As educators, we are continually designing new methods and procedures to enhance learning. During this process, good ideas are frequently generated and tested, but the extent of such activities may not be adequate for a full manuscript. Nonetheless, the ideas may be quite beneficial in improving the teaching and learning of physiology. Illuminations is a column designed to facilitate the sharing of these ideas (illuminations). The format of submissions is quite simple: a succinct description of about one or two double-spaced pages (less title and authorship) of something you have used for the classroom, teaching, lab, conference room, etc. You may include one or two simple figures or references. Submit ideas for inclusion in Illuminations directly to the Associate Editor in charge, Stephen DiCarlo ([email protected]).

Because respiration deals with gases, a thorough understanding of the physical principles relating to the behavior of gases is important for understanding respiratory physiology. However, the concepts and physiological significance of the gas laws and properties of gases are often difficult for students to grasp. To help students understand these concepts, simple experiments are often utilized, because “[a]pretty experiment is in itself often more valuable than twenty formulae extracted from our minds…” [Albert Einstein]. Students examine the force of ambient pressure, observe the concept of pressure gradients, experience the force of compressed air with three simple, inexpensive classroom experiments that are conducted during the lecture: “The Collapsing Can,” “The Balloon Inside the Bottle,” and “The Compressed Air” experiments. For the Collapsing Can experiment, we place 15 ml of water into an empty soft-drink can and boil the water on a hot plate for approximately 1 min. As the water boils, a cloud of condensed vapor escapes from the opening in the can. At this point, and using tongs, we grasp the can, invert it, and dip it into a beaker of water. The can collapses immediately with an impressive crush! The explanation for the collapsing can is that the vapor from the boiling water forced the air out of the can. Cooling the can by dipping it into a beaker of water condensed the water vapor, leaving the can empty. When the can was empty, the ambient pressure (pressure outside the can) crushed it (pressure outside greater than pressure inside).

For the Balloon Inside the Bottle experiment, we place 15 ml of water into an empty Pyrex bottle and boil the water on a hot plate until the water is almost gone. At this point, we remove the bottle from the heat and stretch the opening of a balloon over the opening of the bottle. As the bottle cools, the balloon is pushed into the bottle and inflates to fill the entire inside of the bottle. Again, the vapor from the boiling water forced the air out of the bottle. The balloon blocked the entrance to the bottle, and as the bottle cooled the water condensed, leaving the bottle empty. When the bottle was empty, the ambient pressure (pressure outside the bottle) rushed in (pressure outside greater than pressure inside), inflating the balloon.

Finally, for the Compressed Air experiment, we place a balloon into an empty bottle and stretch the opening of the balloon over the opening of the bottle. Students try to inflate the balloon in the bottle. No student has ever been able to inflate the balloon in the bottle, because the bottle is full of air. When the students blow into the balloon, the air in the bottle is compressed. The compressed air exerts more pressure on the balloon than even the largest student can blow into it.

Students’ eyes light up when these concepts are illustrated by simple experiments.