 As a demonstration of atmospheric pressure, we place some water inside a large metal can. We've heated the water up to the boiling point and the steam has displaced all the air in the can. We'll now tightly cap the can. The steam inside the can will condense. This will produce a very low pressure inside the can. There's atmospheric pressure on the outside of the can. We'll add some cold water on top of the can. The can collapses due to the large difference in pressure.