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Elastic Soap

In this demonstration, the students compare the elasticity of bubbles and balloons.

Bubbles seem to have a lot in common with balloons. They’re both made of a stretchy substance surrounding some air and they’re both elastic. In other words, when you stretch a balloon and a bubble and then let go, both will return to their original shape.

Blow up a balloon, then let go—the balloon goes back to its deflated form.

Start blowing a bubble, then stop—the bubble becomes a flat bubble film again. The big difference is that after a balloon is deflated it loses all its tension, but a bubble film always  has its stretch no matter how small it gets.

Other things that have elasticity are rubber bands, steel coat hangers and underwear. Even human skin is elastic—it’s the loss of elasticity that causes wrinkles! 

Objectives

  • Make a bubble and understand its structure.

  • Compare the elasticity of a bubble with the elasticity of other objects.

Materials

Key Questions

  • How does a bubble differ from a balloon?
  • When does a bubble pop?
  • What is elasticity?
  • What other things in our lives are elastic?

What To Do

  1. Blow up a balloon part way and hold it as you let the air escape. Observe the stretchy balloon shrink back to its original shape.
  2. Dip the wand into the bubble solution. Pull out a sheet of soap film and gently wave the wand up and down. Observe the soap film bulging out of the wand, forming a dome shape and then returning to a flat film when the wand is still.
  3. Compare the two and discuss the concept of elasticity.

You may also like to demonstrate that it is possible to skewer a balloon without it popping!

Extensions

  • How does elasticity help make bubbles?
  • What would happen if the bubble solution didn’t have elasticity?

Other Resources

Exploratorium | Bubbles
Soap Bubbles | Soapbubble.dk