Coin launcher Experiment

When you cool air it shrinks, extra air is pushed into the bottle.

Then the wet coin seals the top of the bottle as it freezes. So as the temperature increases the pressure builds up.

This means that when you heat up the air again with your hands, it pushes outwards harder and harder until the pressure on the bottom of the coin is large enough to break the ice around it. As the ice breaks the coin is pushed upwards and flies away from the bottle.