Liquid bubble

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Bubbles of air in a soft drink

For specific types of bubbles, and metaphors of the word "bubble", see Bubble (disambiguation).

A bubble is a globule of one substance in another, usually air in a liquid.

Due to surface tension, bubbles may remain intact when they reach the surface of the immersive substance.

1 Common examples
2 Physics and chemistry of bubbles
3 The appearance of bubbles
4 Applications
5 Vibration
6 References
7 See also

[edit] Common examples

A bubble of gas in a tar pit

Bubbles are seen in many places in everyday life, for example:

As spontaneous nucleation of supersaturated carbon dioxide in soft drinks
As water vapor in boiling water
As air mixed into agitated water, such as below a waterfall
As sea foam
As given off in chemical reactions, e.g. baking soda + vinegar
As a gas trapped in glass during its manufacture

[edit] Physics and chemistry of bubbles

Bubbles form, and coalesce into globular shapes, because those shapes reduce energy. For the physics and chemistry behind it, see nucleation.

[edit] The appearance of bubbles

Humans can see bubbles because they have a different refractive index than the surrounding substance. For example, the IR of air is approximately 1.0003 and the IR of water is approximately 1.333. Snell's Law describes how electromagnetic waves change direction at the interface between two mediums with different IR; thus bubbles can be identified from the accompanying refraction and internal reflection even though both the immersed and immersing mediums are transparent.

One should note that the above explanation only holds for bubbles of one medium submerged in another medium (e.g. bubbles of air in a soft drink); the volume of a membrane bubble (e.g. soap bubble) will not distort light very much, and one can only see a membrane bubble due to thin-film diffraction and reflection.