Wedge (mechanical device)

A wood splitting wedge

A wedge is a triangular shaped tool, a compound and portable inclined plane, and one of the six classical simple machines. It can be used to separate two objects or portions of an object, lift an object, or hold an object in place. It functions by converting a force applied to its blunt end into forces perpendicular (normal) to its inclined surfaces.[1] The mechanical advantage of a wedge is given by the ratio of the length of its slope to its width.[2][3] Although a short wedge with a wide angle may do a job faster, it requires more force than a long wedge with a narrow angle.

Contents

History

The origin of the wedge is unknown likely because it has been in use for over 9000 years. In ancient Egyptian quarries, bronze wedges were used to break away blocks of stone used in construction. Wooden wedges, that swelled after being saturated with water, were also used. Some indigenous peoples of the Americas used antler wedges for splitting and working wood to make canoes, dwellings and other objects.

Examples for lifting and separating

Wedges can be used to lift heavy objects, separating them from the surface they rest on. They can also be used to separate objects, such as blocks of cut stone. Splitting mauls and splitting wedges are used to split wood along the grain. A narrow wedge with a relatively long taper used to finely adjust the distance between objects is called a shim, and is commonly used in carpentry.

The tips of forks and nails are also wedges, as they split and separate the material into which they are pushed or driven; the shafts may then hold fast due to friction.

Examples for holding fast

Wedges can also be used to hold objects in place, such as engine parts (poppet valves), bicycle parts (stems and eccentric bottom brackets), and doors.

A wedge-type door stop (door wedge) functions largely because of the friction generated between the bottom of the door and the wedge, and the wedge and the floor (or other surface).

Mechanical advantage

Cross-section of a splitting wedge with its length oriented vertically. A downward force produces forces perpendicular to its inclined surfaces.

The mechanical advantage of a wedge can be calculated by dividing the length of the slope by the wedge's width:[2]

MA={S \over W}

The more acute, or narrow, the angle of a wedge, the greater the ratio of the length of its slope to its width, and thus the more mechanical advantage it will yield.[3]

However, in an elastic material such as wood, friction may bind a narrow wedge more easily than a wide one. This is why the head of a splitting maul has a much wider angle than that of an axe.

See also

References

  1. ↑ Wedges and screws, http://em-ntserver.unl.edu/Negahban/em223/note16/note16.htm, retrieved 2009-07-29 .
  2. ↑ 2.0 2.1 Bowser, Edward Albert (1920), An elementary treatise on analytic mechanics: with numerous examples (25th ed.), D. Van Nostrand Company, pp. 202–203, http://books.google.com/?id=mE4GAQAAIAAJ .
  3. ↑ 3.0 3.1 McGraw-Hill Concise Encyclopedia of Science & Technology, Third Ed., Sybil P. Parker, ed., McGraw-Hill, Inc., 1992, p. 2041.
Simple machine
Classical simple machines
Inclined plane · Lever · Pulley · Screw · Wedge · Wheel and axle