1) The document discusses momentum transfer through control volumes bounded by planes in a fluid flow system. It considers the x-direction momentum transfer through planes 1-2, 2-3, and 3-4. 2) By applying conservation of momentum, the rate of momentum transfer out of the control volume through plane 3-4 is shown to be equal to the sum of the transfers into the volume through planes 1-2 and 2-3. 3) The shear stress at the boundary is related to the velocity gradient outside the boundary layer, and is shown to approach zero with increasing distance from the leading edge.