The elementary interaction forcefpfor a small normal conducting precipitate particle is usually estimated assuming that the entire condensation energy of the superconductor 1/2  &mgr;0H2cis lost in the volume of the particle, i.e., that the particle is equivalent to a void. It is demonstrated that this assumption, which neglects the proximity effect, leads to a serious over estimate offp, by as much as three orders of magnitude. The ratio offpof a normal precipitate tofpof a void of the same volume is shown to be of the order (t/&xgr;0)2, wheretis the smallest dimension of the particle and &xgr;0is the BCS coherence length. In addition, the ratio is temperature dependent, becoming smaller (larger correction) asTapproachesTc. These predictions are compared with recent experimental measurements of pinning by voids and precipitates and are shown to rationalize some hitherto puzzling experimental discrepancies between pinning by the two types of defects. Application of these ideas to flux pinning by other defects, such as grain boundaries and dislocations, is also discussed.