1. The problem statement, all variables and given/known data in the formula of shear stress τ = (V)(Q) / It , Q=Ay = first moment of inertia of area, the area can be located above(or bottom) at the point of interest) when the chosen point is at the wall(boundary) , why shear stress = 0? 2. Relevant equations 3. The attempt at a solution When i choose area above the point of interest, there's nothing above A, so i understand that Q=0, shear stress = 0 But, when I choose the area below the point of interest, it's the whole coloured part, right? how can Q= 0 ?