Hello All, It is said that earth has an envelope of gases (air) surrounding it and that due to gravity the weight of this envelope of air exerts a force: on the surface of earth and any thing on it. The weight of air column on any surface divided by the area of the surface is always a constant quantity no matter what is the value of that area, and this very quantity is what we call the atmospheric pressure at that place. This seems quiet simple to understand. Things however complicate the matter (at least for me) when then the kinetic model of gas speaks of molecular collision (with the contact surface) as a reason for gas pressure.Imagine an open empty vessel (with air) at atmospheric pressure as per the kinetic model the molecules of the gas continue collide with the cylinder wall and thereby exerts pressure on the walls and every where inside the vessel. Now I sealed the vessel top keeping the inside pressure the same. The gas inside the vessel pushes the vessel walls outward trying to burst the vessel but as such the outer air also exert equal pressure to vessel walls inwards the vessel is thus neither collapsing nor bursting. But look what happen if this air filled sealed vessel is taken to a zero gravity space with no atmosphere? The two possible answers will be very different if one is answered thinking gravity(weight) and other molecular collisions as a cause of molecular collision. If gravity is zero the weight of air should be zero, so is the pressure inside the sealed vessel further remembering that no pressure is acting from out side in empty space the vessel thus due to zero weight of air in it; should have zero pressure in it and zero pressure out and will neither burst nor collapse. But according to kinetic model molecules should continue to collide (I thing independent of gravity) and due to collision with walls should exerts pressure to bursts the vessel. These two different answers posing a problem in understanding the real cause of atmospheric pressure. I mean if earth is considered not rotating(chances of escaping air is zero) and it suddenly lose gravity, than as per the weight of air column concept air pressure should be zero, while the fact that molecules in gas are always in random motion is at its place, and it doesn't justifies zero pressure in absence of gravity. I will be highly thankful if anybody explain what am i missing. With Regards, New Year Best Wishes!!