What is the term for a force that acts in opposite directions across a material?

The term for a force that acts in opposite directions across a material is shear. Shear stress occurs when forces are applied parallel or tangent to a surface, leading to a sliding failure along a plane or layer within the material. This type of force effectively tries to make one part of the material slide over another, which is distinct from tension and compression that involve pulling and pushing along the material's length, respectively.

In practical applications, shear forces play crucial roles in structures, especially in beams that are subjected to transverse loads. Understanding shear is essential for ensuring that materials withstand these forces without experiencing shear failure, which can compromise structural integrity.