How we breathe: the bell-jar lung model
Pull and push the rubber diaphragm of a bell-jar lung model, watch the balloon lungs fill and empty, and see what a hole in the chest does.
Core concept
When the diaphragm moves down, the chest gets bigger, the pressure inside falls and air flows into the lungs
Topic: Human body
In the bell-jar model, the Y-shaped tube stands for the windpipe (trachea) and bronchi, the two balloons are the lungs, the jar is the chest and the rubber sheet is the diaphragm, a sheet of muscle under the lungs. When you breathe in, the diaphragm contracts and moves down (and the ribs move up and out). The chest gets bigger, so the pressure inside falls below the air pressure outside, and air flows in and fills the lungs. When you breathe out, the diaphragm relaxes and domes up, the chest gets smaller, the pressure rises and air is pushed out.
What you will learn
- Name the parts of the respiratory system that the model represents.
- Explain how the diaphragm makes air move into and out of the lungs.
- Calculate the air breathed in per minute.
Before you start
- Know that air moves from high pressure to low pressure.
Materials
- Two small balloons, a sheet of rubber (a cut balloon), string, tape
Equipment
- Bell jar or cut plastic bottle, Y-shaped tube, rubber bung
Procedure
- Pull the rubber sheet down by 2 cm or more and record what happens to the balloons.
- Push the sheet up and record what happens.
- Make a hole in the jar, pull the sheet down again and record.
- With the jar sealed and a 3 cm pull, record the air breathed per minute at 12 and 24 breaths per minute.
How this simulation is simplified
- Moving the rubber sheet 1 cm changes the space inside the jar by 100 mL.