Ghost In A Bottle

We used to do this science project as kids. All you need is a quarter and a glass bottle (we used to use the Clearly Canadian drink bottles but I don't know if that drink is around anymore. Any glass bottle will do as long as the opening is small enough that a quarter won't fall in). Place the empty glass bottle in the freezer for an hour or so. Take the bottle out of the freezer and place the quarter over the bottle opening. The cold air starts to warm up, causing the air in the bottle to expand. As the air expands, it tries to escape. This causes the quarter to rattle around, just like if there was a ghost in the bottle trying to escape. Easy science project for kids.