>>13751679LOL I like this answer.
OP, buddy, if you pull a suction cup from a wall, why is it so hard?? It's because air molecules apply 1 atm of pressure on the cup: to pull the cup from the wall is to pull against 1 atm of pressure on the surface of the cup. What force is on the opposite side to oppose the cup? There's little to no air, so their's little to none.
So how does a suction cup stick to a wall? The atmosphere pushes it stuck (plus friction).
Same thing applies if it's a mercury liquid sticking to a 1-end open pipe
