The interactions between multi-bodies (particles) will be investigated when the interstitial fluid is at a such low pressure that the continuity equation does not hold. Analytical solutions to the gas kinetic equations ware proposed to describe the interaction of two spheres by considering the entire range of the Knudsen number. Molecular dynamics methods, including the time correlation formalism and generalized Brownian dynamics, are used for more complex systems of particles moving in gases. The work has relevance to aerosol science and technology.
