  We demonstrate a technique for simultaneously measuring each component of the
force vectors and mobility tensor of a small collection of colloidal particles
based on observing a set of particle trajectories. For a few-body system of
micron-sized polymer beads in oil separated by several particle radii, we find
that the mobility tensor is well-described by a pairwise Stokeslet model. This
stands in contrast to the electrostatic interactions, which were found to
deviate significantly from a pairwise model. The measurement technique
presented here should be simple to extend to systems of heterogeneous,
non-spherical particles arranged in arbitrary 3D geometries.
