A washing machine is a machine designed to assist in the cleaning of clothing and other household fabric products such as towels and sheets. It is generally restricted to machines that use water as the primary cleaning solution, as distinct from dry cleaning which uses alternative cleaning fluids and is generally performed by specialist businesses in any case.
Mechanical washing machines have been available since at least the 19th century, and their basic principles of operation have remained largely unchanged. They first purpose is to suspend the material to be cleaned in water, which has had detergent added to it. The clothes and water are then "agitated" - moved back and forth in a chaotic manner. The water is then pumped out and the clothes partially dried by spinning them rapidly - a low-speed centrifuge. Clean water is then added and the clothes and water agitated to remove any remaining traces of the detergent. Finally, the clothes are (usually) spun again (though some clothes are removed immediately and dried by alternative means without further spinning).
Contemporary washing machines are available in two main configurations - "top loading" and "front loading". The "top loading" design, the most popular in the United States, places the clothes in a vertically-mounted cylinder with a propeller-like agitator in the center of the bottom of the cylinder. Clothes are loaded at the top of the machine, which is covered with a hinged door. The "front loading" design most popular in Europe instead mounts the cylinder horizontally, with loading through a glass door at the front of the machine. Agitation is supplied by the actual back-and-forth rotation of the cylinder.
Tests comparing front-loading and top-loading machines empirically have shown that, in general, front-loaders wash clothes more thoroughly, cause less wear, and use less water and energy than top-loaders. They also allow a dryer to be mounted directly above the washer, impossible with a top-loader. Top-loaders do have the advantages that they complete washing much faster, tend to cost less for the same capacity machine, and allow clothes to be removed at intermediate stages of the cycle (for instance, if some clothes within a wash are not to be spun.