You will need

• One glass bottle
• One coin (2 Pounds or 2 Euros work well)
• Freezer

What to do

1. Place the open bottle in the freezer for 10 minutes.
2. Remove the bottle from the freezer and moisten the rim of the mouth with some water.
3. Cover the rim of the coin with some water, so that nor air can pass through.
4. Place your hands around the bottle.
5. Observe what happens.

Background

You will be able to observe the coin moving as if a ghost was in the bottle. The cold air in the bottle is warmed by your hands and expands. The coin and water prevent the air from escaping the bottle. However, if the pressure gets high enough, the coin acts like a valve and moves releasing the warm air from the bottle.

You can watch the video for this experiment on YouTube: