Friction friction and wear in so-called self-lubricating materials. Fluid friction occurs between fluid layers that are moving relative to each other. This internal resistance to flow is named "viscosity". In everyday terms, the viscosity of a fluid is described as its "thickness". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity. The less viscous the fluid, the greater its ease of deformation or movement. All real fluids (except superfluids) offer some resistance to shearing and therefore are viscous. For teaching and explanatory purposes it is helpful to use the concept of an inviscid fluid
Laminar flow the flow system and flow pattern. The common example is flow through a pipe, where the Reynolds number is defined as where: For such systems, laminar flow occurs when the Reynolds number is below a critical value of approximately 2,040, though the transition range is typically between 1,800 and 2,100. For fluid systems occurring on external surfaces, such as flow past objects suspended in the fluid, other definitions for Reynolds numbers can be used to predict the type of flow around the object. The particle Reynolds number Re would be used for particle suspended in flowing fluids, for example. As