# Time of Impact of Gas Molecules on the Inner Wall of a Pressure Vessel

Zahid Iftikhar
In derivation of relation for pressure of Gas ,(see pic below) the time for rate of change of momentum of molecules should be the time for which the wall of the vessel and the molecules kept interacting with each other, not the time between successive collisions. As circumscribed below, my confusion is how the time between two such collisions can be equal to the time of impact between the wall and the molecules. The time of impact has actually caused the change of momentum, thereby causing the pressure. I further argue, that let us suppose there are 100 or so molecules colliding just once on the wall, bounce back, and then never return (just assume), during this one-time collision, pressure has been exerted on the wall of the vessel. In this case, there is no time between successive collisions involved. I would be obliged if learned people on this forum help me to understand. High regards
Zahid