“Your Lungs Can’t Inflate Themselves!?” Learning How Breathing Works with a Plastic Bottle Model (Diaphragm & Lungs)

I’m Ken Kuwako, a Science Trainer. Every day is an experiment!

See How the Lungs Work with a Plastic Bottle and Balloons! A Simple Model for Science Class

“How do the lungs get air in and out?”

When tackling this question in the respiratory system unit for first-year junior high students, a hands-on model can make a huge difference in their understanding. Here’s a simple lung model that can be made using everyday materials. All you need is a 500 mL plastic bottle and a couple of balloons. Something that might otherwise be sitting forgotten in the corner of a science lab can be transformed into a tool that lets students experience the wonders of the human body firsthand.

What’s more, this particular model was designed and made by a student teacher using their own creativity and ingenuity. When students see it in action, they often respond with an impressed “Whoa!” Despite its simplicity, the model makes the mechanics of breathing surprisingly intuitive.

■ Materials (for one model)

• 500 mL plastic bottle (with the bottom cut off)
• Red balloon (cut in half; one half is attached to the mouth of the bottle to represent a lung)
• Blue balloon (attached to the bottom to represent the diaphragm)
• Cellophane tape or rubber band

■ How to Make It and How It Works

1. Cut off the bottom of the plastic bottle. (For safety, it’s best for the teacher to do this part in advance using a cutter or similar tool.)

2. Attach the red balloon to the mouth of the bottle, letting it hang down inside. This represents the “lung.”

3. Stretch the blue balloon over the cut-off bottom of the bottle. (Use the rounded part of the cut balloon and stretch it over the opening.) This represents the “diaphragm.”

4. Pull the blue balloon downward, and the air pressure inside the bottle decreases, causing the red balloon (the “lung”) to expand. Push the blue balloon upward, and the “lung” contracts.

This simple movement allows students to experience an important fact: the lungs don’t inflate by themselves. Instead, air moves in and out as the surrounding muscles, including the diaphragm, move.

Pull down on the diaphragm (blue), and the lung (red) expands.

Push up on the diaphragm (blue), and the lung (red) contracts.

■ Tips for Using the Model in Class

• Visually demonstrate that the lungs themselves do not contain muscles that make them expand and contract.

• Explain how changes in air pressure cause air to flow in and out.

• Have students work in groups. If the teacher prepares the bottle in advance, including the cutting, the activity will run much more smoothly.

If you have students make the models themselves, take extra care when handling the blue balloon used for the diaphragm. It is thin and tears easily, so having plenty of spare balloons on hand is a good idea.

This is a wonderfully simple teaching tool that can turn everyday materials into an instant “Ah, now I get it!” moment. If you have some spare time, make a few models in advance and keep them on hand. You’ll be glad to have them when the right opportunity comes along!

There is also a simulation available on the site below. Having students try the simulation themselves alongside the physical model should help deepen their understanding even further.

肺が動く瞬間を、指先で操作せよ！ 「見る、動かす、考える」理科シミュレーションサイトの衝撃

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