Chattering Coin

It must be cold!.

 

 

 

Category - Heat & Temperature

Key Idea - Thermal Expansion

 

Purpose - The Chattering Coin shows how air expands when it is heated.

The coin, ready to chatter.
Nature -  Demonstration
Materials -  A boiling flask (or 2 litre soft drink bottle), a coin large enough to cover the mouth of the flask, access to a freezer
Method - 
  1. Place the boiling flask in the freezer for a couple of hours.
  2. Take the flask out and place the moistened coin over the mouth of the bottle.
  3. Place your hands on the outside of the flask and watch the coin chatter up and down.
Safety - Nil 
Explanation - The air inside the freezer is cold and therefore also very dense.  The coin seals the mouth of the flask so that as your hands warm the air inside and it expands the coin flutters up and down to allow it to escape.
Notes - The same principle is shown with the  Auto-inflating Balloon Wizard.