text: Consider an infinitely long plate which is suddenly made to move with constant velocity  in the  direction, which is located at  in an infinite domain of fluid, which is at rest initially everywhere. The incompressible Navier-Stokes equations reduce to
  where  is the kinematic viscosity. The initial and the no-slip condition on the wall are
  the last condition is due to the fact that the motion at  is not felt at infinity. The flow is only due to the motion of the plate, there is no imposed pressure gradient.