An inclined plane is a ramp that reduces the force necessary to overcome the force of gravity when changing the elevation of mass in a gravitational field.
By changing the angle of the ramp one can usefully vary the force necessary to raise or lower a load. For example:
A wagon trail on a steep hill will often traverse back and forth to reduce the gradient experienced by a team pulling a heavily loaded wagon. This same techique is used today in modern freeways which travel through steep mountain passes. Some steep passes have separate truck routes that reduce the grade by winding along a separate path to rejoin the main route after a particularly steep section is past while smaller automobiles take the straighter steeper route with a resulting savings in time.
Another modern example is a long wheelchair access ramp which makes it easier to access alternate elevations by extending the distance traveled horizontally (run) to achieve the desired elevation change (rise).
It is important in the history of science, engineering and technology for a variety of reasons:
The ramp or inclined plane was useful in building early stone edifices, in roads and aquaducts, and military assault of fortified positions.
Experiments with inclined planes helped early physicists such as Galileo Galilei quantify the behavior of nature with respect to gravity, mass, acceleration, etc.
Detailed understanding of inclined planes and their use helped lead to the understanding of how vector quantities such as forces can be usefully decomposed and manipulated mathematically. This concept of superposition and decomposition is critical in many modern fields of science, engineering, and technology.
The term inclined plane is also used for a funicular.
An inclined plane is also a name for a system used on some canals for raising boats between different water levels. Typically a canal inclined plane consists of a diagonal slope on which there are railss, and boats are raised between different levels by sailing into watertight "bathtub" type containers which have watertight doors at each end. These containers are then drawn up or down hill on the rails, by means of a stationary engine. When the container has reached the top or bottom of the slope, the end of the container is opened and the boat sails out. Examples of these can be found on a number of canals around the world.