Energy

• Types of energy store


  • Magnetic
  • Internal (thermal)
  • Chemical
  • Kinetic
  • Electrostatic
  • Elastic potential
  • Gravitational potential
  • Nuclear
• Magnetic energy store


  Energy stored when repelling poles have been pushed closer together or when attracting poles have been pulled further apart
• Magnetic energy store

  • Fridge magnets
  • Compasses
  • Maglev trains which use magnetic levitation
• Internal (thermal) energy store

  Total kinetic and potential energy of the particles in an object, in most cases this is the vibrations - also known as the kinetic energy - of particles. In hotter objects, the particles have more internal energy and vibrate faster.
• Internal (thermal) energy store

  • Human bodies
  • Hot coffees
  • Stoves or hobs
  • Ice particles vibrate slower, but still have energy
• Chemical energy store


  Energy stored in chemical bonds, such as those between molecules
• Chemical energy store


  • Foods
  • Muscles
  • Electrical cells
• Kinetic energy store


  Energy of a moving object
• Kinetic energy store


  • Runners
  • Buses
  • Comets
• Electrostatic energy store


  Energy stored when repelling charges have been moved closer together or when attracting charges have been pulled further apart
• Electrostatic energy store


  • Thunderclouds
  • Van De Graaff generators
• Elastic potential energy store


  Energy stored when an object is stretched or squashed
• Gravitational potential energy store


  Energy of an object at height
• Gravitational potential energy store

  • Aeroplanes
  • Kites
  • Mugs on a table
• Nuclear energy store

  Energy stored in the nucleus of an atom
• Energy

  A key principle in physics, as it allows work to be done
• Power


  The rate at which energy is transferred
• Efficiency

  The amount of energy that is usefully transferred
• Work


  The measure of energy transfer when a force (F) moves an object through a distance (d)
• Energy transferred = work done
• Energy transferred and work done are both measured in joules (J)
• Work done (W)

  Measured in joules (J)
• Force (F)


  Measured in newtons (N)
• Distance (d)

  Measured in metres (m)
• One joule of work is done (or one joule of energy is transferred) when a force of one newton causes a body to move through a distance of one metre
• Energy store


  The different ways in which energy can be stored, including chemical, kinetic, gravitational potential, elastic potential and thermal stores
• Energy transfer

  The different ways in which energy can be transferred from one store to another includes heating, by waves, electric current or by a force moving an object
• Energy can be described as being in different 'stores'. It cannot be created or destroyed but it can be transferred, dissipated or stored in different ways
• Energy transfers are going on all the time - whenever a system changes there is a change in the way some or all of the energy is stored
• Examples of energy transfers

  • Mechanical work - a force moving an object through a distance
  • Electrical work - charges moving due to a potential difference
  • Heating - due to temperature difference caused electrically or by chemical reaction
  • Radiation - energy transferred as a wave, eg light and infrared
• Doing 'work'


  The scientific way of saying that energy has been transferred
• Transfer diagrams


  • The boxes show the energy stores and the arrows show the energy transfers
• Sankey diagrams


  • Start off as one arrow that splits into two or more points, showing how all of the energy in a system is transferred into different stores. The width of the arrow is drawn to scale to show the amount of energy
• Sankey diagrams are really useful when the amount of energy in each of the energy sources is known
• Dissipation


  Often used to describe ways in which energy is wasted. Any energy that is not transferred to useful energy stores is said to be wasted because it is lost to the surroundings.
• In a mechanical system, energy is dissipated when two surfaces rub together. Work is done against friction
• Adding lubricant between the surfaces reduces this friction and so less heat is wasted.
• In an electrical context, new types of components can be more energy-efficient.
• Energy is usually lost by heating up the surroundings though sometimes energy is dissipated as sound waves.

  The ways in which energy is dissipated depends on the system:

  • for a radio or set of speakers, the electrical work is transferred into useful sound waves and infrared radiation is dissipated - ie wasted as heat energy
  • for a tumble dryer, the electrical work is transferred into useful internal (thermal) energy which helps to dry clothes - energy is dissipated by sound waves
• Energy can be transferred usefully, stored or dissipated, but it cannot be created or destroyed.