A washing machine (laundry machine, clothes washer, or washer) is a home appliance used to wash laundry. The term is mostly applied to machines that use water as opposed to dry cleaning (which uses alternative cleaning fluids, and is performed by specialist businesses) or ultrasonic cleaners. The user adds laundry detergent, which is sold in liquid or powder form, to the wash water.
Clothes washer technology developed as a way to reduce the manual labor spent, providing an open basin or sealed container with paddles or fingers to automatically agitate the clothing. The earliest machines were hand-operated and constructed from wood, while later machines made of metal permitted a fire to burn below the washtub, keeping the water warm throughout the day’s washing. There are mechanical washing machines dating from the 17th century.
Many front-loading machines have internal electrical heating elements to heat the wash water, to near boiling if desired. The rate of chemical cleaning action of the detergent and other laundry chemicals increases greatly with temperature, in accordance with the Arrhenius equation. Washing machines with internal heaters can use special detergents formulated to release different chemical ingredients at different temperatures, allowing different types of stains and soils to be cleaned from the clothes as the wash water is heated up by the electrical heater.