Give Now

A Moment of Science

Quick, Hide in Here!

Unfortunately, lying down in shallow water and breathing through a hollow reed won't work if you need a quick getaway. Learn more on this Moment of Science.

Shallow pond during day

Photo: Chad Horwedel (flickr)

Hiding in a pond like this one using a hollow reed won't work

Maybe you remember those old westerns where some outlaw is being chased by a posse, and in order to escape, he lies down in shallow water and breathes through a hollow reed. The posse, befuddled, rides on by.

Unfortunately, this trick doesn’t actually work. A little physics keeps getting in the way.

Taking a breath is such a common occurrence that we rarely even notice we are doing it, but every time we inhale, we are redistributing the air in our immediate vicinity. Our chests are expanding, both filling up our insides as well as pushing aside the air that surrounds us.

That’s easy enough to do with air, but water is a much denser medium. Pushing it aside takes some doing, as you quickly find when trying to wave your hand underwater. Also, unlike breathing above water, our cowboy is not just redistributing the medium. He is actually displacing the medium, water, in order to pull a pocket of air down into it.

As our cowboy begins to inhale, he will discover that the external pressure on his lungs exerted by the surrounding water is much greater than his muscular ability to inflate them. In essence, with every breath he has to push aside most of the water in the pond.

A swimmer with a snorkel can still breathe, but notice that snorkelers float right on the top. Were they to try sinking underneath, even a moderate amount, the same thing would happen.

The other problem is that a hollow reed is about as thin as a straw. Try breathing through a straw even above water and you’ll soon be gasping.

Stay Connected

What is RSS? RSS makes it possible to subscribe to a website's updates instead of visiting it by delivering new posts to your RSS reader automatically. Choose to receive some or all of the updates from A Moment of Science:

Support for Indiana Public Media Comes From

About A Moment of Science

Search A Moment of Science