The velocity distribution function associated with a molecule entering a dilute gas, either in equilibrium or with a temperature gradient, is evaluated by solving a forward Boltzmann equation.In the equilibrium case, the velocity distribution function associated with the molecules, other than the incoming molecule, is also evaluated and the contributions to the Kubohyphen;type coefficient of thermal conduction from both distribution functions are evaluated for Maxwellian molecules. These contributions give the coefficient of thermal conduction obtained by the Chapmanmdash;Enskog method.The various mean accelerations experienced by a molecule moving in a gas are calculated using the above solutions of the forward equation and also the solutions of a backward Boltzmann equation. These expressions are then used to evaluate the friction coefficients, first introduced by Kirkwood, for both equilibrium and nonequilibrium gases.An experimental procedure using radioactive particles injected into a gas is also suggested as a method of confirming the obtained results.
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