Boyle's Law is very important in diving. In diving, the lungs are under intense pressure, and so that drastically changes volume. If you take a breath at the surface of a body of water, it is at a pressure of about 15 psi from the atmosphere. If you dive to a depth of about 33 feet or 10 meters (slightly less for salt water), the pressure will double to 30 psi. The volume of your lungs will be halved! And if you take a full breath of compressed air at 33 ft, heading back to the surface the volume of that air will double! That's why you have to exhale on the return trip, or else your lungs would explode.

Format The movie is in Macromedia Shockwave. There is also a movie in Apple QuickTime format. If you can't get either movie, here is the script.

Did you know that every few seconds you demonstrate Boyle's Law? The human body is a large pressure chamber for breathing. Your diaphragm is like a large elastic cover to your rib cage. Your lungs are just large elastic bags, like balloons. When you inhale, your diaphragm lowers, creating a low pressure area in your lungs (greater volume). Because air moves to the area of least pressure (Bernoulli Principle), air goes into your lungs. When you exhale, the opposite happens. Your diaphragm raises, decreasing the volume of your lungs and creating a high pressure area. The air is then forced out of your lungs by the increased pressure.

You can create a model lung to help demonstrate this principle. You need:

• straw
• styrofoam cup or similar container
• two balloons
• clear packaging tape

What you do:

1. Cut a hole the size of the straw in the bottom of the cup.
2. Cut a small window in the size of the cup (not large enough to make it easily crumpled!). Seal the window with clear packaging tape on either side of the opening (leave no air holes).
3. Affix a balloon to one end of the straw so the mouth of the balloon covers the opening in the straw.
4. Slide the other end of the straw through the hole in the bottom of the cup, so the balloon is inside of the cup. Fix the straw in place.
5. Cut the other balloon in half, tie the mouth closed, and stretch the balloon across the mouth of the cup.

You've made a model lung! To use it, pull down on the "diaphragm" and watch the balloon inside inflate. Here is a drawing you can model on. It is a cut away view (that's not how big the window should be!).

Another fun use of Boyle's Law is in making a barometer.

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