The Boltzmann equation is used to obtain an expression for nu (E₀), the energy transferred to atomic motion by a fast atom of energy E₀ as it slows down in a host medium. The power law cross-section is used and, for small values of E₀/E_L, an exact power series solution in E₀/E_L may be written down. For large E₀/E_L it is necessary to make certain analytical approximations which result in accurate values for nu (E₀) over the complete energy range. Numerical values obtained from this formula agree well with the results of Lindhard and his co-workers (1963). The method based upon a solution obtained for the time-dependent radiation damage problem with electronic stopping.