What it shows
Bubbles are always round, whatever the shape of the wand. Soap film pulls itself into the shape with the least surface, which is a sphere.
The science
A soap bubble is a thin film of soapy water holding air. The film pulls on itself in every direction and tries to have as little surface as possible. A sphere has the smallest surface for a given volume. So every free bubble becomes round, even if blown from a square or a star wand.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Four pipe cleaners or thin wires (under Rs 50)
- A cup of water with 3 spoons of dish soap
- A tray
- A spoon of sugar
- A straw
Safety
For this project: Keep soap away from eyes. An adult must watch and wipe the floor when it gets slippery.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Mix three spoons of soap with a cup of water and stir without making foam.
Add a spoon of sugar to make bubbles last longer.
Bend pipe cleaners into a circle, a square, a triangle and a star with a handle.
Dip the circle wand in the mixture and blow gently.
Dip the square wand and blow, and see the shape of the bubbles that float away.
Try the triangle and the star.
Draw what you see for each wand.
Blow a bubble with a straw on a wet tray and look at the half-bubble.
What you should see
Bubbles from every wand are round, even when the wand is square or star-shaped.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What shape is every bubble?
A sphere, which looks round.
2Why is it always round?
The soap skin pulls to make the smallest surface.
3What is inside a bubble?
Air.
4What colours can you see on a bubble?
Rainbow colours, from light on the thin film.
Take it further
Make giant bubbles with a loop of string on two sticks.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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