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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.

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

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

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

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.

Nucleation can be intentionally induced, for example to create bubblegram art.

When bubbles are disturbed, they oscillate in size at their resonant frequency, determined by the equation:

where:

• γ is the specific heat ratio of the gas
• R₀ is the steady state radius
• p₀ is the steady state pressure
• ρ is the density of the liquid

Excited bubbles trapped underwater are the major source of liquid sounds, such as when a rain droplet impacts a surface of water. ^[1][2]

1. ^ Prosperetti, Andrea; Oguz, Hasan N. (1993). "The impact of drops on liquid surfaces and the underwater noise of rain" (PDF). Annual Review of Fluid Mechanics 25: 577-602. DOI:10.1146/annurev.fl.25.010193.003045. Retrieved on 2006-12-09. 
2. ^ Rankin, Ryan C. (June 2005). Bubble Resonance. The Physics of Bubbles, Antibubbles, and all That. Retrieved on December 9, 2006.

• Sonoluminescence
  • Bubble fusion