Grits and Purls

Spinning yarns about the grit of life

IMG_0205Spring has sprung and with it so have the bubble wands. My daughter even put a jar of bubble juice and some bubble wands in her bike basket and toured around the neighborhood sharing her love of bubbles with her friends. Bubbles are indeed magical, and since the earliest age she has enjoyed chasing bubbles around the yard, catching them in the bathtub, and making giant bubbles using a homemade wand and homebrew bubble juice. And I have enjoyed having an excuse to play with bubbles myself.

At the Discovery Center in Rockford, our favorite exhibits are the giant bubble and the bubble window.

When you stop and think about it, bubbles are fascinating. Why do they form perfect spheres and not cubes or some other shape? How do they form the fascinating multicolored films that you see? Why can you only “catch” bubbles when your hands are wet and soapy?

It turns out there is a lot of science in those shimmering orbs that we chase around our yards on summer evenings.

A bubble is a very thin layer of film (made of water and soap molecules) surrounding a volume of air. That thin layer of film is stretchy and has surface tension. A soap bubble never loses its tension, and it forms the shape that requires the least amount of surface area to trap the air within the film. That shape happens to be a perfect sphere. (Now, you can get a bubble to form as a square, if you start out with a cube-shaped bubble wand, but that is not the usual state of affairs.)

Since bubbles minimize surface area to contain the air within them, when bubbles meet they combine to share walls, and those walls always meet at 120° angles. If you were to take two clear sheets of glass, coat them in soapy water and hold them about one-half inch apart and blow bubbles between them, you would see that the bubble walls that form look much like the cells of a bee honey comb. They form hexagons. This hexagon structure is the very best structure for minimizing the surface area needed to contain the maximum volume. Both bees and bubbles are being highly efficient when they use this structure.

The myriad of colors we see in bubbles results from the way that light is reflected from the surface of the bubble, and the colors that are reflected change with the thickness of the bubble. Thicker bubbles may reflect green, blue or magenta light. As the film thins, the color darkens, and the thinnest part of the bubble will get quite dark right before it pops. Can you watch the colors in a bubble change and predict when it is going to pop? It’s fun to try.

I love marveling at things like bubbles, but I love even more understanding those things. Bubbles are no less fun because I understand some of the physics and chemistry that make them so beautiful. They are actually more fun to play with, because now I know enough to ask questions about them—to say “What would happen if I did this or that?”

So as the spring time warms and summer approaches, get your bubble wands ready for a little chemistry and physics, and enjoy a little of the majesty of bubble-logy.

© 2014 Michele Arduengo. All rights reserved.

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