In mechanics, which property is defined as the force per unit area acting parallel to a surface element?

• A. Elastic limit
• B. Shear stress
• C. Torsion
• D. Capacitance

Answer: (B)

Shear stress is the force per unit area acting parallel to a surface element. In mechanics, the internal traction on an imaginary plane within a material has a tangential (parallel) component and a normal (perpendicular) component. The tangential component per unit area is the shear stress, expressed as the parallel force divided by the plane’s area. This describes how layers slide relative to each other under load. For intuition, picture sliding the top layer of a stack of cards over the bottom layer—the parallel force over the contact area creates shear stress. The other terms aren’t definitions of this quantity: the elastic limit is about yield, torsion is twisting that can cause shear stresses but isn’t the defining measure, and capacitance is an electrical property.