Why were some bubble domes stronger than others?

When you tested different bubble recipes, some bubbles popped quickly while others stretched further and lasted longer.

The difference came from the bubble film.

A bubble is made from an incredibly thin layer of water held together with the help of soap.

Changing the ingredients changed how that thin film behaved.

That meant some recipes produced stronger, more flexible bubbles than others.

What is a bubble actually made from?

A bubble is not just air.

It is a very thin film of water and soap wrapped around air.

Soap molecules spread through the water and help the liquid form a flexible film.

Even though the bubble wall looks almost invisible, it can stretch surprisingly far without breaking.

What does surface tension have to do with it?

Water molecules attract one another.

At the surface, this attraction creates a force called surface tension.

Surface tension naturally pulls the surface of water together.

Soap changes this.

It reduces the surface tension enough for the water to spread into a thin film that can stretch around trapped air.

Why did changing the recipe matter?

Each recipe contained a different mixture of ingredients.

Changing the amount of detergent, glycerol or water changed the properties of the bubble film.

Some mixtures produced films that stretched further.

Others were weaker and popped more easily.

By changing one ingredient at a time and comparing the results, you were carrying out a fair test.

How does glycerol make bubbles stronger?

Bubble films contain water, and that water slowly evaporates into the air.

As the film loses water, it becomes thinner and more likely to break.

Glycerol can help the bubble film hold onto water for longer.

That can give the film more time to stretch before it becomes too thin and pops.

Why do bubbles form domes?

A bubble film is constantly being pulled by surface tension.

It naturally tries to form a shape with as little surface area as possible.

A free-floating bubble forms an almost perfect sphere.

When the bubble sits on a wet surface, the surface underneath cuts off part of the sphere.

That is why you created a bubble dome.

What did your experiment discover?

Your different bubble recipes gave you evidence.

You could compare:

• which bubble grew the largest

• which lasted the longest

• which stretched the furthest

• which popped most easily

The strongest bubble was not just the one that looked best.

It was the one supported by your observations and measurements.

By comparing the recipes, you were investigating how changing a material can change its properties.

Where is bubble science used?

Bubble science is useful far beyond bubble wands.

Scientists study bubbles and foams in cleaning products, firefighting foams, medical materials and manufacturing.

In each case, they need to understand how liquids, gases and surface-active chemicals interact.

Tiny changes to a mixture can make a foam stronger, longer-lasting or easier to break apart.

Curiosity Spark

You discovered which recipe produced the strongest bubble dome.

But what would happen if you changed:

• the amount of glycerol?

• the type of detergent?

• the temperature of the water?

• the size of the bubble wand?

Could you change one variable at a time and create an even stronger bubble recipe?

Try These Next

Water Bug Challenge – Investigate surface tension and discover how some creatures can stay on top of water.

Dragon Snot – Explore another strange material and discover how changing ingredients can completely change the way a material behaves.