Energy

• Define 'energy'.

  A property that can be transferred in order to perform work or cause heating effects.
• State the 8 energy stores.

  • chemical
  • kinetic
  • gravitational
  • thermal
  • elastic
  • magnetic
  • electrostatic
  • nuclear
• Name 4 energy pathways

  • heating
  • electrical
  • radiation
  • mechanical
• Define 'system'

  An object or group of objects that interact.
• Define 'open system'

  A system in which energy and matter can enter and exit e.g a cup of tea.
• Define 'closed system'

  A system in which energy can enter and leave, but matter cannot e.g a cup of tea with a lid
• Define 'isolated system'

  A system in which neither energy or matter can enter or exit e.g the universe
• State the law of energy conservation

  Energy cannot be created or destroyed, it can only be stored, transferred between energy stores or dissipated.
• State the units used to measure energy

  J/Joules
• State why energy transfer is equivalent to work done

  Because work must be done to transfer energy from one store to another
• State why energy is stored in a kinetic energy store

  When an object with mass is moving
• Write the equation that links kinetic energy, mass and velocity

  Kinetic energy = 0.5 x mass x (velocity)2
• Name two factors that affect the energy stored in the kinetic store of an object

  mass and velocity (speed)
• Does mass or velocity have a greater impact on the energy stored in the kinetic store?

  The velocity because it's squared
• What is an elastic object?

  An object that returns to its original shape and size when a force has been removed
• When is energy stored in the elastic potential energy store?

  When an object has been deformed (stretched or compressed)
• Write the equation linking elastic potential energy, spring constant and extension

  Elastic potential energy = 0.5 x spring constant x (extension)2
• State what is meant by 'extension'

  The change in length e.g new length - original length
• Name two factors that affect the energy stored in an elastic potential store

  • spring constant
  • extension
• Does extension or spring constant have a greater impact on the energy in the elastic potential energy store?

  Extension because it's squared
• State when is energy stored in a gravitational potential energy store

  When an object with mass is raised above ground level
• Write the equation linking gravitational potential energy (Ep), mass, gravity and height

  Ep = mass x gravitational field strength x height
• Why when we calculate energy transferring between stores, may 100% of energy not transfer to the second store?

  Because some of the energy is dissipated to the surrounding causing an increase of energy in the thermal store of the surroundings.
• State when energy is stored in a chemical energy store

  Energy is stored in chemical bonds. Most examples include fuels such as batteries, food, petrol, wax and oil
• State when energy is stored in a thermal energy store

  When an object is at a temperature above absolute zero (-273 C)
• Define 'temperature'

  A measure of how much energy is in the thermal store of an object. It is measured in C.
• Describe how a difference in temperature causes heating affects

  Energy will move from an area of higher temperature to an area of lower temperature until both areas reach thermal equilibrium.
• Define 'thermal equilibrium'

  When the temperature is the same
• Name the process that allows heat to transfer through a solid

  Conduction
• Name the process that allows heat to transfer through a liquid or a gas

  Convection
• Name the process that allows heat to travel via waves

  Infrared radiation
• Why do metals have a greater thermal conductivity than non-metals?

  Metals contain delocalised electrons which are free to move, collide with ions and other electrons which increases the rate of energy transfer
• Why does air have a low thermal conductivity?

  Air is a gas, which contains particles arranged with lots of space in between. This decreases the rate of energy transfer as there are less collisions between particles each second.
• Define 'specific heat capacity'

  The amount of energy required to increase the temperature of one kilogram of the substance by one degree Celsius.
• Write the equation that links energy transfer, mass, specific heat capacity and change in temperature

  Change in thermal energy = mass x specific heat capacity x temperature change
• Define 'power'

  The rate at which energy is transferred (work is done)
• Write the equation that links power, energy transfer and time taken

  Power = energy transfer/time taken
• State the units used to measure power

  W/Watts
• What is a watt equivalent to?

  1 Joule per second
• What is kwh

  A unit of energy transfer