Shear stress is defined as the force per unit area acting parallel to a surface element. Which option correctly states this?

• A. The force per unit area acting parallel to a surface.
• B. The force per unit area perpendicular to a surface.
• C. Energy stored due to deformation.
• D. The rate of rotation of an object.

Answer: (A)

The key idea is that shear stress measures how much tangential force acts on a surface per its area. It is the component of force parallel to the surface divided by the surface area, often written as tau = F_parallel / A. This is exactly what the statement says: the force per unit area acting parallel to a surface. The other options describe different concepts: force per area perpendicular to the surface is normal stress, energy stored due to deformation is strain energy, and rate of rotation is unrelated to stress.