A model of breathing has a bell jar. A rubber sheet closes its open bottom…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A model of breathing has a bell jar. A rubber sheet closes its open bottom. A Y-shaped tube goes through the cork at the top. Two small balloons hang inside the jar on the arms of the Y.
- Which part of the body does each of the following stand for: the bell jar, the rubber sheet, the balloons, the Y-shaped tube?
- The rubber sheet is pulled down. What happens to the volume and to the pressure inside the jar?
- What do the balloons do, and why?
- The sheet is let go. What happens now?
Need a reminder? The key ideaShow
In inspiration the diaphragm and the external intercostal muscles contract, the volume of the chest rises and the pressure in the lungs falls below atmospheric pressure. In expiration they relax and the pressure rises slightly above atmospheric pressure. Air moved in a minute rate volume of each breath.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) The bell jar is the thoracic chamber. The rubber sheet is the diaphragm. The balloons are the lungs. The Y-shaped tube is the trachea and the bronchi.
Step 2. (b) When the sheet is pulled down, the volume of the jar rises, and the air pressure inside the jar falls below the atmospheric pressure.
Step 3. (c) The air outside is at a higher pressure, so it flows in through the tube and the balloons fill, as lungs do in inspiration.
Step 4. (d) When the sheet is let go, the volume falls and the pressure rises. Air flows out and the balloons empty, as in expiration.
Answer: (a) chest, diaphragm, lungs, windpipe and bronchi; (b) volume up, pressure down; (c) they inflate; (d) they deflate.
Watch out. The balloons are passive. They do not pull the air in. The air is pushed in by the higher outside pressure.
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