Gravity feed is the use of

earth's gravity The gravity of Earth, denoted by , is the net acceleration that is imparted to objects due to the combined effect of gravitation (from mass distribution within Earth) and the centrifugal force (from the Earth's rotation). It is a vector quantit ...

to move something (usually a

liquid A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, an ...

) from one place to another. It is a simple means of moving a liquid without the use of a

pump A pump is a device that moves fluids ( liquids or gases), or sometimes slurries, by mechanical action, typically converted from electrical energy into hydraulic energy. Pumps can be classified into three major groups according to the method the ...

. A common application is the supply of fuel to an

internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal co ...

by placing the fuel tank above the engine, e.g. in

motorcycle A motorcycle (motorbike, bike, or trike (if three-wheeled)) is a two or three-wheeled motor vehicle steered by a handlebar. Motorcycle design varies greatly to suit a range of different purposes: long-distance travel, commuting, cruisin ...

lawn mower A lawn mower (also known as a mower, grass cutter or lawnmower) is a device utilizing one or more revolving blades (or a reel) to cut a grass surface to an even height. The height of the cut grass may be fixed by the design of the mower, but g ...

s, etc. A non-liquid application is the carton flow shelving system. Ancient

Roman aqueduct The Romans constructed aqueducts throughout their Republic and later Empire, to bring water from outside sources into cities and towns. Aqueduct water supplied public baths, latrines, fountains, and private households; it also supported min ...

s were gravity-fed, as water supply systems to remote villages in developing countries often are. In this case the flow of water to the village is provided by the

hydraulic head Hydraulic head or piezometric head is a specific measurement of liquid pressure above a vertical datum., 410 pages. See pp. 43–44., 650 pages. See p. 22. It is usually measured as a liquid surface elevation, expressed in units of length, ...

, the vertical distance from the intake at the source to the outflow in the village, on which gravity acts; while it is opposed by the friction in the pipe which is determined primarily by the length and diameter of the pipe as well as by its age and the material of which it is made.

See also