Bubble (physics)

A bubble, in physics, is generally a thin film of liquid enclosing a volume of gas or vapor. The film is typically stabilized by surface tension, which minimizes the area of the film for a given enclosed volume. This minimization results in the characteristic spherical or near-spherical shape of isolated bubbles in a fluid medium.

The formation of bubbles is often driven by processes that introduce gas or vapor into a liquid. Examples include boiling, where vaporization creates bubbles of vapor within the liquid, and aeration, where gas is injected into the liquid. The stability of a bubble depends on factors such as the liquid's surface tension, the pressure difference between the inside and outside of the bubble (Laplace pressure), and the presence of surfactants that can reduce surface tension and prevent bubble coalescence.

The internal pressure within a bubble is higher than the external pressure due to the surface tension of the liquid film. This pressure difference is described by the Young-Laplace equation. The dynamics of a bubble's growth and collapse are complex, involving fluid dynamics, heat transfer, and mass transfer.

Bubbles play a significant role in various physical phenomena and technological applications. Cavitation, the formation and collapse of bubbles in a liquid subjected to rapid pressure changes, can cause erosion and noise in hydraulic systems. Bubble columns are used in chemical engineering for gas-liquid reactions. The study of bubbles is also crucial in understanding phenomena such as boiling heat transfer and the behavior of foams.