You will need:
1. Cut the bottom off the plastic bottle and cut the top off one of the balloons.
2. Stretch the balloon tightly over the bottom of the container so it forms a thin skin like the surface of a drum, and secure very firmly with stickytape.
This balloon represents the diaphragm.
3. Make a hole through the bottle lid and attach a straw. Place the other balloon inside the lid, with the top of the balloon attached to the straw with the rubber band - the balloon should sit inside the bottle. This balloon represents the 'lung'.
4. Carefully pull the balloon at the base of the bottle and watch the 'lung' balloon inflate.
How to teach science, the way primary kids love