Hey guys, I am trying to conceptualize as to why shear stress in a vessel is highest at the wall of the vessel and why it is at a minimum at the center. First let me see if I actually understand shear stress - In a vessel with blood flow, it is the force required to overcome the viscosity that causes blood to flow at different rates. Now, velocity of the blood (fluid) is highest at the center and lowest (~0) at the wall. I just don't understand why there is a difference b/w the center and the periphery. The way I understood it, there was a more or less gradual decrease in the velocity of blood as it reached the wall. As such, the shear stress would be more or less be equal at the wall and the center. I know I'm not understanding something. Thanks for the help. Much appreciated.