My question is about the energy exchange between gas particles and the walls of their container... If you consider a collection of gas molecules enclosed in a container, if the whole system is cooled (ie. like a balloon dipped in liquid nitrogen) as the gas particles collide with the inner wall of the enclosure they lose kinetic energy & therefore velocity, Thus the gas is cooled... My question is, do the gas particles only lose velocity in a vector direction perpendicular to the wall?? Or is the velocity lost in the direction of the particle's movement???? In other words, if you think of a box enclosure, and a molecule hits the wall at 30 degrees to perpendicular, would the velocity lost be directly in that direction or would it be lost solely in the perpendicular component??