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Square Bubbles

In this activity, students use 3-D bubble wands to observe the minimal structures of soap film and blow non-spherical bubbles.

Because soap film is elastic, it arranges itself to form surfaces with the smallest possible area within its constraints.

Free-floating soap bubbles are always spheres because a sphere encloses the given volume of air with the minimum soap film surface.

Can bubbles form shapes other than a sphere?

Yes, they can, but only when they’re supported by other soap films. You can make these supporting films by dipping 3-D frames into the soap solution.

The soap films that remain attached to the frames shows the minimum surface structure, but when you blow a bubble where the soap films meet, you create a 3-D bubble in the shape of the frame!

Some students may notice that the soap film cubes and tetrahedrons are not mathematically perfect—the walls bulge out slightly. This is because there is excess air pressure inside the walls of the bubbles.

Objectives

  • Use their knowledge of soap films and minimal surface structures to make bubbles of various sizes, shapes, and arrangements.

Materials

  • Per Group:

    1 tub of All Purpose Bubble Solution

  • Per Student:
    1 3-D bubble wand
    1 straw
    various materials to make 3-D bubble wands (optional)

Key Questions

  • Why does a 3-D frame make a difference to the shape of a bubble?
  • Does the frame create a bubble of the same shape when you dip it into the solution?
  • What does it create?
  • What happens when you try to release your cube bubble into the air?
  • What role does surface tension play?

What To Do

Preparation

  1. Create 3-D bubble wands in the shape of cubes and tetrahedrons using pipe cleaners or similar materials.
  2. Prepare enough All Purpose Bubble Solution for each group (or each student) to have one small tub.

Activity

  1. Look at your 3-D bubble wand and predict the structure that the soap film will create.
  2. Dip the 3-D bubble wand into the bubble solution to coat it with soap film. Observe the minimum surface created by the soap film inside the shape. Was it what you expected?
  3. Dip one end of the straw into the bubble solution to make it wet.
  4. Insert the wet end of the straw into the centre where all the bubble films meet.
  5. Blow gently into the other end to create a bubble. What shape is it?

Extensions

  • Build and test other 3-D bubble wand shapes.
  • You can make 3-D frames using materials such as pipe cleaners, straws and string, wooden skewers and polystyrene joints, wire coat hangers, large paper clips, K’NEX toys, toothpicks and modelling clay.