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 energy from the gravitational potential energy store as his height decreases, and his kinetic energy store increases as his speed increases.

Energy transfer diagram, gravitional potential to kinetic and internal energy

However, not all of the energy lost from the gravitational potential energy store is transferred into the kinetic energy store. 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, the battery's chemical energy store decreases. The energy is transferred via the electrical work pathway to light the screen and produce sound.

The light that comes from a smartphone is emitted via the light radiation pathway, and the sound waves are produced by a speaker that vibrates back and forth and are emitted via the sound radiation pathway. Eventually both the light and the sound pathways lead to (very small) increases in the internal energy store (temperature) of the surroundings.

In addition to this, many smartphones also heat up when used, so energy from the chemical store is also transferred to the internal energy store. This causes an increase in the temperature of the phone and causes it to emit more energy via the infrared radiation pathway.

Energy transfer diagram of a smartphone