On the electrostatic potential and charge of cosmic grains. IV - Locally amplifiable force onset producing acceleration.

The force exerted on a spherical dust grain due to ejection of particles from the grain by photoemission is determined, and the dependence of the photoelectron emission on the various parameters involved is discussed. It is shown that, unlike radiation pressure, it does not depend only on the incident radiation and the absorption properties of the grain, but also on the characteristics of the ambient plasma. The photoemission can produce a dynamical effect which can be of the order of the radiation pressure or even dominate it. The ability of this effect to brake the grain motion is also addressed. The braking can be important in cases where the acceleration is counterbalanced by other forces like gravitation and inertia, for instance in the case of a grain gravitationally linked to a large body like a star.