# Bubble Mix Recipe

The best bubble mix recipe ever! Make your own bounty of beautiful bubbles.

## Australian Curriculum links

• Mathematics > Measurement and Geometry > Year 1 > ACMMG022
• Science > Chemical Sciences > Year 5 > ACSSU077
• Science > Physical Sciences > Year 5 > ACSSU080

## You'll need

• 7 parts water
• 3 parts detergent (Morning Fresh Original works well)
• 1 part glycerine (from supermarkets or pharmacies)
• A suitable sized container with a tight-fitting lid for storage
• Wire coat-hangers or plastic-coated wire (eg. garden ties)

## Try this

1. Pour all of the ingredients into your storage container.
2. Stir the mixture slowly and thoroughly.
3. Let the bubble mix sit for as long as you can before using it. The longer you leave it, the better it will work.
4. Bend the wire coat hangers into a variety of shapes such as circles, stars, triangles and squares. These are the ‘bubble wands’.
5. Dip your bubble wand into the bubble mix, remove it and let any excess bubble mix drip into the container, then move the wand slowly through the air to make beautiful bubbles!

Handy hint: Your bubbles will last longer in moist air. If you are trying to make bubbles on a dry day or in an air-conditioned room, try spraying water in the air to make your bubbles last longer.

## What's happening?

The beauty of bubbles is all to do with their physical properties: they reflect all the colours of the rainbow, they are spherical and they are light enough to float in the air.

When you make a bubble, you stretch bubble mix around a volume of air. The bubble mix forms a thin film which is stretchy and flexible (elastic). The thin film traps the air inside the bubble and forms a sphere. The reason bubbles are spherical in shape is to do with the elasticity of the thin film and the pressure of the air trapped inside the bubble. If we assume that we can’t change the volume of air trapped inside a bubble, the thin film has to stretch into a shape that can contain the volume of air. The sphere is the shape with the smallest surface area for a given volume. It takes energy to stretch a thin film and having the smallest possible surface area means that the thin film does the smallest amount of stretching which means it requires the smallest amount of energy. The air inside the bubble is pushing out against the thin film in all directions and the thin film is pushing in on the air because the thin film is elastic, making the bubble lovely and smooth and almost as light as air.

The reason bubbles are so colourful is because of the way the light is reflected from the thin film. If we assume you are looking at a bubble under white light such as sunlight or a white electric light, some of the white light bounces (reflects) off the top of the thin film and some bounces off the bottom of the thin film. The reflected white light from the top and the white light from the bottom interfere with each other (thin film interference). White light is made up of all the colours of the rainbow and when white light interferes with white light, some of the colours can disappear (destructive interference) whereas other colours can become brighter (constructive interference). Which colours disappear and which ones get brighter depends on the thickness of the thin film and the angle of the light. We see lots of colours in bubbles because they are constantly moving, changing the angle from which we see the reflected light, and the thickness of the thin film changes as the bubbles mix falls to the bottom of the bubble due to gravity and the bubble dries out.

## Real world links

Fluids can do freaky things in space! During a six month stay on the International Space Station, NASA astronaut Don Pettit conducted a series of experiments on fluid dynamics that became known as the ‘Symphony of Spheres’. He made a sphere of water which resembled a crystal ball and then used a thin tube to inject air into the sphere, creating a small bubble of air. As he injected more air into the sphere, the bubble of air became bigger and moved in strange and beautiful ways within the water sphere. Droplets of water were then injected in to the bubble of air. The water droplets moved around inside the bubble, bouncing off each other and off the inside of the bubble. See a video of these amazing bubbles on YouTube.