred by heating from the heating element's thermal store to the thermal store of the water.
• Energy transfer of a ball fired by an elastic band:

  Energy is transferred mechanically from the store of the elastic store of the elastic band to the kinetic store of the band and then the kinetic store of the ball - some energy is dissipated to the thermal store of the surroundings.
• Energy transfer of an apple hitting the ground:

  Energy is transferred from the gravitational potential store of the apple to the kinetic store of the apple - energy is then transferred from the kinetic store of the apple and dissipated to the thermal store of the surroundings by sound waves.
• Watt (W) is one joule of energy transferred per second.
• Thermal conductivity is how well a material or substance can conduct heat.
• Thermal insulators have low thermal conductivity.
• Rate of thermal energy transfer factors:

  • Thermal conductivity of material.
  • Temperature difference.
  • Thickness of material.
• Factors effecting heat loss from a building:

  • Thickness of walls and roof.
  • Thermal conductivity of walls and roof.
  • The temperature difference between the two sides of wall/roof.