Wedges

A wedge is a machine that is useful for adjusting the elevation of structural or mechanical parts, providing stability for heavy objects, and splitting a body into two parts.

Consider using a wedge to lift a heavy slab.

The wedge amplifies the applied force into much larger force directed almost perpendicular to the applied force.

There are seven unknowns, including the applied force for the motion of the wedge and six normal and frictional forces.

They can be determined using four force equilibrium equations applied to the wedge and the slab and three frictional equations applied at each contact surface.

To lower the slab, the frictional forces act in the opposite sense.

Provided the coefficient of friction is very small or the wedge angle is large, the applied force must act to the right to hold the slab.

If the applied force is removed and friction forces hold the block, the wedge is considered self-locking. This condition is valid only when the wedge angle is less than twice the angle made by the reaction forces.