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Blow soap bubbles to investigate the strength of surface tension

Suitable For

Grade 6



Time Required

 <12 Hours



What’s it about?

The surface of a liquid is held together by a strong force known as ‘surface tension’ and this same force is what causes water drops to form almost perfect spheres. Surface tension makes the surface of a liquid seems as if it has a thin, elastic skin over it. Study how ‘stretchy’ the skin on the surface of water can be by blowing bubbles in the following science experiment:

Topics covered

Surface tension, Soap bubble, Sphere, Cohesion

What will I need?


Procedure (Method)

Unfortunately, this section is only available in the e-book version of the project.

How does it work?

Unfortunately, this section is only available in the e-book version of the project.

Soap bubbles are ideally made up of a combination of soap and water because it allows the bubble to best maintain its shape, whilst filling the bubble with air. The soap’s role is to strengthen the weak areas in the water molecules and decreases the bubble’s surface tension allowing the bubble to hold its spherical shape as it fills with air. In this science experiment, a thin film is formed when the bubble blower or ‘wand’ is dipped into the soap / water solution.

When blowing on this film, it begins to stretch away from the direction of air stream. As the film forms a bubble, the soap molecules are drawn toward the weak points in the bubble, stabilizing those areas by decreasing the surface tension. The formed soap bubble must form into a shape that has the lowest possible surface area to put the least amount of strain on the soap molecules. Spheres have the lowest possible surface area to enclose a given volume hence the shape of the bubbles.

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