Correct choice is (a) q^TT^e=2Π∫eu^TTrdl
The best I can explain: Traction, or tractive force, is the force used to generate motion between a body and a tangential surface, through the use of dry friction, though the use of shear force of the surface. Traction can also refer to the maximum tractive force between a body and a surface, as limited by available friction.