This simple Bell jar model lung can be used to demonstrate the basic principles of breathing. The model should be assembled as in the diagram. A swimming cap makes a suitable diaphragm. The cap can be attached to the bottom of the bell jar, and the balloons can be attached to the Y shaped tube, with elastic band s or plastic coated wire.

How the Model Works

The cavity inside the bell jar is airtight.

• As the diaphragm is pulled down, the volume of the cavity increases. This causes the pressure to fall. Air rushes in to equalise the pressure causing the balloons to inflate.
• As the diaphragm is pushed up, the volume of the cavity decreases, the pressure rises, and the air rushes out of the ballons causing them to deflate.

See Also

• Constructing school science lab equipment
• Respiration
• Respiratory system
• School Biology experiments and demonstrations
• How-to