A bottle lung model is a simple school project that shows how your lungs fill with air and empty again. The plastic bottle acts like the chest cavity, the balloons act like the lungs, the straw acts like the windpipe, and the stretched balloon at the bottom acts like the diaphragm. This model matters because it turns an invisible body process into something you can see and control.
By pulling and pushing the bottom balloon, students can observe how breathing depends on changes in air pressure and volume.
Key Facts
- When the diaphragm moves down, chest volume increases and air pressure inside decreases.
- Air moves from higher pressure to lower pressure.
- Inhaling in the model happens when the bottom balloon is pulled downward.
- Exhaling in the model happens when the bottom balloon is pushed upward.
- Volume up means pressure down, and volume down means pressure up.
- A simple pressure relationship is P1V1 = P2V2 when temperature stays constant.
Vocabulary
- Diaphragm
- The diaphragm is a dome-shaped muscle below the lungs that helps pull air into the body when it contracts.
- Lungs
- The lungs are organs that take oxygen from inhaled air and help remove carbon dioxide from the body.
- Trachea
- The trachea is the windpipe that carries air between the mouth or nose and the lungs.
- Air pressure
- Air pressure is the push caused by air particles hitting the surfaces around them.
- Chest cavity
- The chest cavity is the space inside the rib cage that holds the lungs and heart.
Common Mistakes to Avoid
- Leaving gaps around the straw is wrong because air leaks prevent the balloons from inflating properly. Seal the opening with clay, tape, or putty so air can only move through the straw.
- Using balloons that are too stiff is wrong because they may not expand when the pressure changes. Stretch the balloons first or use thinner balloons that inflate easily.
- Pulling the bottom balloon sideways is wrong because the model works best when the diaphragm balloon moves straight down and up. Pull gently downward to increase the bottle's inside volume.
- Thinking the diaphragm pushes air directly into the lungs is wrong because the diaphragm changes volume and pressure. Air flows in because outside air pressure becomes higher than pressure inside the chest cavity.
Practice Questions
- 1 A student pulls the diaphragm balloon down 4 cm and observes that each lung balloon inflates to about 60 mL. What is the total air volume in the two lung balloons?
- 2 A class builds 5 lung models. Each model uses 1 plastic bottle, 3 balloons, 2 straws, and 1 rubber band. How many balloons and straws are needed for all 5 models?
- 3 In the lung model, explain why the two balloons inside the bottle get larger when the bottom balloon is pulled downward.