Hey frndz, Can anyone explain me what is atmospheric pressure? How it acts? And is there any relation between Atmospheric pressure and Gravity........ What i have in my mind is that Atmospheric pressure is the Weight of gas in the atmosphere...so the pressure at any surface is the weight of air above that surface. In this case if a box open from one end is kept on flat surface in inverted position, then the pressure inside the box must be very very less as compare to atmospheric pressure. I think my understanding of pressure is wrong and i need to correct it. Please help.