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Daisies in STEM - Soap Bubbles

Every kid likes soap bubbles, especially giant soap bubbles. I've been toying with the idea of making giant soap bubbles all summer. Today we experimented with different soap solutions and learned about surface tension.

The surface layer of liquids has a thin elastic "skin" called surface tension. In water droplets, the surface tension is what gives the droplet its dome shape. When air is blown into a soapy mixture, the liquid molecules try to stay together, wrapping around the air to form a bubble. The composition of the soapy mixture will affect the surface tension and thus the size and stability of the bubble.

For our first experiment, we tried forming bubbles by blowing air into the following solutions: water, water+soap, water+soap+glycerine, water+soap+food coloring, and water+soap+sugar. As expected, water bubbles did not last very long. Soapy water with either glycerin or sugar lasted the longest. However, most of the girls really liked making colored bubbles.

Next, we tested the shape of soap bubbles. Will a square wand make square bubbles or a triangular wand make triangular bubbles? I prepared 3-dimensional bubble wands using pipe cleaners and straws, and the girls prepared their own wands from pipe cleaners. We tried the different wands and discovered that bubbles are always round regardless of the shape of the wand. The reason for that, is the surface tension of the soap bubble.

I wanted to show the girls that a square bubble can be formed in the middle of the square wand, but it was too wind outside and the bubble just flew out of the wand in a perfect round shape...

Finally, the girls took turns in making huge bubbles using a solution for giant bubbles I found here:

The solution contains 6 cups of water, 1/2 cup of Dawn dish soap, 1/2 cup of corn starch, 1 tablespoon glycerin, 1 tablespoon of baking powder.

Needless to say the giant bubble were a hit :)


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