Expansion of gasses We need a bottle and a coin. Put the bottle in a fridge to cool. Rub soap and pour water on the neck of the bottle a little bit. Put the coin on the neck of the bottle to cover it. Put your hands on the bottle, hold it fast and think hard about making the coin jump. In a while, it works! Your hands warm the bottle, the bottle warms the air inside, and warm air wants to escape. When the pressure of the air is great enough, the coin jumps.