Poiseuille's law describes the velocities of fluids flowing in a tube—for example, the flow of blood in a vein. This law applies when the velocities are not too large—more specifically, when the flow has no turbulence. In this case the flow is

*laminar*, which means that the paths of the flow are all parallel to the tube walls. The law states that

, where

*v* is the velocity,

*k* is a constant (which depends on the fluid, the tube, and the units used for measurement),

*R* is the radius of the tube, and

*r* is the distance from the centerline of the tube. Since

*k* and

*R* are fixed for any application,

*v* is a function of

*r* alone, and the formula gives the velocity at a point of distance

*r* from the centerline of the tube

(a) What is

*r* for a point along the walls of the tube?

(In so many words, this basicly means to get r by itself, right?)

(b) What is the velocity of the fluid along the walls of the tube?

(...Wait, it didn't give me a value? I'm going to take a wild guess and say the fluid along the wall is zero.)