Collapsing can or can crusher experiment is a demonstration of an aluminum can being crushed by atmospheric pressure. Due to the low pressure inside a can as compared to the pressure outside, the pressure outside exerts a force on the can causing the can to collapse.
Explanation
The demonstration starts with boiling water inside the can. As the water is boiled, water vapor is created and fills the space inside the can which then pushes the air out.
H2O → H2O
Then, inverting a water vapor-filled can into a water bath causes the water vapor to rapidly condense back to liquid water. The condensation of water reduces pressure inside the can, so the higher pressure outside the can makes the can collapse.
H2O → H2O
Limitation
There will be an impeding event that could occur which is water in the water bath being drawn inside the can by the reduced pressure. As a result, in a basic demonstration, only an aluminum can is able to be used since it is not very strong. Unlike other stronger can such as steel can, the aluminum can will be collapsed before the water can be drawn inside the can. Nevertheless, Professor Julius Sumner Miller could make a steel drum collapse by sealing the opening of the drum after the water inside the drum boils and pouring water and ice onto the drum surface.
Alternatives
Addition of sodium hydroxide to a can filled with carbon dioxide can produce a similar result.