In physics, a wedge is a triangular-shaped tool and one of six classical simple machines. It is essentially a portable double-inclined plane used to either separate two objects, lift an object, or hold an object in place.
While it looks simple, the wedge is a master of force multiplication, converting a force applied to its blunt end into much larger forces acting perpendicular to its slanted faces.
How a Wedge Works
Fundamental principle of a wedge is direction of force. When you apply a downward force (input force) on wide end of the wedge, wedge then translates that energy into a sideways force (output force) against the object it is penetrating.
Force Geometry
Effectiveness of a wedge depends heavily on its shape:
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Thin Wedges: A long, thin wedge requires less input force to move through an object but must be driven a longer distance.
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Thick Wedges: A short, wide wedge requires a much larger input force but splits the object apart much faster.
Mechanical Advantage (MA)
The Mechanical Advantage of a wedge is a ratio that tells us how much machine multiplies our input force. For a wedge, this is calculated based on its physical dimensions:
Where:
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L is length of slanted face (or depth the wedge penetrates).
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t is thickness (width) of wide end.
Key Takeaway: The smaller angle of wedge, the higher mechanical advantage. This is why a sharp knife (a very thin wedge) cuts much more easily than a dull one.
Real-World Applications
Wedges are integrated into many tools we use daily. They generally fall into three functional categories:
| Function | Examples |
| Splitting/Cutting | Axes, knives, chisels, and even your front teeth (incisors). |
| Lifting | Shims used to level heavy furniture or stones. |
| Holding/Fastening | Doorstops, nails, and friction-based wedges in carpentry. |
Role of Friction
Unlike some other simple machines where friction is an enemy to efficiency, friction is often essential for a wedge.
For instance, when you hammer a nail (a pointed wedge) into wood, it is the friction between the wood fibers and the sides of the nail that keeps it from popping back out. Similarly, a doorstop relies entirely on friction to counteract the force of the door pushing against it.
Wedge vs. Inclined Plane
While they look similar, the primary difference is their movement:
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Inclined Plane: Remains stationary while object moves up slope (e.g., a wheelchair ramp).
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Wedge: The machine itself moves through or under object to do work.