text: By definition, shear flow through a cross section of thickness t is calculated using , where . Thus the equation for shear flow at a particular depth in a particular cross-section of a thin-walled structure that is symmetric across its width is
  where
  :q - the shear flow
  :V - the shear force perpendicular to the neutral axis x at the cross-section of interest
  :Q - the first moment of area (aka statical moment) about the neutral axis x for the cross section of the structure above the depth in question
  :I - the second moment of area (aka moment of inertia) about the neutral axis x for the structure (a function only of the shape of the structure)