The conservation of energy

Energy can be transferred usefully, stored or dissipated, but it cannot be created or destroyed.

In all cases, energy comes from one store and is transferred to another store. This means that 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, he begins to lose gravitational potential energy as his height decreases and he gains kinetic energy as his speed increases.

Energy transfer diagram, gravitional potential to kinetic and internal energy

However, not all of the gravitational potential energy is transferred into kinetic energy as some work is done pushing against the air particles. Some of the gravitational potential energy is transferred to the air particles and is stored as internal energy.

Smartphones

All smartphones contain a battery that stores chemical energy. When a smartphone is in use, electrical work is done and a current flows - the battery’s chemical energy is transferred in a number of ways to light the screen and produce sound.

The light that comes from a smartphone is emitted as light radiation, and the sound waves are produced by a speaker that vibrates back and forth.

In addition to this, many smartphones also heat up when used, so chemical energy is also transferred into internal energy. This energy is stored in the atoms of the smartphone’s conductors and it is these atoms that emit infrared radiation.

Energy transfer diagram of a smartphone