Viskositeettilaki

Viskositeettilaki, or the law of viscosity, is a fundamental principle in fluid mechanics that describes the relationship between the shear stress applied to a fluid and the resulting rate of shear strain. This law is most commonly associated with Newtonian fluids. For such fluids, the shear stress is directly proportional to the rate of shear strain. The constant of proportionality in this relationship is known as the dynamic viscosity of the fluid, often represented by the Greek letter eta (η). Therefore, the mathematical expression for this law is τ = η * (du/dy), where τ is the shear stress, η is the dynamic viscosity, and du/dy represents the velocity gradient perpendicular to the direction of flow.

The concept of viscosity itself quantifies a fluid's resistance to flow. A highly viscous fluid, like honey, flows slowly and offers significant resistance to deformation. Conversely, a low-viscosity fluid, such as water, flows easily. Viskositeettilaki explains that the internal friction within a fluid, which causes this resistance, is directly related to how quickly the fluid layers are sliding past each other. This law is crucial for understanding and predicting fluid behavior in various applications, including pipe flow, lubrication, and the design of aerodynamic and hydrodynamic systems. Non-Newtonian fluids, however, do not strictly adhere to this linear relationship, exhibiting viscosity that changes with the applied shear stress or shear rate.