Understand how the diaphragm works!
12 ounce sturdy plastic soda bottle
9" balloon (will be the "diaphragm")
12" balloon (will be the "lung")
Cut off the bottom of the soda bottle. Cut off the neck of the 9" balloon. It can help hold the balloon on the bottle if you leave the body-neck transition.
Stretch the 9" balloon (without neck) over the bottom of the bottle.
Dangle 12" balloon into the neck of the bottle. Keep it completely deflated.
Wrap the neck of the balloon around the mouth of the bottle. To create a vacuum for this to work correctly, let the air out of the top of the bottle while pressing in to the "diaphragm" at the bottom of the bottle.
Test your lung model!