  Lubrication expressions for the friction coefficients of a spherical particle
moving in a fluid between and along two parallel solid walls are explicitly
evaluated in the low-Reynolds-number regime. They are used to determine
lubrication expression for the particle free motion under an ambient Poiseuille
flow. The range of validity and the accuracy of the lubrication approximation
is determined by comparing with the corresponding results of the accurate
multipole procedure. The results are applicable for thin, wide and long
microchannels, or quasi-two-dimensional systems.
