# Liquid bubble

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Liquid bubble

A bubble is a globule of one substance in another, usually gas in a liquid. Due to surface tension, bubbles may remain intact when they reach the surface of the immersive substance.

Common examples

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

Physics and chemistry

Bubbles form, and coalesce into globular shapes, because those shapes are at a lower energy state. For the physics and chemistry behind it, see nucleation.

Appearance

Humans can see bubbles because they have a different refractive index (IR) 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.

Applications

Nucleation can be intentionally induced, for example to create bubblegram art.tHThe bubble is sometimes a triangle a square or a rectangle. They can't be poped because they are really made out of concrete

Pulsation

When bubbles are disturbed, they pulsate (that is, they oscillate in size) at their natural frequency. Large bubbles (negligible surface tension and thermal conductivity) undergo adiabatic pulsations, which means that no heat is transferred either from the liquid to the gas or vice versa. The natural frequency of such bubbles is determined by the equation: [Minnaert, Marcel, On musical air-bubbles and the sounds of running water, Phil. Mag. 16, 235-248 (1933).] Leighton, Timothy G., The Acoustic Bubble (Academic, London, 1994).]

:$f_0 = \left\{1 over 2 pi R_0\right\}sqrt\left\{3 gamma p_0 over ho\right\}$

where:
* $gamma$ is the specific heat ratio of the gas
* $R_0$ is the steady state radius
* $p_0$ is the steady state pressure
* $ho$ is the mass density of the surrounding liquid

Smaller bubbles undergo isothermal pulsations. The corresponding equation for small bubbles of surface tension σ (and negligible liquid viscosity) is

:$f_0 = \left\{1 over 2 pi R_0\right\}sqrt$3 p_0 over ho}+{4 sigma over ho R_0

Excited bubbles trapped underwater are the major source of liquid sounds, such as when a rain droplet impacts a surface of water. [cite journal
last = Prosperetti
first = Andrea
coauthors = Oguz, Hasan N.
year = 1993
title = The impact of drops on liquid surfaces and the underwater noise of rain
journal = Annual Review of Fluid Mechanics
volume = 25
pages = 577–602
doi = 10.1146/annurev.fl.25.010193.003045
url = http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.fl.25.010193.003045
format = PDF
accessdate = 2006-12-09
] [cite web |url=http://ffden-2.phys.uaf.edu/311_fall2004.web.dir/Ryan_Rankin/bubble%20resonance.htm |title=Bubble Resonance |accessdate=2006-12-09 |last=Rankin |first=Ryan C. |year=2005 |month=June |work=The Physics of Bubbles, Antibubbles, and all That]

* Sonoluminescence
* Bubble fusion
* Underwater acoustics

References

* [http://www.physicstoday.org/pt/vol-56/iss-2/p36.html Bubble physics] – touches on vapor pressure, bubble formation, bubble dynamics, cavitation, acoustic oscillations, sound of raindrops underwater, Rayleigh-Plesset equation, snapping shrimp, lithotripsy, ultrasonic cleaning, sonochemistry, sonoluminescence, medical reperfusion imaging, and micro-bubble therapy
* [http://natgeochannel.co.uk/podcasts/?id_p=272250478 Extra large bubbles]

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