Thursday, June 26, 2014

Air Pressure: Exploring How Lungs Work

Lungs make a great demonstration of how air pressure is used in our body.   We love to explore anatomy and physiology and this experiment is a great way to introduce a basic concept.  

This activity also builds really nicely on the Water Bottle Fountain activity that we have previously posted.   

We started by discussing how we get air into our bodies.  We put our hands on our chests and felt it expand (or go out) as we breathed in and contract (or go in) as we breathed out.  We then spoke about how we use our lungs to get the air we need.

But how does it get into our lungs?  We spoke about how the air goes in through our nose, down our air passages and into our lungs.   Then we got ready to build our lungs.

We used a straw for the air passages and inserted it into a balloon (our lung).  We secured the balloon with a rubber band to the straw.

We then took a water bottle to represent the chest cavity. One important note: make sure your bottle is strong - we used a water bottle the first time but it was weak and deformed easily.  When we repeated the experiment we used a tonic water bottle, and it was much stronger.  We still had to reinforce the bottom with tape to help prevent it from deforming.   The great thing about the water bottle was that the ridges felt like our ribs, but it was difficult to do the experiment.

With both bottles, we cut off the bottom of the bottle leaving a large enough volume for the balloon to hang inside.  Then we threaded the straw through the mouth of the bottle with the lung inside and sealed the top using molding clay.

As you can see. little Bear lost interest for a while and engaged in a game of peek-a-boo with the neighbors' dog.  Bug stayed pretty focused.

To make our diaphragm at the bottom we used a second balloon.  We tied the balloon closed and cut off the top third of the balloon.  The open portion of the balloon went over the cut part of the bottle and was secured in place with tape.  So now we had our model of a lung - air passages into the lung which sits in the chest cavity and the diaphragm muscle below.

We pulled to test it out and pulled our airways right out of the chest - whoops!  So make sure you hold the chest when making it breathe.

After a quick fix we were working again.

Now to make our lungs work (we took additional pictures without the kids to make sure we can show you the movement of the lung - thanks hubby!):

Breathing in: when the diaphragm muscle contracts it pulls down - so we pulled down on our diaphragm by pulling the tied portion of the balloon down.  

This expansion increases the volume which decreases the air pressure compared to outside.  Air flows in through the air passages from high pressure (outside) to low pressure (inside the lungs) and inflates the lungs.  We saw our lung balloon get bigger!

Breathing out:  when the diaphragm muscle relaxes it goes up - so we released our balloon.   

This decreased the volume of the chest cavity which increased the pressure in the cavity and on the balloon.  The air flows out through the air passages from high pressure (inside the lungs) to low pressure (outside) and deflates the lungs.  We saw our lung balloon get smaller!  

We saw it get even smaller when we pushed up on our diaphragm!

You can repeat these steps to mimic how we breathe in cycles.


  • straw
  • tape
  • strong clear plastic bottle - tonic water bottle worked well
  • rubber band
  • clay/silly putty
  1. Insert a straw into the mouth of the balloon and secure with an elastic band.
  2. Cut off the bottom of a plastic bottle and wrap a few pieces of tape around the bottom of the bottle to reinforce it.
  3. Thread the straw through the mouth of the bottle so that the balloon is inside the bottle.  Seal the mouth of the bottle with clay and wrap in tape to make it extra secure.
  4. Tie a balloon closed and cut off the top 1/3.  Take the open part of the balloon and cover the open bottom of the bottle.  Secure the balloon to the bottle with tape.
  5. Suck most of the air out of the lung-balloon.
  6. Pull down on the knot in the balloon on the bottom of the chest and see what happens to the lung.
  7. Release and see how the lung changes.


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