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Human Lung Simulator

Students make a model of the human lung with a pop bottle, straw, and balloons. "Winds will blow from high to low" applies even during breathing!

When we breathe in, the volume of the chest cavity is increased. Since there is more space available, the air pressure in the chest cavity and lungs is reduced, creating a low-pressure system in your body. The air outside your body immediately rushes in to equalize the lower pressure, flowing through the nose or mouth into the lungs. When we breathe out, the chest cavity contracts, increasing the air pressure in the lungs. The high-pressure air in the lungs rushes out of the nose and mouth to equalize the low-pressure zone of air around the body.

When the students pull the balloon diaphragm downwards they increase the volume of the model lung and therefore decrease the pressure inside. This causes the surrounding air to rush into the lung (going from high to low pressure), making the balloon lung inflate. The air in the balloon is trying to "fill in" the low-pressure zone inside the bottle. This mimics inhalation.

When the balloon diaphragm is pushed upwards, the volume of the bottle decreases, increasing the air pressure in the bottle. This causes the air in the bottle to push against the balloon, forcing the air out of it (high pressure air in the bottle wants to fill the low-pressure area outside). This mimics exhalation.

Objectives

  • Explain how air pressure works.
    Discuss how air pressure affects our daily lives.

Materials

  • Sharp knife/box cutter
    Pair of scissors

    Per student:

    Plastic pop bottle (2L or 500mL)
    2 balloons
    Plastic straw
    Clay or plasticine
    Tape or 2 elastic bands
    Pair of scissors
    Pencil

Key Questions

  • What happened when you pulled down on the diaphragm? What happened when you let go of the diaphragm? How does this compare to how your lungs and diaphragm work together? How do we breathe? How is breathing connected to air pressure? Do all animals breathe this way?

What To Do

Note: For younger students cut the plastic bottles beforehand.

  1. Explore and discuss: How does your body breathe? What happens as you inhale? What happens when you exhale? Before or after experiment ask students to place their hands on their side ribs while they take a few deep breaths.
  2. Distribute materials to each student/group.
  3. Cut bottle two-thirds from the top, the initial cut can be made with a box cutter or similar, complete the cut using scissors. Dispose of the bottom third.
  4. Secure the intact balloon to the end of the straw with an elastic band or tape, so that the seal is airtight. This is the “lung.”
  5. Poke a hole through the clay with a pencil.
  6. Insert the non-balloon end of the straw through the hole in the clay, taking care not to plug the straw with any clay (you will need a clear passage for the air to travel through the straw). There should be about 8 centimetres of straw between the clay and the balloon.
  7. Place the straw through the mouth of the plastic bottle so that the straw is sticking out of the bottle and the balloon is hanging inside. Use the clay to secure the straw to the bottle and seal the edges. Allow at least 2 centimetres of space between the bottom of the balloon and the bottom of the bottle.
  8. Cut the neck off of the second balloon.
  9. Stretch the cut balloon across the open bottom of the bottle. Secure this balloon with an elastic band and/or tape. This is the “diaphragm.”
  10. Pull or press on the stretched balloon ‘diaphragm’, causing the balloon inside to inflate or deflate to simulate inhaling and exhaling.

Extensions

  • How could you modify this model to include two lungs? Can you get your model to mimic sneezing or coughing? Find out what causes hiccups.

Other Resources

Science World Resources | Full lesson & other activities |  Air