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A 'wedge' is a portable double inclined plane, used to separate two objects, or portions of objects, through the application of force, perpendicular to the inclined surfaces, developed by conversion of force applied to the wide end. The mechanical advantage of a wedge depends on the ratio of its length to its thickness.
Where a short wedge with a wide angle does the job faster, it requires more force than a long wedge with a smaller angle.
The origin of the wedge is unknown, because it has been in use as early as the Stone Age. Circa 3000 BC, in Ancient Egypt quarrys, bronze wedges were used to break away blocks of rock used for construction. Wood wedges, that swelled after being wet, were also used.
Examples include axes, nails and teeth. Knives, scissors, and chisels can sometimes be used as wedges, however, they are more fundamentally cutting implements. A door stop (door wedge) can also be regarded as wedge, but its main function is to provide a friction between the door and the ground rather than to separate materials: nevertheless the friction generates a force which prevents the door from moving.
A fork or nail can also be considered a type of wedge. While a nail would slice into wood when hammered, a bolt would not be pushed in. This is because a nail is a wedge and a bolt is not. A nail is tapered to a point at its end, then gets thicker farther up towards the head of the nail.
Wedges can also be used to lock engine parts in place, e.g. see poppet valve.

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Mechanical advantage

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Mechanical advantage

To find the mechanical advantage of a wedge, take the length of the slope of the wedge and divide it by the length of the thick part of the wedge. Therefore the formula for a wedge is:
$MA=\{S\; over\; T\}$
The thinner the angle of the wedge, the more mechanical advantage it will have.
Despite this, one reason that many wedges have a wide angle is that an elastic material, such as wood, will bind a narrow wedge more readily than a wide wedge. This is why splitting mauls have a much larger angle than an axe.

External links

★ (Mechanics of) wedges and screws