Vertical GRFs are directed how relative to the supporting surface?

Vertical GRFs are directed how relative to the supporting surface?

• A. Parallel
• B. Diagonal only
• C. Medial-lateral only
• D. Perpendicular

Answer: (D)

Vertical ground reaction forces reflect the component of the ground reaction that acts perpendicular to the contact surface. When the body presses against the surface, the ground pushes back with a normal force directed straight away from the surface; this is the vertical GRF. Friction can add forces along the surface, but the vertical GRF itself is perpendicular to the surface. So, its direction is perpendicular to the supporting surface.

Vertical ground reaction forces reflect the component of the ground reaction that acts perpendicular to the contact surface. When the body presses against the surface, the ground pushes back with a normal force directed straight away from the surface; this is the vertical GRF. Friction can add forces along the surface, but the vertical GRF itself is perpendicular to the surface. So, its direction is perpendicular to the supporting surface.