How Are Bubbles Created?
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The Composition of Bubbles
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Bubbles start as a mixture of soap and water. When stretched into a thin film, the bubble fills with air or gas and assumes a spherical shape. Bubbles cannot maintain their shape when made with just water because the soap stabilizes the bubble's surface. The soap strengthens weak areas in the film and decreases the bubble's surface tension. This decrease in tension is what allows the bubble to hold its shape.
How Bubbles Form
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When a mixture of soap and water comes into contact with a hollow-centered surface such as a bubble wand or the opening of a detergent bottle, the solution stretches from one edge to the other to form a solid film. As air or gas is directed toward the taut surface of the film, the surface of the bubble begins to stretch away from the surface. As the bubble stretches, the soap molecules work to stabilize the weak points in the bubble's surface. Eventually, the bubble closes off or pops because the surface tension of the film has grown too high to support the bubble's delicate structure.
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Why a Sphere?
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Bubble are always sphere-shaped. This is not a fluke; the bubble's shape has everything to do with its surface composition. The soapy film has a very low surface tension before it's filled with air or gas because of the distribution of the soap. As the bubble grows larger, the soap becomes less concentrated in the film. This means that the surface tension rises. The bubble must form into a shape that compensates for that rise in surface tension. Spheres require the lowest possible surface area to enclose a given volume. This means that, of all the shapes a bubble could possibly form, the sphere puts the least amount of pressure on the surface layer.
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- Photo Credit Marinka van Holten
