What caused the can to collapse?
Before we started the can was filled with water and air. When we heated the can it caused the liquid to turn to gas (Vapor) when the water boil. The vapor from the boiling water pushed air out of the can. Now the can is filled with water vapor, we cooled it suddenly by inverting it in water. Cooling the can caused the water vapor in the can to condense, creating a partial vacuum. The extremely low pressure of the partial vacuum inside the can made it possible for the pressure of the air outside the can to crush it.
A can is crushed when the pressure outside is greater than the pressure inside, and the pressure difference is greater than the can is able to withstand.
Measure how much more water is now in the can that the air pressure pushed in.
Adult Supervision is required!
CAUTION: Do not heat the can over high heat when it is empty. This may cause the ink on the can to burn or the aluminum to melt.