Yesterday, I made an experiment. I filled an empty (but contains air) soda can with a little bit of water. Then I turn on fire at the sides of the soda can so that the water starts boiling. Next, I prepare bucket filled with normal temperature water. And when the water inside the soda can starts evaporating, I quickly turn the SC upside down inside the bucket and then, CRANK! The air pressure made it's effect on the soda can.
However, I don't know why.
I explained it by saying: "The water vapour eliminates the air in the soda can, when we reverse it into the bucket, the water vapour quickly becomes liquid and we have a vacuum now in the soda so the effect of air pressure will be important."
But is it true?
Best Answer
Boiling water in the can produces steam which forces the air out of the can. Placing the can into the much cooler (compared to the boiling water) water causes the steam to condense back into liquid form. Flipping the can upside down prevents any air from rushing into the can. This results in the pressure inside the can (which is empty except for the liquid water) being much less than the air outside, crushing the can.
Sources: http://uw.physics.wisc.edu/~wonders/CollapseCan.html http://scienceline.ucsb.edu/getkey.php?key=1447