Surface Tension – Soap Bubbles

Surface Tension – Soap Bubbles

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The surface layer of liquids has a thin elastic “skin” called surface tension. You can see surface tension at work when you see a drop of water – it creates a little “bead” of water, like a little dome. Surface tension is what makes the dome shape – the water doesn’t flatten out.

Water is made up of two kinds of atoms, hydrogen and oxygen. The name for the water molecule is H20. The water molecule has 2 hydrogen atoms and 1 oxygen atom. Water molecules are attracted to each other because hydrogen atoms and oxygen atoms are attracted to each other and hug close together really tight. This is called cohesion. The molecules hug so close together they don’t want to touch other molecules around them. That’s why a bubble is round and only rests a small part of itself on a surface when it lands.

When you blow air into soap bubble solution the liquid molecules want to attract to each other again so they wrap around the burst of air until they can attach to each other again – this is what makes the round bubble shape. The air inside the solution is pushing the molecules in the soap bubble solution apart but the attraction between the soap bubble solution molecules is so great, the bubble doesn’t pop – the molecules are hugging each other too tight.

To experiment with bubbles you need a good bubble recipe. Below are some simple recipes to try. Each of the recipes use water and dish soap. The “other” ingredient can be baking powder, corn syrup, glycerin (sold at the pharmacy) or sugar. We had the best luck with baking powder. The baking powder recipe made some HUGE bubbles.

Science Project Idea:

Mix different formulas of bubble mix and test them to see which one makes the best bubbles. Use the same amount of water and the same amount of dish soap in at least three different buckets. Choose one “Other” ingredient and add it in different amounts to each of your trial buckets. To be fair, you should hold the bubble wand in front of a fan instead of trying to blow on it, that way you know that the amount of air being blown to make the bubble will be exactly the same. Test the three formulas several times and record your results on a chart. Decide before you begin what property you are looking for in the bubbles. Are you going to test which formula makes the biggest bubble, the bubble the last the longest without popping or the formula that makes the most bubbles?

Here are some books and websites that will help you understand and have fun with bubbles:

  • Exploratoriuam: Bubbles
  • Bubblesphere
  • Homemade Bubble Solutions
  • The Ultimate Bubble Book There are 3 fun activities in this book – Person Inside a Bubble (Page 41) Giant Bubbles (Page 48-51) Printing With Bubbles (Page 52-53)
  • Google Preview: Science Experiments That Explode and Implode: Stink Bombs (bubbles that stink! pages 22-23)
  • Prize Winning Science Projects for Curious Kids: The Bubble Olympids (pages 102-103)

More IndyPL Experiments about Surface Tension:

Ultimate Bubble Book How to Make Bubbles Science Experiments That Explode and Implode Prize Winning Science Projects

Words to Know:

Surface Tension – The film that forms on the surface of liquids caused by the attraction of the particles in the surface.
Cohesion – The attraction between like molecules; to stick together.

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