Show Me Some Science! Can Crush

A metal can and a hose are filled with water, and the hose is lowered off of a second floor balcony. The water drains and the can is crushed!

In a fluid, like water or air, the pressure is always greater on the bottom than on the top. This is because the weight of all of the fluid pushes down on the fluid below it. Water is a fluid, and the bottom of the hose has the same pressure as the atmosphere since it is open to the air. As gravity pulls the water out of the hose and the can, the pressure inside of the hose and can decreases. Eventually the pressure on the inside is so low that the pressure on the outside of the can is enough to crush it!