This is not a homework question! I am observing that a thin, flat disk made from a material whose density is gradually increasing, shrinks in the radial direction (of course) but appears to grow very slightly in the z-direction. The change in density is supposed to be isotropic. Is growth in the z-direction predicted or an artifact of my experiment? I don't know enough continuum mechanics to solve this problem or even how to search for a solution. Is the solution to this problem somewhere in the literature?