A can filled with water, be heated so that water boils. Now seal the mouth with airtight cap. Let the can cool. It's sides get deformed. Why?
Higher air pressure on the outside of the can is the main reason for getting deformed. You can understand it as follows,
When water boils inside the can, a steam is produced. Or we can say that the boiling water inside the can produces water molecules in the gas state which are invisible. These molecules occupy all of the space in the can since the air molecules have been pushed out. The hot gas molecules in the can are at the same pressure as the air on the outside of the can.
Now, when the can is cooled, the hot gas water molecule are very rapidly cooled. Some of these gas molecules are condensed back to the liquid water, so there are less gas molecules present. The remaining gas molecules are also cooled by the cold water. Due to this the molecules slow down, then there are fewer collisions with the walls of the can, which in turn causes less pressure inside of the can. The air pressure on the outside of the can is stronger. This causes the can to be deformed.
When water boils inside the can, a steam is produced. Or we can say that the boiling water inside the can produces water molecules in the gas state which are invisible. These molecules occupy all of the space in the can since the air molecules have been pushed out. The hot gas molecules in the can are at the same pressure as the air on the outside of the can.
Now, when the can is cooled, the hot gas water molecule are very rapidly cooled. Some of these gas molecules are condensed back to the liquid water, so there are less gas molecules present. The remaining gas molecules are also cooled by the cold water. Due to this the molecules slow down, then there are fewer collisions with the walls of the can, which in turn causes less pressure inside of the can. The air pressure on the outside of the can is stronger. This causes the can to be deformed.