If one pours these substances for example on an inclined plane, then honey flows clearly more slowly than water. Honey shows so to speak a high flow resistance, is thus less flowable. This characteristic of the flow resistance is called viscosity in the technical language. honey) Animation: Flow behavior of a low viscous fluid (e.g.įigure: Flow behavior of a low viscous fluid (e.g. Not only liquids show a viscous behavior, but also gases. With gases the viscosity is however less pronounced. Viscosity is a measure of the internal flow resistance of a fluid! Derivation of viscosity Such viscous substances such as liquids and gases are also generally referred to as fluids (lat. How can viscosity be described mathematically? First of all, it makes sense to think about what the actual cause of viscosity is. One can imagine the fluid for this purpose as being composed of many small layers. Due to the intermolecular forces of attraction of the molecules, these layers adhere to each other. These attractive forces act like frictional forces, which are one of the reasons for the viscous behavior of the fluid. The viscosity is therefore often referred to as internal friction. The viscosity is a measure of the strength of adhesion between the fluid layers! Figure: Influence of the surface area on the shear force The viscosity can therefore be formulated more precisely: For this reason, each layer prevents the adjacent fluid layer from flowing. Viscosity can thus be defined by the force required to move these imaginary fluid layers against each other. For this purpose, the fluid is thought to be enclosed between two horizontal plates. The lower plate is fixed and the upper plate is movable. When the upper plate is moved, the fluid layers must be sheared off against each other. This requires a more or less strong force depending on the viscosity.
The variables influencing this force are explained below. Animation: Definition of dynamic viscosity Influence of speed Such a flow between two surfaces moving relative to each other is also called Couette flow.
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