Which term describes an applied force causing an opposite, parallel sliding motion between planes, as defined in biomechanics?

• A. Tension
• B. Friction
• C. Shear
• D. Compression

Answer: (C)

Shear is the force that causes opposite, parallel sliding between adjacent planes. When a force acts parallel to a surface, it tends to slide one layer over another, producing motion in opposite directions across the plane. This is different from tension, which pulls tissues along their length to stretch them; and compression, which pushes tissues toward one another. Friction is the resisting force that opposes this sliding, not the force that causes the sliding itself. In biomechanics, shear stresses occur at interfaces like cartilage surfaces or where soft tissues slide past each other during movement, helping explain how tissues can be damaged when sliding occurs between layers.