Soap Bubbles

A. Colors

1. What colors are in soap bubbles?

Have students observe soap bubbles (blowing one large bubble on a piece of black construction paper is a good way to observe a soap bubble). Children will probably observe all of the colors of the rainbow which is correct. They should also notice that the colors are always changing. This is because the light is reflected from both the inside and the outside of the film forming the bubble. When the light from the inside and outside interfere with each other colors are reinforced or canceled, thus causing the change in color. Color will also be affected by the thicknes of the bubble which is also changing as water evaporates. Glycerin slows the evaporation rate and thus increase the life of the bubble.

2. Can you change the colors in a soap bubble?

Prepare different colored soap bubble solutions (see recipes), by adding food coloring. Have the children observe a bubble from each and determine which has the most colors, prettiest, etc. Although the answers will vary, in fact they should all produce the same colors, because the thickness of the soap bubble is the same for each and the slight amount of absorption due to the food coloring should not appreciably affect the overall color.

3. What is the last color in a soap bubble?

If you observe a soap bubble until it breaks, the last color would be when the bubble is the thinnest and there is the least reflection, so the color is that of the background which would be black if you made your soap bubble on a piece of black construction paper.

B. Shapes

1. Does the shape of the wand change the shape of a soap bubble?

Have the students make wands from coated wire (available in spools at Radio Shack approx. #22 , a piece about 20 cm long works well) into different shapes. e.g. circle, square, triangle, heart, etc. (for Kindergarten you may want to make these shapes for them!). Ask the students to predict the shape of the soap bubble for each wand (drawing a picture for each is a good way to practice collecting data). After all predictions are made have the students blow bubbles with each wand and record the NEW shapes. They may be surprised to find that ALL bubbles are round (spheres)!! The reason being that a sphere is the most efficient way of enclosing a space, it uses the smallest amount of material and structurally very strong.


2. Are there any other shapes of soap bubbles?

Ask your students if they have ever seen a soap bubble that was another shape (other than a sphere) ? They should tell you that they have seen double, triple and multiple bubbles. Ask them to make a wand that can make these bubbles. They may try a figure eight wand, or a circle within a circle. Have fun. By the way there is a whole level of math involved with the shapes formed where the bubbles come together. maybe I will follow up on that one in the future!!

C. Sizes

1. How big can you make a soap bubble?

You can make a soap bubble wand from a coat hangar, or from a piece of rope attached to a wooden dowel, or you can purchase a commercially made wand. All will work well to make some rather large soap bubbles. Of course only your imagination will limit what you can use to make large soap bubbles, just remember that you will need a shallow basin the diameter of your wand (unless you use the sliding wand available in the stores) and that you want to avoid small bubbles in your solution.

2. What determines the size of a soap bubble?

The physical size is a function of the surface tension of the liquid (remember how some insects can walk on water, that is because water has a very strong surface tension). Well, the soap solution you are using has a surface tension that is caused by the combination of ingredients used in making it! Actually pure water has the greatest surface tension, but does not have the other properties necessary to make bubbles. Another factor that comes into play is density. As long is the bubble is less dense than air it will go up, if it is more dense than air it will go down, so you will not be able to appreciate your bubble as long!! And of course the size of the wand will affect the size of your bubbles, also.

D Solutions

1. You can purchase commercially prepared solutions.

2. Make your own solution.

A simple recipe that works well is : 1 part detergent (dish) to 1 part glycerine (available in a drug store as glycerine) to 6 parts water (preferably distilled).

You can vary the recipe, add food coloring, vary the detergent used, use corn syrup in place of the glycerine etc, to make some interesting experiments for your students. Which makes the most bubbles, the prettiest, the biggest, etc.

E. References

Activities in Science, The Center for Elementary Science, Fairleigh Dickinson University

Soap Bubbles, C.V.Boys