I'm going to steal a picture that was used in a different thread in this forum. (both containers are open at the top, and both contain water) I watched an MIT video of professor Walter Lewin, who used these very same illustrations and stated that the pressure at point A and point B are the same. (see minutes 18 through 21 of the video: http://www.youtube.com/watch?v=265icrI3HkM&feature=related) Although it is not intuitive, I accept that the pressure is the same at the bottom of both containers. My question is this.... Imagine that the bottom of both containers is actually a piston (of equal area in both containers). Obviously there is a smaller amount of weight sitting on the piston in the left container, as opposed to the right container. So intuitively, to begin ejecting water out the top of each container, I have assumed that less upward force would need to be applied to the piston of the left container... than the piston of the right container (more total water weight over the same piston area). My confusion is how the pressure on the piston inside both containers can be the same.... yet the force needed to eject water out the top of both containers is different.