Energy dissipation

No system is perfect. Whenever there is a change in a system, energy is transferred and some of that energy is dissipated.

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Dissipation is a term that is often used to describe ways in which energy is wasted. Energy that is not transferred to useful energy stores is said to be wasted, because it is usually lost to the surroundings.

Dissipation through thermal energy

In a mechanical system, such as a conveyor belt, energy is dissipated when two surfaces rub together. Work is done against friction, which causes heating of the two surfaces. The thermal energy store of the surfaces increases, so energy is dissipated rather than being usefully transferred. A lubricant between the surfaces reduces this friction, meaning less energy is wasted.

New electrical products tend to be more energy efficient than older designs. For example, LED light bulbs are more efficient than filament lamps because a larger proportion of the electrical energy store is transferred to the surroundings by light rather than by heating.

Dissipation through sound energy

In a tumble dryer, electrical work is transferred into useful thermal energy, which helps to dry clothes. However, energy is dissipated by vibrations, which we call sound waves. This is why tumble dryers can be very noisy.

Electrical generators are also very noisy. Some of the electric and magnetic energy store of the generator is dissipated by vibrations as the generator spins. We sense these vibrations as sound.