Inclined plane is one of six simple machines. Its various forms can be found in nature. Man started to use it deliberately to lift heavy burdens while constructing great buildings. The theory of inclined plane is useful in the construction of ski-jumps and cable railways. The inclined plane can be used for measuring acceleration due to gravity or for measuring the coefficient of dragging and rolling friction. On the inclined plane, a simple decomposition of gravity force can be demonstrated and complex motion theory can be studied as well.