Wedge (mechanics)

# Wedge (mechanics)

Discussion

Encyclopedia
A wedge is a triangular
Triangle
A triangle is one of the basic shapes of geometry: a polygon with three corners or vertices and three sides or edges which are line segments. A triangle with vertices A, B, and C is denoted ....

shaped round tool
, a compound and portable inclined plane
Inclined plane
The inclined plane is one of the original six simple machines; as the name suggests, it is a flat surface whose endpoints are at different heights. By moving an object up an inclined plane rather than completely vertical, the amount of force required is reduced, at the expense of increasing the...

, and one of the six classical simple machine
Simple machine
A simple machine is a mechanical device that changes the direction or magnitude of a force.In general, they can be defined as the simplest mechanisms that use mechanical advantage to multiply force. A simple machine uses a single applied force to do work against a single load force...

s. 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
Force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...

applied to its blunt end into forces perpendicular (normal
Surface normal
A surface normal, or simply normal, to a flat surface is a vector that is perpendicular to that surface. A normal to a non-flat surface at a point P on the surface is a vector perpendicular to the tangent plane to that surface at P. The word "normal" is also used as an adjective: a line normal to a...

) to its inclined surfaces. The mechanical advantage
Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device or machine system. Ideally, the device preserves the input power and simply trades off forces against movement to obtain a desired amplification in the output force...

of a wedge is given by the ratio of the length of its slope to its width. 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.

## History

Perhaps the first example of a wedge is the hand axe, also see biface
Biface
In archaeology, a biface is a two-sided stone tool and is used as a multi purposes knife, manufactured through a process of lithic reduction, that displays flake scars on both sides. A profile view of the final product tends to exhibit a lenticular shape...

and Olorgesailie
Olorgesailie
Olorgesailie is a geological formation in East Africa containing a group of Lower Paleolithic archaeological sites. It is on the floor of the Eastern Rift Valley in southern Kenya, southwest of Nairobi along the road to Lake Magadi. Olorgesailie is noted for the large number of Acheulean hand...

. A hand axe is made by chipping stone, generally flint, to form a bifacial edge, or wedge. A wedge is a simple machine that transforms lateral force and movement of the tool into a transverse splitting force and movement of the workpiece. The available power is limited by the effort of the person using the tool, but because power is the product of force and movement, the wedge amplifies the force by reducing the movement. This amplification, or mechanical advantage
Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device or machine system. Ideally, the device preserves the input power and simply trades off forces against movement to obtain a desired amplification in the output force...

is the ratio of the input speed to output speed. For a wedge this is given by 1/tanα, where α is the tip angle. The faces of a wedge are modeled as straight lines to form a sliding or prismatic joint
Prismatic joint
A prismatic joint provides a linear sliding movement between two bodies, and is often called a slider, as in the slider-crank linkage. A prismatic joint is formed with a polygonal cross-section to resist rotation...

.

The origin of the wedge is unknown likely because it has been in use for over 9000 years. In ancient Egypt
Ancient Egypt
Ancient Egypt was an ancient civilization of Northeastern Africa, concentrated along the lower reaches of the Nile River in what is now the modern country of Egypt. Egyptian civilization coalesced around 3150 BC with the political unification of Upper and Lower Egypt under the first pharaoh...

ian quarries
Quarry
A quarry is a type of open-pit mine from which rock or minerals are extracted. Quarries are generally used for extracting building materials, such as dimension stone, construction aggregate, riprap, sand, and gravel. They are often collocated with concrete and asphalt plants due to the requirement...

, bronze
Bronze
Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive. It is hard and brittle, and it was particularly significant in antiquity, so much so that the Bronze Age was named after the metal...

wedges were used to break away blocks of stone used in construction. Wood
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...

en wedges, that swelled after being saturated with water, were also used. Some indigenous peoples of the Americas
Indigenous peoples of the Americas
The indigenous peoples of the Americas are the pre-Columbian inhabitants of North and South America, their descendants and other ethnic groups who are identified with those peoples. Indigenous peoples are known in Canada as Aboriginal peoples, and in the United States as Native Americans...

used antler
Antler
Antlers are the usually large, branching bony appendages on the heads of most deer species.-Etymology:Antler originally meant the lowest tine, the "brow tine"...

wedges for splitting and working wood to make canoes, dwellings and other objects.

## Use of a wedge for lifting and separating

Wedges are be used to lift heavy objects, separating them from the surface upon which they rest.

Consider a block that is to be lifted by a wedge. As the wedge slides under the block, the block slides up the sloped side of a wedge. This lifts the weight FB of the block. The horizontal force FA needed to lift the block is obtained by considering the velocity of the wedge vA and the velocity of the block vB. If we assume the wedge does not dissipate or store energy, then the power into the wedge equals the power out, so
or
The velocity of the block is related to the velocity of the wedge by the slope of the side of the wedge. If the angle of the wedge is α then
which means
Thus, the smaller the angle α the greater the ratio of the lifting force to the applied force on the wedge. This is the mechanical advantage
Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device or machine system. Ideally, the device preserves the input power and simply trades off forces against movement to obtain a desired amplification in the output force...

of the wedge. This formula for mechanical advantage applies to cutting edges and splitting operations as well as to lifting.

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
Taper
In cymbal making, taper refers to the gradual change in thickness from the bell to the rim of the cymbal. It is one of the key features that determines the tone of the cymbal....

used to finely adjust the distance between objects is called a shim, and is commonly used in carpentry.

The tips of forks and nails
Nail (engineering)
In woodworking and construction, a nail is a pin-shaped, sharp object of hard metal or alloy used as a fastener. Formerly wrought iron, today's nails are typically made of steel, often dipped or coated to prevent corrosion in harsh conditions or improve adhesion...

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
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...

parts (poppet valve
Poppet valve
A poppet valve is a valve consisting of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem. The shaft guides the plug portion by sliding through a valve guide...

s), bicycle
Bicycle
A bicycle, also known as a bike, pushbike or cycle, is a human-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist, or bicyclist....

parts (stem
Stem (bicycle part)
The stem is the component on a bicycle that connects the handlebars to the steerer tube of the bicycle fork. Sometimes called a goose neck, a stem's design belongs to either a quill or threadless system, and each system is compatible with respective headset and fork designs:-Quill vs...

s and eccentric
Eccentric (mechanism)
In mechanical engineering, an eccentric is a circular disk solidly fixed to a rotating axle with its centre offset from that of the axle ....

bottom bracket
Bottom bracket
The bottom bracket on a bicycle connects the crankset to the bicycle and allows the crankset to rotate freely. It contains a spindle that the crankset attaches to, and the bearings that allow the spindle and cranks to rotate. The chainrings and pedals attach to the cranks...

s), and door
Door
A door is a movable structure used to open and close off an entrance, typically consisting of a panel that swings on hinges or that slides or rotates inside of a space....

s.

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).

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

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.

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.

• Axe
Axe
The axe, or ax, is an implement that has been used for millennia to shape, split and cut wood; to harvest timber; as a weapon; and as a ceremonial or heraldic symbol...

A blade is that portion of a tool, weapon, or machine with a cutting edge and/or a pointed tip that is designed to cut and/or puncture, stab, slash, chop, slice, thrust, or scrape animate or inanimate surfaces or materials...

• Knife
Knife
A knife is a cutting tool with an exposed cutting edge or blade, hand-held or otherwise, with or without a handle. Knives were used at least two-and-a-half million years ago, as evidenced by the Oldowan tools...

• Log splitter
Log splitter
A log splitter is a piece of machinery or equipment used for splitting firewood from softwood or hardwood logs that have been pre-cut into sections , usually by chainsaw or on a saw bench. Many log splitters consist of a hydraulic or electrical rod and piston assembly and these are often rated by...

• Plug and feather
Plug and feather
Plug and feather, also known as plugs and wedges, feather and wedges, wedges and shims, pins and feathers and feather and tare refers to a technique and a three-piece tool set used to split stone.-Description:...

• Pushpin
• Splitting maul
• Scalpel
Scalpel
A scalpel, or lancet, is a small and extremely sharp bladed instrument used for surgery, anatomical dissection, and various arts and crafts . Scalpels may be single-use disposable or re-usable. Re-usable scalpels can have attached, resharpenable blades or, more commonly, non-attached, replaceable...

• Screw
Screw
A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...