Bubble Thing

Introduction

One of the most common items found in toy stores is soap bubbles. They are usually accompanied by small plastic wands, or occasionally, a bubble pipe or more complicated type of apparatus. The Bubble Thing consists of a plastic rod with a fabric loop attached which can produce huge bubbles several feet in length. The Bubble Thing was invented by a Harvard architecture graduate, David Stein, for his daughter.

Concepts

  • Interference
  • Surface tension

Materials

Soap bubble solution
Bubble Thing
Bucket

Safety Precautions

Bubbles break with a fair amount of force; keep away from your face. Solutions will make the floor or pavement slippery; use caution to avoid falling. The Bubble Thing should be used outdoors. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information. Wash hands thoroughly with soap and water before leaving the laboratory.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Soap solution may be stored in an air-tight plastic bottle or rinsed down the drain with an excess of water according to Flinn Suggested Disposal Method #26b.

Prelab Preparation

  1. A simple solution for making soap bubbles can easily be prepared in the home or laboratory. To make one liter of soap bubble solution, mix 100 mL of Dawn® or Joy® dishwashing liquid with 50 mL of glycerin to bucket.
  2. Add this to 850 mL of distilled water.
  3. Stir the soap, glycerin and water mixture. Do not shake—such action produces excessive suds.

Procedure

  1. While keeping the loop closed, dip the fabric loop into a bucket of soap bubble solution.
  2. Lift the loop out of the bucket and let the excess soap bubble solution drip off.
  3. Open the loop carefully.
  4. Wave the Bubble Thing slowly.
  5. Close the loop and enjoy!

Teacher Tips

  • The bubble solutions commonly available in toy stores are dilute soap or detergent solutions that are good for making small bubbles, but not particularly effective for large bubbles.
  • For producing large, long-lasting soap bubbles, increase the amount of the detergent to 200 mL, the glycerin to 100 mL, and then add to 700 mL of distilled water. Again, stir the solution. You may have to experiment with your soap mixture to get very large bubbles.
  • Use only distilled or deionized water when preparing a soap bubble solution to prevent interference from dissolved metal ions present in tap water. If the solution does not seem to work well, let it sit for a few days to a week. Aging seems to improve the characteristics of soap solutions.

Correlation to Next Generation Science Standards (NGSS)†

Science & Engineering Practices

Constructing explanations and designing solutions
Developing and using models

Disciplinary Core Ideas

MS-PS4.A: Wave Properties
MS-PS4.B: Electromagnetic Radiation
HS-PS4.A: Wave Properties
HS-PS4.B: Electromagnetic Radiation

Crosscutting Concepts

Cause and effect
Structure and function

Performance Expectations

MS-PS4-2: Develop and use a model to describe that waves are reflected, absorbed, or transmitted through various materials.

Discussion

A soap bubble is round since the surface of the soap film which forms the bubble will try to contract to take up the smallest surface area. In nature, the volume with the smallest surface area is a sphere.

One reason that a bubble breaks is that it hits something dry. The other reason is a result of the water in the walls of the bubble draining to the bottom of the bubble. This produces a small bump on the bottom of a large bubble from which one can observe the water dripping. When the top of the bubble becomes too thin to support the total mass of the bubble, it breaks. The addition of glycerin, or other viscous material, adds strength to a bubble since this material does not drain out of the soap film readily.

The colors observed on a soap bubble are a result of thin film interference and the changing thickness of the film due to the draining liquid. Although a bubble is transparent, like glass, some light is reflected off the outside surface of the soap film. Some light is also reflected off the inside surface of the film. When the two reflected light waves meet, they may be in-phase (the waves aligned peak to peak and trough to trough) or out-of-phase (non-aligned). In-phase light waves produce the same color as the incoming light (e.g., white light) making the color appear brighter. This is called constructive interference. Out-of-phase light waves produce interference effects which we see as color. If the light waves are out-of-phase so that the peak of one wave is aligned with the trough of the reflected wave, then the light cancels itself and no color is seen. This is called destructive interference. As the thickness of the soap film changes, the distance the light travels changes, and the different interference effects give different colors. When just about all the water is drained out of the upper part of the soap bubble, the wall becomes so thin that the light reflected from the top surface cancels itself (when light is reflected, all peaks become troughs) and dark spots appear in the soap film. The swirling effects are a result of the uneven thickness in the soap film as the water drains.

References

Special thanks to David A. Katz, retired, Wilmington, DE, who provided Flinn Scientific with the instructions for this activity.

†Next Generation Science Standards and NGSS are registered trademarks of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.