All of the radiation that passes through a circle of radius rand area Ar=π2,perpendicular to the direction of propagation, is absorbed by the particle, so the force of the radiation on the particle has magnitude FpAPrRcPrrr===ππ222244. The force is radially outward from the Sun. Notice that both the force of gravity and the force of the radiation are inversely proportional to R2. If one of these forces is larger than the other at some distance from the Sun, then that force is larger at all distances. The two forces depend on the particle radius rdifferently: Fgis proportional to r3and Fris proportional to r2. We expect a small radius particle to be blown away by the radiation pressure and a large radius particle with the same density to be pulled inward toward the Sun. The critical value for the radius is the value for which the two forces are equal. Equating the expressions for
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This note was uploaded on 06/03/2011 for the course PHY 2049 taught by Professor Any during the Spring '08 term at University of Florida.