Bubble Shapes
Kathleen Damonte
Few can resist a bubble wand and a brightly colored bottle of bubble solution. Although playing with bubbles might seem like just a fun outdoor activity, it is also an opportunity to explore some interesting science concepts related to soap, light, and color.
What do you think is inside a soap bubble? If you guessed air, you are correct. Soap bubbles are air surrounded by a thin film of water and soap. The soap film wraps around the air and traps it within. The soap film is elastic—that means it is stretchy. Bubbles that are floating freely in the air are usually spherical (round). A sphere is the smallest surface area that can contain the air inside with the least amount of stretching for the soap film. A bubble that is blown on top of a wet surface uses that surface as a wall and will contract to form a dome shape.
Bubble Colors
The colors you see in a soap bubble come from white light. White light is actually composed of seven colors: red, orange, yellow, green, blue, indigo, and violet. When white light passes through a transparent material, such as the soap film that makes up the bubble wall, the different colors separate so they can be seen. A bubble wall is extremely thin, just a few millionths of an inch thick. When a light wave hits the outside of the bubble wall some of the light is reflected back to your eye. Light waves are also reflected back from the inside of the bubble wall. These reflected waves interact in a complicated process that produces the colors you see. As the bubble wall gets thinner and thinner, the bubble loses color. A bubble will look black at the top just before it pops.
Why Do Bubbles Pop?
Bubbles pop for several reasons. Bubbles pop when the water in their bubble wall evaporates. When bubbles are blown outside in the sun they evaporate more quickly. They also pop because of contact with wind, a dry surface, or dry air. To have the best results when working outdoors with bubbles, work in an open, shady area and keep all materials wet with bubble solution.
Try experimenting with bubble domes by following the directions below.
Resources
Bubbles: www.exploratorium.edu/ronh/bubbles/bubbles.html
Bubble Fun: www.reachoutmichigan.org/funexperiments/quick/bubblefun.html
The Art and Science of Bubbles: www.cleaning101.com/sdakids/bubbles/Welcome.html
Kathleen Damonte is a middle school science teacher in the Montgomery County Public School System in Maryland.
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Exploring Bubbles
For these activities you can use prepared bubble solution from the store or mix up some of your own bubble solution from the recipe below.
Materials:
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Cookie sheet with sides
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Bubble solution
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Plastic straw
* You will probably want to do these activities outside; it will make cleanup a lot easier. Pick a shady area with little wind.
Bubble Solution Recipe:
Mix the two ingredients together in an appropriate size container.
Directions:
1. Fill the bottom of the cookie sheet with bubble solution so the entire bottom is wet.
2. Dip the bottom end of the straw in the bubble solution.
3. Touch the straw at a 45-degree angle to the bottom of the cookie sheet and blow gently to create a dome.
4. Be patient—it may take a few tries to learn how to blow a bubble dome.
5. When making your bubble dome, be careful not to get any bubble solution in your mouth.
Activities and Questions:
1. Blow a bubble dome and touch it with a dry finger. Blow another bubble dome and touch it with a wet finger. What happens?
2. Blow the largest bubble dome you can. How were you successful in doing this?
3. Blow a bubble dome inside a bubble dome. How were you successful in doing this?
4. Blow two connecting domes, three connecting domes, etc. What happens where the bubbles join each other?
5. Blow a bubble dome and watch it carefully. What colors do you observe and how do they change? Try to predict when the bubble will pop. |
 Click here for PDF file.
Copyright © 2003 NSTA
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May 2003, p. 54-55