Crushing Pop Cans:

Preparing for the project-
1.) Empty Pop Cans
2.) A Pair of Tongs
3.) Hot Water
4.) Cold Water

 
What to do-
After the water is heated (you can use a Bunsen burner to heat the water) place the can with the open side up using the tongs-do not completely submerge the can.  After a few minutes place the can upside down in the cold water - you should see the can collapse.  Another method for heating the can is to place it directly above the flame for a few seconds, using the tongs.

What is going on?
When the can is heated from below the gas inside the can expands.  Then, by placing the can upside down in the cold water you create a vacuum inside the can, now forcing the gas to condense.  The atmospheric pressure from outside of the can causes the pressure on the outside of the can to be greater then the pressure on the inside of the can thereby collapsing the cans walls.

Equations-
Pressure=Force / Area