This lecture covers the derivation of collision flux using the distribution of velocity components orthogonal to a surface. It simplifies the Maxwell-Boltzmann distribution for molecules striking a surface. The instructor explains how the rate of molecule impingement depends on the velocity component distribution. The lecture also discusses the Knudsen method for measuring vapor pressure by effusion, including the loss of mass through a small hole. Various collision densities and collision flux calculations are explored, emphasizing the importance of velocity component distribution. The content delves into the relationship between collision flux, Maxwell-Boltzmann distribution, and the rate of molecule impingement.