Which description best defines shear force?

• A. A force acting perpendicular to the surface
• B. A force acting parallel to the surface
• C. A force causing compression
• D. A force around a joint axis

Answer: (B)

Shear force is the component of a force that acts parallel to a surface, trying to slide one layer of material over another. This is different from a force that acts perpendicular to the surface, which would push surfaces toward or away from each other (normal force). It’s also not about rotation around a joint axis—that would be a moment or torque. So describing a force that acts parallel to the surface captures the essence of shear force.