Rheology is the branch of physics concerned with the flow and change of shape of matter, primarily in a liquid state. Isaac Newton formulated a mathematical equation to predict the flow of a fluid, Newton's law of viscosity. Fluids which obey the law are referred to as Newtonian for example water and air. Non-Newtonian fluids do not obey the law: asphalt, blood, magma, shampoo, toothpaste and custard powder mixed with water or milk.

Physicists need to understand the dynamics of fluid flow in order to relate the knowledge to practical applications. Many manufacturing industries rely on their expertise, for example; food and drinks, glass and plastics, motor, oil/mineral extraction and oil refining. This also applies to fluid flow in the natural world and to biological processes in humans and animals.

When a bubble or vertical soap film is formed the liquid soap immediately begins to drain under the force of gravity, it becomes thinner at the top and thicker towards the bottom. Draining channels also form to facilitate flow, minute changes in atmospheric pressure will override gravitational pull and compromises the uniformity and direction of flow - hence, the swirling patterns.

Film thickness varies throughout the draining process, ranging from tens of nanometres, (a nanometre is a billionth of a metre) to several microns thick, (a micrometre is a millionth of a metre). Colourful, light interference patterns show clearly the direction and flow of the draining film. Whilst an understanding of flow dynamics in fluids without the capacity to produce light interference patterns is tricky, information gained from studying soap films is pertinent to understanding how mechanics of fluid flow.

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