Hey, I was just thinking a bit about vacuum and air pressure and suddenly came over something really simple I cannot explain. I know that it is the external air pressure that makes two halves of a hollow sphere containing vacuum stick together like in this picture: http://www.radicalart.info/physics/vacuum/guericke/GuerickeHorses-S.jpg But, what if the two halves were made of solid metal? Like, if I put a book on my desk, so that there is no air between them, why wont the pressure from the atmosphere make it stick? Why is it necessary with a vacuum? As far as I know, there should not be any additional pressure other than the normal force due to gravity , coming from the table, pushing against the atmospheric pressure, so this is bothering me a bit :/ Thanks!