Take a Deep Breath for this Impromptu Physics Lesson

Last night, as the kids were playing with their current favorite App, Human Body by TINYBOP, Molly asked about the diaphragm.  As I had completely forgotten we each had one of those, Joe jumped in to explain the physics of how we breath with our diaphragm.  For those that didn’t pay attention in, what was it, Biology?, here’s a quick explanation:

When you inhale, your diaphragm, which is a muscle, tightens and moves down. This creates more space in your chest cavity, into which your lungs expand.  As your lungs expand, air is sucked in through your nose and/or mouth.  The muscles between your ribs (called intercostal muscles) also go to work here.  Your intercostal muscles tighten, but instead of moving down, they pull your rib cage up and out.  In doing so, they help enlarge the chest cavity.

When you exhale, your diaphragm relaxes and moves back up into the chest cavity. The intercostals also relax and reduce the space in your chest cavity.  As the space in the chest cavity gets smaller, air rich in carbon dioxide is forced out of your lungs then out of your nose or mouth.

If you want to learn more, click here.

So how do you explain this to kids and Mommy?

You don't need anything fancy to teach science at home.

You don’t need anything fancy to teach science at home.

Stuff you Need

  • 1 jar
  • 2 plastic bags
  • 1 straw
  • 2 rubberbands

Take a plastic bag, wrap it tightly around the end of a straw and fasten it with a rubber band (so that it looks like a balloon).  If you have a balloon, you can use that instead.

Put the straw, bag side down, into the jar.

Cover the jar with another plastic bag, making sure to poke the straw through it with as small a hole as possible.  You need to make sure no air can get in or out through that hole.  Fasten the second bag around the neck of the jar, making it fairly taut over the jar’s opening, using the second rubber band.

Pull up and down on the baggy covering the jar (this represents the diaphragm).

Look through  the jar and you will see the bag on the end of the straw (here, representing the lung) filling and emptying as you pull on the baggy.

You can see a cool 3-D animation of this process here.


It’s only a minute and as Molly says, “it’s so cool.”  So, check it out.

Also, if you have any interest in teaching your kids (or yourself) about their bodies, check out Human Body.

It is easy to navigate, very informative, and the kids love to learn how to care for the human body.  It has lead to lots of great questions.

It covers everything from eating, to digestion ( Joseph and JohnJohn, and OK, all of us, are still howling about the toots that really come out of the large intestine), to the various systems (muscular, skeletal, etc.).  At $2.99, it’s a fair deal.

They even include a handy Human Body Guidebook, which you can find here.  You can use it with or without the App.


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