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Shear force

Coplanar forces acting on the same body in opposite directions / From Wikipedia, the free encyclopedia

In solid mechanics, shearing forces are unaligned forces acting on one part of a body in a specific direction, and another part of the body in the opposite direction. When the forces are collinear (aligned with each other), they are called tension forces and compression forces. William A. Nash defines shear force in terms of planes: "If a plane is passed through a body, a force acting along this plane is called a shear force or shearing force."[1]

Shearing forces act in one direction at the top, and the opposite direction at the bottom, causing shearing deformation.
A crack or tear may develop in a body from parallel shearing forces acting in opposite directions at different points of the body. If the forces were aligned with each other, they would elongate or shorten the body, depending on their direction, rather than tear or crack it.