  Photophoretic motion can transport illuminated particles in protoplanetary
disks. In a previous paper we focused on the modeling of steady state
photophoretic forces based on the compositions derived from tomography and heat
transfer. Here, we present microgravity experiments which deviate significantly
from the steady state calculations of the first paper. The experiments on
average show a significantly smaller force than predicted with a large
variation in absolute photophoretic force and in the direction of motion with
respect to the illumination. Time-dependent modeling of photophoretic forces
for heat-up and rotation show that the variations in strength and direction
observed can be well explained by the particle reorientation in the limited
experiment time of a drop tower experiment. In protoplanetary disks, random
rotation subsides due to gas friction on short timescales and the results of
our earlier paper hold. Rotation has a significant influence in short duration
laboratory studies. Observing particle motion and rotation under the influence
of photophoresis can be considered as a basic laboratory analog experiment to
Yarkovsky and YORP effects.
