Boil small amount of water in can.
Hot water vapor fills can.

                       Invert can in cool water. Close up of crushed can.
		       Water vapor condenses.
		       Pressure drops and atmospheric pressure crushes can.
click here for a more detailed explanation of coke can crushing demo.

Air pressure holds board on bottom of glass.

Red lead ball rests on top of beans.      After shaking red ball "sinks" and ping pong bell rises from bottom.

Diet coke can floats while Classic Coke can sinks (due to the dense sugar in it) in water.

		   Adding salt to water makes it denser
		   and the Classic Coke can floats. 

Marshmallows expand in a vacuum jar as the air in their pores expands.  After the pores burst and air is let back into the jar the marshmallows collapse.