The Traction Vector on a surface is computed as the product of the stress tensor and which quantity?

• A. Unit Normal Vector
• B. Displacement Vector
• C. Position Vector
• D. Velocity Vector

Answer: (A)

The traction on a surface is determined by the stress tensor acting on the surface’s orientation, which is captured by the surface normal. Specifically, the traction vector is obtained by multiplying the stress tensor by the unit normal to the surface: t = σ · n. The unit normal defines how the surface is oriented in space, and the stress tensor transforms that orientation into the force per unit area acting on the surface.

Displacement, position, or velocity vectors don’t describe the surface’s orientation; they describe movement or location, not how internal forces are transmitted across a boundary. That’s why the unit normal is the quantity that must be used to compute traction.