Waldmann's work on forces on small particles suspended in a nonhomogeneous monatomic gas is extended to a polyatomic gas of rotating molecules. Under the assumption that the coefficient of diffuse reflection is equal to 1, the force the gas exerts on a particle is calculated from an expansion of the distribution function. In general, this force consists of three contributions which are determined by the flow velocity, the translational heat flux, and the pressure tensor in the gas. The latter force vanishes for spheroidal particles, leaving only the frictional and the thermal force. These two forces are given for prolate and oblate spheroids. In particular, the dependence of the thermal force on the orientation of the particle's axis relative to the temperature gradient is discussed, and a comparison with the hydrodynamic and free molecular results is made.
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