A knife makes it easier to peel an apple, and an axe makes it easier to chop wood. A cheese grater cuts many pieces of cheese at the same time. These are all simple machines that make work easier. They are also all examples of a wedge. Wedges are another type of inclined plane.

Most machines that make use of inclined planes use them in the form of wedges. A wedge is really nothing more than a moving inclined plane, or two inclined planes back to back. Instead of having an object move up an inclined plane, the plane itself moves.

A wedge can be used to move things apart or to separate or cut something, such as a wedged knife is used to peel an apple. Most machines that cut use a wedge to do the cutting. A blade in the shape of a wedge converts a forward or downward movement into a parting movement at right angles to the blade. The axe is a wedge that changes the downward force into a powerful sideways force - which splits open a piece of wood. A nail hammered into a piece of wood is also a wedge that changes a strong downward force into a strong sideways force, which opens the wood to allow the nail to penetrate.