  Polymers in confined spaces lose conformational entropy. This induces a net
repulsive entropic force on the walls of the confining space. A model for this
phenomenon is a lattice walk between confining walls, and in this paper a model
of an adsorbing partially directed walk is used. The walk is placed in a half
square lattice $L^2_+$ with boundary $\partial L^2_+$, and confined between two
vertical parallel walls, which are vertical lines in the lattice, a distance
$w$ apart. The free energy of the walk is determined, as a function of $w$, for
walks with endpoints in the confining walls and adsorbing in $\partial L^2_+$.
This gives the entropic force on the confining walls as a function of $w$. It
is shown that there are zero force points in this model and the locations of
these points are determined, in some cases exactly, and in other cases
asymptotically.
