Ok....this is a thought model to help me understand some things you have a cylinder with a gas in it. You also have moveable piston. I move the piston into the cylinder, compressing the gas by 25% of the original volume. I know the pressure of the gas will increase for two reasons: Decreased volume (increased density) I have done work on the gas, transfering energy to the gas, which appears as an increase in gas temperature , which also increases the pressure along with the increased density (decreased volume) I know because of the random motion of the molecules (Vx, Vy, and Vz) the pressure will increase equally in all directions THE QUESTION: When I moved the piston into the cylinder, I know that I did work on the gas, increasing the temperature, but the "molecules" that were in contact with the piston when I moved the piston, don't they have a "momentum" imparted to them also in the down "-Y" direction. Wouldn't this momentum eventually reach the bottom of the cylinder (through transfers), and cause some type of small pressure fluctuation. Doesn't gas pressure have some kind of statistical element to it? Would this "flow of momentum" sway the statistical average for a very short (extremely short) period of time?