<P> Therefore the first moment of the cross section about its neutral axis must be zero . Therefore the neutral axis lies on the centroid of the cross section . </P> <P> Note that the neutral axis does not change in length when under bending . It may seem counterintuitive at first, but this is because there are no bending stresses in the neutral axis . However, there are shear stresses (τ) in the neutral axis, zero in the middle of the span but increasing towards the supports, as can be seen in this function (Jourawski's formula); </P> <Dl> <Dd> τ = T Q w I (\ displaystyle \ tau = (\ frac (TQ) (wI))) </Dd> </Dl> <Dd> τ = T Q w I (\ displaystyle \ tau = (\ frac (TQ) (wI))) </Dd>

Difference between center of gravity and neutral axis