The conservation of energy

Energy cannot be created or destroyed, so it is always conserved. This means that energy is regularly transferred from one store to another, although sometimes it is considered to be 'wasted' when it is transferred to a store that is not useful.

Since energy is always conserved, all the energy in the universe was present at the Big Bang and will still be around at the very end of time.

Examples of conservation of energy

The skydiver

When a skydiver jumps out of a plane, the following energy transfers take place:

  • the skydiver's gravitational potential energy decreases as their altitude decreases
  • the skydiver's kinetic energy store increases as their speed increases
  • the thermal store of the air and the skydiver increases, as there is friction between the skydiver and the air particles
Energy transfer diagram, gravitational potential to kinetic and internal energy

No energy is destroyed or created during this process. As the gravitational store of energy decreases, the thermal and kinetic stores increase.

Smartphones

All smartphones contain a battery that acts as a chemical energy store. When a smartphone is in use, the following energy transfers take place:

  • the battery's chemical energy store is transferred by the flow of an electric current to light up the screen and to produce sound
  • the light that comes from a smartphone is emitted as visible radiation
  • sound waves are produced by a speaker that vibrates
  • chemical energy from the battery is also transferred into thermal energy (which is why phones heat up in use)
Energy transfer diagram of a smartphone