1. The problem statement, all variables and given/known data to resist the bending, there must be reaction force(blue) act against the applied force(red), the reaction force that resist bending is the longitidunal normal force , right? why the author stated it as longitidunal shear force, is it wrong? 2. Relevant equations 3. The attempt at a solution longitidunal shear force is the green colour arrow, right? how could the force resist the bending?